City of Pekin Wastewater Facility Plan

Transcription

City of Pekin
Wastewater Facility Plan
Prepared for:
City of Pekin
400 Margaret Street
Pekin, IL 61554
Prepared by:
Harding ESE, Inc.
Peoria, IL
January 2001
Harding ESE Project No. 5399211
City of Pekin-Wastewater Facility Plan
Table of Contents
List of Tables ..............................................................................................................................................................iii
List of Figures.............................................................................................................................................................. v
List of Appendices...................................................................................................................................................... vi
1.0
SUMMARY, CONCLUSIONS AND RECOMMENDATIONS...........................................................1
2.0
INTRODUCTION ....................................................................................................................................3
2.1
2.2
STUDY PURPOSE AND SCOPE ...................................................................................................................3
PLANNING AREA .....................................................................................................................................5
3.0
COMMUNITY PROFILE .......................................................................................................................6
4.0
WASTEWATER EFFLUENT LIMITATIONS ..................................................................................10
4.1
4.2
5.0
CURRENT WASTEWATER SYSTEM...............................................................................................13
5.1
5.2
6.0
NPDES PERMIT ....................................................................................................................................10
FUTURE AND PENDING REGULATIONS ...................................................................................................12
WASTEWATER COLLECTION ..................................................................................................................13
WASTEWATER TREATMENT ..................................................................................................................13
WASTEWATER SYSTEM EVALUATION .......................................................................................15
6.1
INTERCEPTOR SEWERS ..........................................................................................................................15
6.1.1
Southeast Interceptor....................................................................................................................15
6.1.2
North Side Interceptor – STP #2 to STP #1..................................................................................15
6.1.3
South Side Interceptor ...................................................................................................................16
6.1.4
Northeast Interceptor ...................................................................................................................17
6.1.5
Impact of Lick Creek Interceptor..................................................................................................17
6.2
COMBINED SEWER OVERFLOW (CSO) STRUCTURES.............................................................................17
6.2.1
Fayette Street Outfall....................................................................................................................17
6.2.2
Court Street Outfall ......................................................................................................................18
6.2.3
Caroline Street Outfall .................................................................................................................18
6.2.4
State Street Outfall........................................................................................................................19
6.3
STATE STREET FIRST FLUSH BASIN .......................................................................................................19
6.4
FEDERAL CORRECTIONS INSTITUTE (FCI) .............................................................................................19
6.5
SEWAGE TREATMENT PLANT NO. 1 (STP#1)........................................................................................20
6.5.1
Pretreatment Facility....................................................................................................................20
6.5.1.1
6.5.1.2
6.5.2
6.5.2.1
6.5.2.2
6.5.3
6.5.3.1
6.5.3.2
6.5.4
6.5.4.1
6.5.4.2
6.5.5
6.5.6
6.5.6.1
6.5.6.2
6.5.7
6.5.7.1
6.5.7.2
6.5.8
General Description ................................................................................................................................. 20
Condition Evaluation ............................................................................................................................... 21
Primary Treatment .......................................................................................................................22
Primarily Effluent Pumping..........................................................................................................26
Secondary Treatment....................................................................................................................26
Effluent Disinfection .....................................................................................................................30
Sludge Handling/Processing ........................................................................................................30
Anaerobic Digestion .....................................................................................................................34
Metering/Instrumentation/Controls ..............................................................................................37
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6.5.8.1
6.5.8.2
6.6
SEWAGE TREATMENT PLANT NO. 2 (STP#2)........................................................................................42
6.7
CSO SETTLING AND CHLORINE CONTACT BASIN – STP #1..................................................................44
6.7.1
General Description .....................................................................................................................44
6.7.2
Condition Evaluation....................................................................................................................44
7.0
WASTEWATER SYSTEM IMPROVEMENT OPTIONS ................................................................45
7.1
COMBINED SEWER OVERFLOW STRUCTURES ........................................................................................45
7.1.1
Fayette Street Outfall....................................................................................................................45
7.1.2
Court Street Outfall ......................................................................................................................45
7.1.3
Caroline Street Outfall .................................................................................................................46
7.1.4
State Street Outfall........................................................................................................................46
7.2
7.3
FCI BAR SCREEN ..................................................................................................................................49
7.4
CSO SETTLING AND CHLORINATION BASIN – STP #1 ..........................................................................49
7.5
WASTEWATER TREATMENT-STP #1 .....................................................................................................52
7.5.1
STP #1 Replacement-General.......................................................................................................52
7.5.1.1
7.5.1.2
7.5.1.3
7.5.1.4
7.5.2
7.5.3
7.5.4
7.5.5
7.5.6
7.5.7
8.0
Primary Clarifiers..................................................................................................................................... 53
Secondary Clarifiers................................................................................................................................. 54
Disinfection System ................................................................................................................................. 55
Sludge Thickening and Dewatering ......................................................................................................... 56
STP #1 Upgrade-Conventional Activated Sludge Process ...........................................................58
Counter Current Aeration without Primary Treatment ................................................................63
Counter Current Aeration with Primary Treatment .....................................................................70
Sequence Batch Reactor (SBR).....................................................................................................74
Vertical Loop Reactor with Primary Treatment ...........................................................................79
STP#1 and STP#2 Upgrades ........................................................................................................84
IMPROVEMENT OPTION SELECTION ..........................................................................................85
8.1
COMBINED SEWER OVERFLOW STRUCTURES ........................................................................................85
8.2
8.3
FCI BAR SCREEN ..................................................................................................................................86
8.4
WASTEWATER TREATMENT ..................................................................................................................86
8.4.1
CSO Settling and Chlorination Basin – STP #1 ...........................................................................86
8.4.2
Treatment Systems ........................................................................................................................87
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Table of Contents (continued)
List of Tables
Table 1.1
Table 3.1
Table 3.2
Table 4.1
Table 4.2
Table 5.1
Table 6.1
Table 6.5.1
Table 6.5.2
Table 6.5.3
Table 6.5.4
Table 6.5.5
Table 6.5.6
Table 7.1.1
Table 7.1.2
Table 7.1.3
Table 7.2.1
Table 7.3.1
Table 7.4.1
Table 7.4.2
Table 7.5
Table 7.5.1
Table 7.5.2
Table 7.5.3
Table 7.5.4
Table 7.5.5
Table 7.5.6
Table 7.5.7
Table 7.5.8
Table 7.5.9
Table 7.5.10
Table 7.5.11
Table 7.5.12
Table 8.1
Table 8.2
Table 8.3
Summary of Wastewater Improvement Costs
City of Pekin, IL – Population Projection
Wastewater Projections
NPDES Regulated Outfalls
STP #1 Outfall – Effluent Limits
Historical Treatment Plant Loadings – Daily Average Values
Pre-treatment System – Condition Summary
Primary Treatment System – Condition Summary
Secondary Treatment System – Condition Summary
Sludge Handling/Processing – Condition Summary
Anaerobic Digestion – Condition Summary
Meters and Programmable Logic Controllers
Fayette Street Outfall – Cost of Improvements
Court Street Outfall – Cost of Improvements
Caroline Street Outfall – Cost of Improvements
State Street Basin – Cost of Flushing Improvements
FCI Bar Screen – Cost of Improvements
Option 1 – Wastewater Plant Basin – Cost of Flushing
Improvements
Option 2 – Wastewater Plant Basin – Cost of Flushing
Improvements
Wastewater System Options Evaluation- Disinfection
System
Construction Unit Costs
STP #1 – Existing – Wastewater Treatment Capacity
STP #1 Upgrade – Conventional Activated Sludge
STP #1 Upgrade – Conventional Activated Sludge – Annual
Operation and Maintenance Cost
STP #1 Upgrade – Counter Current System without Primary
Clarifiers
STP #1 Upgrade – Counter Current without Primary
Clarifiers- Annual Operation and Maintenance Cost
STP #1 Upgrade – Counter Current System with Primary
Clarifiers
STP #1 Upgrade – Counter Current with Primary ClarifiersAnnual Operation and Maintenance Cost
STP #1 Upgrade – SBR System
STP #1 Upgrade – SBR System – Annual Operation and
Maintenance Cost
STP #1 Upgrade – VLR System
STP #1 Upgrade – VLR System – Annual Operation and
Maintenance Cost
Combined Sewer Overflow Structures –Cost of Proposed
Improvements
State Street Basin – Cost of Flushing Improvements
FCI Bar Screen – Cost of Improvements
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List of Tables
Table 8.4
Table 8.5
Table 8.6
Option 2-Wastewater Plant Basin-Cost of Flushing
Improvements
Summary of Costs Analysis – Treatment
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List of Figures
Figure 3.1
Figure 3.2
Figure 3.3
Figure 3.4
Figure 4.1
Figure 6.1
Figure 6.2
Figure 6.3
Figure 6.4
Figure 6.5
Figure 6.6
Figure 6.7
Figure 6.8
Figure 6.9
Figure 6.10
Figure 6.11
Figure 6.12
Figure 6.13
Figure 6.14
Figure 6.15
Figure 6.16
Figure 6.17
Figure 6.18
Figure 7.2.1
Figure 7.4.1
Figure 7.5.1
Figure 7.5.2
Figure 7.5.3
Figure 7.5.4
Figure 7.5.5
Figure 7.5.6
Figure 7.5.7
Figure 7.5.8
Figure 7.5.9
Figure 7.5.10
Population Projection
Hydraulic Loading
Organic Loading Projection
Solids Loading Projections
Permitted Discharge Locations
Interceptor Sewers
CSO Locations
FCI Bar Screen
Sewage Treatment Plant No. 1
Pre-treatment Facility
Primary Treatment
Primary Clarifier
Secondary Treatment
Secondary Treatment – Top of Wall
North Secondary Treatment Unit
Blower Building
Chlorination System
Gravity Belt Thickener
Sludge Lagoons
Digester No. 1
Digester No. 2
STP No. 2
STP No. 2 – North Unit
State Street Basin Cleaning Concept
Storm Basin – Option No. 2 Improvements
Sewage Treatment Plant No. 1 – Conventional Activated
Sludge
Counter Current System – Plan View
Counter Current System
Counter Current without Primary Clarifiers
Counter Current System with Primary Clarifiers
SBR in Clear Lake, Iowa
Sequence Batch Reactor (SBR)
Vertical Loop Reactor (VLR) – Section View
Vertical Loop Reactor (VLR)
Vertical Loop Reactor (VLR)
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List of Appendices
Appendix A
Appendix B
Appendix C
Appendix D
Appendix E
Appendix F
Appendix G
Appendix H
Appendix I
Appendix J
Appendix K
Appendix L
Appendix M
NPDES Permit
STP #1 System Component Description
Wastewater System Buildings
STP #1 Historical Operation Data
Primary Clarifier Information
Secondary Clarifier Information
UV System Data
Sludge Thickening and Dewatering Equipment Information
Conventional Activated Sludge System Data
Data on Counter Current System without Primary Clarifier
Data on Counter Current System with Primary Clarifier
Information on Sequence Batch Reactor (SBR) System
Information on Vertical Loop Reactor (VLR) System
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1.0 Summary, Conclusions and Recommendations
The existing wastewater treatment system within the City of Pekin planning area is inadequate to meet the
projected wastewater needs throughout the 20-year planning period. The primary wastewater collection
interceptor sewers appear to be adequate for the planning period based upon the projected growth areas.
The 12 primary wastewater pumping stations throughout the City were previously evaluated by Harding
ESE and the City is currently in the process of upgrading those stations as required for future growth and
operational dependability.
This report provides a summary of pertinent data regarding various City wastewater systems and
evaluates several alternative solutions to meet the wastewater needs of the area for the next 20 years. The
specific wastewater systems included as part of this study are:
•
•
•
•
•
One CSO first flush basin;
Four interceptor sewers;
Four combined sewer outfalls;
One off-site pre-treatment system; and
Two wastewater treatment plants.
An analysis of the CSO first flush basin, located adjacent to the State Street pump station, indicates an
immediate need to improve the basin cleaning system. Three options were evaluated and one has been
selected as the best long-term solution. The estimated cost of the cleaning system is included in Table
1.1. Installation of this system will reduce the need for maintenance staff to enter the underground basin,
reduce the cost of subcontract labor to clean the basin, and improve the quality of combined sewer
overflow at State Street during a storm event.
Projected flow calculations of the four primary interceptor sewers within the City indicate that all have
the capacity to adequately transport the wastewater flow for the next 20 years. These four interceptor
sewers include:
•
•
•
•
Southeast Interceptor;
North Side Interceptor;
South Side Interceptor; and
Northeast Interceptor.
The proper operation of the combined sewer outfalls (CSOs) is critical to protect the City’s combined
sewer system and treatment plant. The CSO structures serve as the gate to allow storm water, combined
with sanitary sewer water, to discharge to the Illinois River during times of significant storm events.
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Table 1.1
Summary of Wastewater Improvement Costs
Description
Combined Sewer Overflows
FCI Pre-Treatment
CSO Settling/CL2 Basin
Sewage Treatment No. 1
Estimated Total Costs
Estimated Capital Costs
$ 101,910
$ 19,000
$ 175,120
$7,023,750
$7,319,780
They also serve as a gate to prevent high Illinois River waters from entering the combined sewer system
and potentially flooding the treatment plant. An inspection of the CSO structures indicates an immediate
improvement need at three of the four structures, at a relatively small cost as shown in Table 1.1.
The Federal Correction Institute (FCI) funded the construction of a preliminary treatment facility located
adjacent to the Pekin FCI facility. Proper operation of this treatment facility is imperative to prevent the
potential plugging of the City’s sanitary sewers and overloading of the treatment plant preliminary
treatment system. The FCI preliminary treatment facility is in good condition with the immediate need of
building repairs and minor component replacements. The cost of these improvements is also included in
Table 1.1.
The City’s two treatment facilities, STP #1 and STP #2, are not adequate to treat the 20-year projected
wastewater loadings. Five options for expanding the treatment capacity have been evaluated in this
report. The selected option has an estimated capital cost of $7,023,800. Based on the evaluation of the
existing treatment facility and the current wastewater loadings, the process of improving and expanding
the treatment plant should be initiated in the immediate future.
The total capital cost of the design and construction for all of the recommended improvements, as listed in
Table 1.1, is approximately $7,320,000. These recommended improvements provide a plan for satisfying
the wastewater treatment and interceptor sewer needs of the planning area for the next 20 years.
Thorough and timely maintenance of all systems will need to be performed to assure the expected life of
the improvements are realized, once the improvements are in place.
This Facilities Plan should be reviewed and updated approximately every five years. The review process
would reflect the actual growth and development that occurred over the previous five years, evaluate the
condition of the wastewater systems to provide data for annual capital improvement budgets and keep the
plan current. Since portions of the proposed improvements are more flow dependent than time
dependent, regular reviews will allow future modifications and improvements to be made at the optimum
time.
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2.0 Introduction
2.1
Study Purpose and Scope
The City of Pekin, Illinois constructed Wastewater Treatment Plant No. 1 (STP #1) shown in Figure 2.1,
in 1939, and completed plant capacity expansions in 1963, 1970 and 1995. Wastewater Treatment Plant
No. 2 (STP #2) shown in Figure 2.2, was built in 1971, and expanded in 1975.
The City initiated wastewater facility planning over 20 years ago to participate in the U.S. Environmental
Protection Agency (USEPA) construction grant
program. In May 1979, the City submitted a
wastewater facility plan document to the Illinois
Environmental Protection Agency (IEPA),
prepared by Kingdom & Naven, Inc. Randolph
& Associates, Inc. later revised the plan
document in response to IEPA requests for
additional information. This supplemental
facility planning information was submitted to
IEPA in May and August 1981.
In the late 1980s, USEPA construction grant
Figure 2.1 - Sewage Treatment Plant No. 1
funding allowed the City to make significant
wastewater collection and treatment
improvements based on the 20-year needs identified in the initial facility plan and the succeeding
supplements. The construction resulted in the completion of an interceptor sewer from STP #2 to STP #1,
revisions of STP #2 – suspending the treatment operation and providing for use of the facility for excess
flow storage, expansion of STP #1 to accommodate the projected 20-year wastewater flow and other STP
#1 improvements.
On November 28, 1990, Harding ESE (then
Environmental Science & Engineering), prepared
a study report entitled “Wastewater Treatment
Facilities Improvements related to the Proposed
Prison Facility.” This report outlined the
improvements required to increase the capacity
of STP #1 to accommodate the Federal
Correction Institute (FCI) – Pekin Facility. The
resulting construction project increased the
treatment system average flow and maximum
flow from 4.1 million gallons per day (MGD) to
4.5 MGD and 7.4 MGD to 8.74 MGD, respectively.
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A “Wastewater Treatment Facility – Preliminary Planning Study” was prepared for the City of Pekin in
January 1997 by Crawford, Murphy & Tilly, Inc. The plan was filed by the City to compliment the 1996
Comprehensive Plan and used as a reference guide for future wastewater treatment expansion planning.
An evaluation of the City’s wastewater collection system main interceptor sewers and the treatment
capacity is again necessitated as a result of higher-than-anticipated wastewater organic loading from the
FBOP facility, increasing commercial and residential development within the City and considerable
annexation to the north, south and east. The following scope items were identified by the City for
Harding ESE to include in the Wastewater Facility Plan:
CSO Area
Corporate
Limits
Planning
Area
Figure 2.3 - Wastewater Planning Area
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•
Project future wastewater characteristics, including hydraulic loading, organic loading, and solids
loading;
•
Evaluate existing and potential local, state and federal regulations and the impact they may have on
the wastewater system;
•
Perform an evaluation of the existing facilities;
•
Identify system improvement options; and
•
Recommend a cost effective improvement plan.
The study conducted in order to prepare this facility plan was comprehensive and included an evaluation
of numerous wastewater system components. The wastewater systems evaluated include the following
components:
•
•
•
Pre-treatment system located at the Pekin-Federal Correction Institute (FCI)
•
Four combined sewer outfalls: State Street, Caroline Street, Court Street, and Fayette Street
•
Five interceptor sewers: South Interceptor, Southwest Interceptor, North Interceptor, Northeast
Interceptor and the Lick Creek Interceptor
•
State Street first flush basin
2.2
Planning Area
The Facilities Planning Area, as described in the City’s 1996 Comprehensive Plan, consists of the current
service area, including the Village of North Pekin and the area within the City’s jurisdictional limits as
shown in Figure 2.3. The planning area identified in the Comprehensive Plan will be used for purposes
of identifying and evaluating the wastewater system expansion.
The planning area includes approximately 24,500 acres, which incorporates the City of Pekin, the Village
of North Pekin, and several unincorporated areas surrounding Pekin. North Pekin and a portion of Pekin
have separate sanitary and storm sewers, while a portion of Pekin, as shown in Figure 2.3, is served by a
combined sewer system.
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3.0 Community Profile
The City of Pekin, Illinois is located along the east bank of the Illinois River, in the west central part of
the State. Two State Highways, Route 29 and 98, intersect in the north part of the City, with State
Interstate 474 located immediately to the north. The City is the seat of Tazewell County and is located 10
miles south of Peoria, Illinois.
Population growth within the City has been modest over the past 30 years. The population was at its
highest in 1980, with a City population of 33,967. A special census performed in 1996 indicated a
population of 33,050. The population in 1999 was estimated to be 33,200, with a projected population
growth rate of 0.5% per year through the year 2015. Population statistics and projections were assembled
in the City’s 1996 Comprehensive Plan and are included in Table 3.1 and Figure 3.1.
Table 3.1
City of Pekin, Illinois
Population Projection
Year
1970
1980
1990
1996 (Special Census)
2000 (projection)
2005 (projection)
2010 (projection)
2015 (projection)
Population
31,375
33,967
32,254
33,050
33,665
34,515
35,387
36,280
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Table 3.2
Wastewater Projections
Year
Flow (MGD)
2000
2005
2010
2015
4.87
5.53
6.18
6.84
BOD Loading
(Pounds/Day)
7,933
9,034
10,118
11,219
TSS Loading
(Pounds/Day)
11,842
13,211
14,560
15,910
The volume of wastewater is also expected to increase in relation to the population, commercial and
industrial growth within the service area. Historical wastewater loading and operation data is included in
Appendix D and was used for future loading projections. For the purposes of evaluating the City’s
wastewater treatment system and its capacity to accommodate the future wastewater volumes, the volume
projections included in the City’s 1996 Comprehensive Plan will be utilized (per the City and Harding
ESE contractual scope of services). The wastewater flow projections are 6.84 million gallons per day
(MGD) design average flow and 15.39 MGD peak hourly flow for the year 2015. These flows are greater
than the existing treatment system design average flow and peak hourly flow of 4.5 MGD and 8.7 MGD,
respectively.
Table 3.2, Figure 3.2, Figure 3.3, and Figure 3.4 list the projected wastewater loadings for flow, BOD5,
and TSS. The loading projections are based on a population growth of 0.5% per year, industrial
wastewater flow increase of 1.0 MGD, and a 0.8-MGD increase of commercial wastewater flow through
2015. The population growth projection was developed in the City’s Comprehensive Plan and the
industrial and commercial wastewater flow increase is based on Public Works Department projections.
37,000
36,000
Population
35,000
34,000
33,000
32,000
31,000
30,000
29,000
28,000
1970
1980
1990
1996
2005
2010
2015
Year
Figure 3.1 - Population Projection
2000
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7
Daily Average Flow (MGD)
6
6.84 MGD
Expanded
Capacity
.
5
4
4.5 MGD
Existing
Capacity
3
2
Figure 3.2 - Hydraulic Loading
2015
2010
2005
1999
1998
1997
1996
1995
1994
1993
1992
0
1991
1
Year
11,219
lbs/day
Expanded
10,000
8,000
6,000
7,506
lbs/day
Existing
4,000
Figure 3.3 - Organic Loading Projection
2015
2010
2005
1999
1998
1997
1996
1995
1994
1993
0
1992
2,000
1991
Daily Average BOD (lbs./day)
12,000
Year
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16,000
14,000
15,910
lbs/day
Expanded
10,000
8,000
6,000
9,383
lbs/day
Existing
4,000
Figure 3.4 - Solids Loading Projections
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2015
2010
2005
1999
1998
1997
1996
1995
1994
1993
0
1992
2,000
1991
Daily Average TSS
12,000
Year
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4.0 Wastewater Effluent Limitations
4.1
NPDES Permit
The City of Pekin currently has two domestic wastewater treatment plants to serve the City of Pekin,
Village of North Pekin, and a portion of the surrounding populated area. Sewage Treatment Plant No. 1
(STP #1) is fully operational, while Sewage Treatment Plant No. 2 (STP #2) is currently being used only
for excess flow storage, with all of the stored wastewater being pumped to STP #1 for full treatment. The
effluent discharged from STP #1 is regulated by the City’s National Pollutant Discharge Elimination
System (NPDES) permit, administered by the Illinois Environmental Protection Agency (IEPA). A copy
of the effective permit, Permit No. IL0034495, is included in Appendix A.
The NPDES permit regulates six discharges throughout the system as listed in Table 4.1 and shown in
Figure 4.1. Outfall 001, located at STP #1, is the treated wastewater effluent discharge to the Illinois
River. Sampling requirements include carbonaceous BOD, suspended solids, fecal coliform, pH, chlorine
residual and ammonia nitrogen. Wastewater flow is to be monitored continuously. The parameter
concentration limits for Outfall 001 are listed in Table 4.2.
Table 4.1
Discharge No.
001
Name/Location
STP Outfall/STP #1
Description
STP #1 effluent discharge
002
Treated Combined
Sewage/STP #1
003
State Street Lift Station
CSO Outfall
004
Caroline Street Overflow
CSO Outfall
005
Court Street Overflow
CSO Outfall
006
Fayette Street Overflow
CSO Outfall
Storm lagoon/chlorination basin
discharge
Outfall 002, located adjacent to STP #1, discharges during rainfall events when the influent flow to STP
#1 exceeds 8.7 MGD. Partial treatment is provided, including settling and chlorination prior to discharge
to the Illinois River. Sampling for BOD5, suspended solids, fecal coliform, pH and chlorine residual is
required on a daily basis during discharge. Discharge flow is to be measured continuously.
Concentration limits have been established for fecal coliforms, pH, and chlorine residual. The current
limits are 400 colonies per 100 mL, 6 to 9 standard units, and 2.0 mg/l, respectively.
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Table 4.2
STP #1 Outfall
Effluent Limits
Load Limits (lbs/day)
Concentration Limits (mg/l)
Monthly
Weekly
Monthly
Weekly
Daily
Average
Average
Average
Average
Maximum
751
1,501
20
40
--938
1,689
25
45
--Daily Maximum shall not exceed 400 per 100 m/l (May-October)
Shall be in the range of 6 to 9 Standard Units
--------0.75
----Report
Report
---
Parameter
CBOD5
Suspended Solids
Fecal Coliform
pH
Chlorine Residual
Ammonia Nitrogen
The treatment requirements for the four combined sewer overflow outfalls listed in the NPDES permit is
“sufficient treatment to prevent pollution and the violation of applicable water quality standards.”
Sufficient treatment is further described in the permit as:
a.
b.
All dry weather flows and the first flush of storm flows shall meet all applicable effluent
standards and the effluent limitations as required for STP #1 outfall 001; and
Additional flows, but not less than ten times the average dry weather flow for the design year,
shall receive a minimum of primary treatment and disinfection with adequate retention time.
Discharge 003
Discharge 005
Discharge 004
Discharge 006
Discharge 001
Discharge 002
Figure 4.1 – Permitted Discharge Locations
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Other CSO outfall requirements include preventing accumulations of sludge deposits, floating debris and
solids in accordance with 35 Ill. Adm. Code 302.203 and to prevent depression of oxygen levels.
4.2
Future and Pending Regulations
Existing and potential future regulations must be taken into consideration as the City prepares for
wastewater improvements during the 20-year planning period. While it is difficult, if not impossible, to
predict what regulations the USEPA and IEPA may enact in the future, the Agency does publish
regulations currently being considered.
Current state regulations that may soon impact the City’s treatment system include the ammonia nitrogen
limit that will be added to the existing NPDES permit once the system reaches a 50,000 population
equivalent (35 Illinois Administrative Code 304.122) and full treatment of the wastewater during the 25year flood (35 Illinois Administrative Code 370.141c.).
Potential future regulations that may or may not impact the City of Pekin include:
The establishment of Proposed Total Maximum Daily Loads (TMDL) for impaired waters, some of
which are yet to be identified.
The potential concentration limit for dioxin and dioxin-like compounds in sewage sludge that is land
applied. (Proposed Rules, Federal Register: December 23, 1999; 40 CFR Part 503).
Upcoming revised aquatic life criteria for copper, silver, lead, cadmium, iron, and selenium and the
development of aquatic life criteria for atrazine, diazinon, nynylphenol, methyl tertiary-butyl ether
and manganese.
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Harding ESE, Inc.
5.0 Current Wastewater System
5.1
Wastewater Collection
The City’s initial wastewater collection system, comprised of combined sewers, was reportedly installed
in 1905. Combination sewers were constructed until 1929 when the practice of constructing one sewer
for both sanitary and storm water was ended. Since that time, separate sewers were installed for the
sanitary wastewater and storm water, but many of the sanitary sewers discharge into interceptors that also
receive combined sewer discharge.
The City has actively pursued separation of the combined sewers and are currently evaluating other
potential sewer construction projects to further reduce the number of combined sewers in the system.
Further sewer separation will result in less overflow to the river, lower flow rates to be treated at STP #1
during periods of rainfall, and fewer sewer backups during storm events.
5.2
Wastewater Treatment
The City currently has two wastewater treatment facilities. Wastewater Treatment Plant No. 1 (STP #1),
originally constructed in 1939, has been expanded several times, with the latest expansion in 1995. STP
#1 is currently rated at 4.5 MGD average flow and 8.74 MGD maximum flow. Wastewater Treatment
Plant No. 2 (STP #2), built in 1971 and expanded in 1975, is a 1MGD plant and currently used only for
excess flow storage. STP #2 was removed from service following completion of improvements to STP
#1 in 1989 and the construction of a new interceptor sewer (North Side Interceptor) from STP #2 to STP
#1.
The existing STP #1 is designed to treat up to 7,506 pounds-per-day (ppd) of biochemical oxygen demand
(BOD5) and up to 9,383 ppd of total suspended solids (TSS). These ratings reflect raw sewage
concentrations of 200 parts-per-million (ppm) BOD5 and 250 ppm TSS at a design average flow of 4.5
MGD.
In 1995, the plant loadings were the highest recorded in the last 10 years when the average flow, BOD5
loading and TSS loading were equal to or exceeded the rated plant capacity. The average flow, BOD5
loading, and TSS loading for 1995 were 4.5 MGD, 7,532 ppd, and 9,815 ppd, respectively. Based on the
past 5-year average loadings (1995-1999), the plant utilization for flow, BOD5, and TSS was 86.7%,
82.5%, and 87.1%, respectively.
The historical plant loadings since 1991 for STP #1 and the plant permitted loadings are listed in Table
5.1.
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Harding ESE, Inc.
Table 5.1
Historical Treatment Plant Loadings
Daily Average Values
Year
Flow (MGD)
1991
1992
1993
1994
1995
1996
1997
1998
1999
Design
Loadings
3.7
3.7
4.8
3.8
4.5
4.0
3.6
3.8
3.6
4.5
Percent
of
Design
82
82
107
84
100
89
80
84
80
---
BOD Loading
(Pounds/Day)
3,210
3,370
4,242
4,984
7,532
6,046
6,436
5,291
5,662
7,506
14
Percent
of
Design
43
45
57
66
100
81
86
70
75
---
TSS Loading
(Pounds/Day)
5,403
6,524
6,960
8,604
9,815
7,618
9,009
7,785
6,635
9,383
Percent
of
Design
58
70
74
92
105
81
96
83
71
---
Harding ESE, Inc.
6.0 Wastewater System Evaluation
6.1
Interceptor Sewers
The following interceptor sewers are being evaluated for capacity to accommodate existing and future
wastewater flows.
•
Southeast Interceptor
•
North Side Interceptor
•
South Side Interceptor
•
Northeast Interceptor
6.1.1
Southeast Interceptor
The southeast interceptor shown in Figure 6.1, connects to STP #1 from the south on Front Street. The
pipe size ranges from 21 inches to 27 inches at the inlet to the plant. The rated capacity of the southeast
interceptor sewer is 5.15 MGD, based on a pipe size of 27 inches, minimum slope of 0.067 feet/100 feet,
and a velocity 2.0 feet-per-second (fps). This rated capacity also assumes a clean pipe free of debris. The
estimated average flow for the interceptor is 0.285 MGD based on present flows, with an estimated
maximum flow of 0.92 MGD.
Based on the estimated existing flows, the southeast interceptor can accommodate an additional 4 MGD
maximum flow.
The City is addressing an issue raised by IEPA concerning a potential outfall leading to the Illinois River.
Televising and dye testing is currently being performed by the City to determine where the potential
outfall is located.
6.1.2
North Side Interceptor – STP #2 to STP #1
The North Side Interceptor, installed in 1987, transports wastewater from North Pekin’s forcemain and
the north and east side of the City of Pekin to the STP #1 Junction Box, as shown in Figure 6.2. The City
of Pekin and the Village of North Pekin wastewater flows combine at the STP #2 diversion chamber and
flow through a 27-inch ribbed polyethylene pipe to a 30-inch RCP to a 30-inch ductile iron pipe to STP
#1.
The current estimated average flow through the North Side Interceptor is 1.63 MGD, with an estimated
design maximum flow of 2.94 MGD. The estimated capacity of the 30 inch interceptor is 6.36 MGD,
which allows for significant future flow increases. The estimated capacity is based on 30 inch RCP,
minimum slope of 0.058 feet/100 feet, a velocity of 2.0 fps, and a clean pipe free of debris.
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Harding ESE, Inc.
North Side
North East
South East
South Side
Figure 6.1 – Interceptor Sewers
6.1.3
South Side Interceptor
The south central portion of the City of Pekin discharges wastewater into the 24-inch South Side
Interceptor. The estimated capacity of the interceptor at the discharge is 4.09 MGD, based on a minimum
slope of 0.08 feet/100 feet, a velocity of 2.0 fps, and a clean pipe free of debris.
The estimated average flow for the interceptor is currently 0.96 MGD, with a 1.80 MGD maximum flow.
Based on these estimates, the South Side Sewer has a remaining design maximum flow capacity of 2.29
MGD.
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Harding ESE, Inc.
6.1.4
Northeast Interceptor
The north and east portions of the City of Pekin discharge their wastewater into the 27-inch Northeast
Interceptor. The current average flow is estimated to be 1.4 MGD, with a maximum flow of 2.5 MGD.
The 27-inch interceptor has an estimated design maximum flow capacity of 5.15 MGD. This estimated
capacity is based on a 27-inch pipe, minimum slope of 0.067 feet/100 feet, a velocity of 2.0 fps, and a
clean pipe free of debris.
6.1.5
Impact of Lick Creek Interceptor
The Lick Creek Interceptor sewer connects to the North Side interceptor at the STP #2 diversion chamber.
According to information provided by Maurer-Stutz, Inc., the design engineers for the Lick Creek
Interceptor, the projected design average flow and peak flow is 0.86 MGD and 2.84 MGD, respectively,
including an allowance for I/I. As discussed in Section 6.1.2, the North Side interceptor currently has an
excess capacity of 3.42 MGD within the 30-inch sewer and approximately 2.21 MGD within the 27-inch
sewer at peak flows. Peak flows should be monitored within the North Side interceptor as the Lick Creek
Interceptor becomes more fully utilized to prevent surcharging the 27-inch interceptor.
6.2
Combined Sewer Overflow (CSO) Structures
The City of Pekin’s combined sewer system includes four combined sewer overflow structures. The
overflows are included in the City’s NPDES permit as permitted outfalls to the Illinois River. Table 6.1
includes the discharge number, name, and brief description. Figure 6.2 shows the general location of each
CSO structure and discharge point.
Table 6.1
Discharge No.
003
004
005
006
Name/Location
State Street Lift Station
Caroline Street Overflow
Court Street Overflow
Fayette Street Overflow
Description
60-inch CSO Outfall
36-inch CSO Outfall
54-inch CSO Outfall
60-inch/54-inch CSO Outfall
All of the CSO structures were improved in 1987 –1988. This improvement project included the addition
of control gates, structure repairs, and sewers connecting each structure to the North Side interceptor.
6.2.1
Fayette Street Outfall
The Fayette Street Outfall connects to both the North Side and “old” interceptor sewers, similar to the
other three CSOs, and to a 60-inch combined sewer on Fayette Street. When the flow in the 60-inch
combined sewer exceeds the sewer capacity connected to the interceptors, the excess flow, during wet
weather conditions, discharges to the Illinois River through a 60-inch flap gate and 54-inch discharge
pipe.
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Harding ESE, Inc.
State Street
CSO
Court Street
CSO
Caroline Street
CSO
Fayette Street
CSO
Figure 6.2 – CSO Locations
The outfall pipe and concrete headwall are both in good condition. The outfall structure walls are in good
condition, but the concrete top is cracked. The cover is difficult to access since it is located in the street.
The 15-inch and 18-inch slide gates located on the sewers that drain to the “old” and North Side
interceptors are inoperable. The 60-inch flap gate is in good condition.
6.2.2
Court Street Outfall
The regulator structure is connected to the North Side interceptor sewer by a 15-inch sewer and to the
“old” interceptor sewer by a 30-inch sewer. When the flow exceeds the capacity of the connecting
sewers, it overflows the fixed weir and drains out to the river through a 54-inch outfall pipe. The two
sewers are equipped with sluice gates and the outfall is equipped with a flap gate.
The CSO concrete headwall is in good condition. The concrete regulator chamber is in fair to poor
condition with exterior deterioration, especially on the structure ends. The slide gates located on the
“old” and North Side interceptors appear to be in good condition, but the operators will only slightly
move the gates. The effluent pipe penetration into the structure needs to be resealed.
6.2.3
Caroline Street Outfall
A 36-inch combined sewer discharges into the regulator chamber. The regulator chamber is connected to
the North Side interceptor by a 12-inch sewer and the “old” interceptor by a 21-inch sewer. During wet
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Harding ESE, Inc.
weather conditions, the influent flow will exceed the capacity of both the 12-inch and 21-inch sewers and
overflows the fixed weir. This overflow drains to the river through the 36-inch outfall pipe.
The outfall headwall and pipe are in good condition and the 36-inch tube valve appears to be in good
condition. The sluice gates located on the sewers flowing to the “old” and North Side interceptors appear
to be in fair condition, but the gates were inoperable. The regulator chamber is in good condition.
6.2.4
State Street Outfall
A 60-inch combined sewer drains into the State Street pump station during dry weather conditions.
During periods of wet weather, when the pump station is not able to pump all of the incoming flow, the
excess flow is diverted into the first flush basin. When the basin level reaches the discharge weir, the
overflow drains into the 60-inch outfall. A 60-inch flap gate prevents the river from backflowing into the
basin and combined sewer. There is also a 60-inch sluice gate that can be closed if the flap gate should
fail to seal.
The outfall headwall is in good condition, as are the sluice gate and the flap gate.
6.3
State Street First Flush Basin
The State Street CSO Basin is an underground concrete tank that stores overflows from the State Street
combined sewer during wet weather conditions. If the volume exceeds the capacity of the tank, it flows
into the effluent channel and out to the Illinois River. Due to the nature of combined sewage, a
significant quantity of solids accumulates in the bottom of the tank when the tank is storing excess flow.
Traditionally the City has used a local firm to remove the solids from the tank on a periodic basis.
Cleaning the tank in this fashion is difficult and dangerous due to limited access, potentially harmful
gases, and poor ventilation. Options to improve the solids removal are evaluated in Section 7.2.
6.4
Federal Corrections Institute (FCI)
The FCI bar screen facility, as shown in Figure
6.3, constructed in 1994, includes a masonry
building, bar screen room with a Parkson stainless
steel mechanical bar screen, a control room which
houses the electrical controls, flow meter,
automatic sampler, a through-the-wall HVAC
system, and an emergency engine-generator. The
building floor was constructed approximately two
feet below grade so stairs have been installed to
provide access to the building. A concrete ramp
provides access to the bar screen room for
removal of the waste-filled dumpsters.
19
Figure 6.3 - FCI Bar Screen
Harding ESE, Inc.
The bar screen room walls are in good condition. Due to the sewer gases in the bar screen room, all of the
metal fixtures, roof components, stairway, etc. are corroded. The control room components have also
been impacted by the sewer gases. The interior roof/wall seals are in poor condition. The portable
engine-generator is in good condition.
6.5
Sewage Treatment Plant No. 1 (STP#1)
A condition evaluation was performed on STP #1, based on several site visits, prior knowledge of the
facility, and discussions with City and United Water staff. This report section includes a general
description of each system, a summary of the system’s condition, and a projection of the remaining useful
life of each component. A listing of treatment plant components is included in Appendix B and a general
site plan is included as Figure 6.4.
6.5.1
6.5.1.1
Pretreatment Facility
General Description
The existing wastewater pre-treatment facility, shown in Figure 6.5, includes a mechanically-cleaned bar
screen, an aerated grit chamber with grit washer system, and a channel grinder. Prior to the pre-treatment
facility are electrically-operated gates capable of directing influent flow to either the bar screen or the
channel grinder and of regulating the rate of flow entering the plant. At normal flows, the influent is
directed to the bar screen. At higher flows, the wastewater is routed to the channel grinder. All flows
enter the aerated grit chamber, which is rated by the manufacturer for maximum sewage flows of up to
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Harding ESE, Inc.
5.7 MGD. IEPA’s design criteria for aerated grit removal systems requires a detention time of no less
than three minutes at peak flow. The existing grit chamber has a theoretical detention time of 4.13
minutes at a flow rate of 8.74 MGD. Actual operational experience has shown that theoretical detention
times do not always occur, and it is entirely possible that much shorter detention times are prevalent
during peak flows allowing grit to enter the primary treatment system. The grit washer, housed in the Grit
Building, is appropriately sized for the plant’s rated flow and was installed in 1999.
6.5.1.2
Condition Evaluation
The overall condition of the pre-treatment system is fair. The building is in good condition with minor
improvements required, including the installation of a second unit heater, replacement of lights, doors,
gutters and downspouts (other building improvements have been identified by United Water and City
staff and the list is included in Appendix C). The electric slide gates installed in 1998 are in good
condition and can operate automatically, electrically in hand mode, or manually by utilizing the
handwheels mounted on the operators. The channel grinder is also in good condition, as a result of a
rebuild in 1999. The bar screen is original equipment, installed in 1981-1982, and is near the end of its
useful life. The bar screen needs to be replaced with an updated unit. Designs to reduce the flow
fluctuations into the primary treatment system, that result from wastewater backup behind the bar screen
between screen cleanings should be considered. The grit removal system is also original equipment,
installed in 1981-1982, and is in fair condition. The grit tank requires periodic cleaning and will need to
have the handrails and walkway system replaced in the near future. As stated previously, the grit washer
was replaced in 1999 and is in very good condition. Due to the limited effectiveness of the aerated grit
removal system at flow rates exceeding 5.7 MGD, a second system should be added for adequate grit
removal during periods of high flows. Additional condition information is listed in Table 6.5.1.
Figure 6.5 - Pre-treatment Facility
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Harding ESE, Inc.
Table 6.5.1
Pre-treatment System
Condition Summary
Item Description
Condition
Electric Slide Gates
Bar Screen
Channel Grinder
Good
Fair
Good
Useful Life
Remaining
(years)
15
2
15
Aerated Grit System
Fair
10
Aerated Grit Tank
Grit Tank
Walkway/Handrails
Grit Washer
Building Interior
Fair
Fair
15
2
Good
Good
20
15
Building Exterior
Good
15
6.5.2
6.5.2.1
Comments
New in 1998
End of useful life
Will require routine maintenance, repairs
and cutter replacement
Air and grit piping and pump will need
repaired/repainted
Periodically requires cleaning
Walkway and handrails need to be
replaced
New in 1999
Additional unit heater and light
replacement needed
Lights, gutters, downspouts, and
mandoors need to be replaced
Primary Treatment
General Description
The primary treatment system, shown
in Figure 6.6, removes grease and
scum using a surface skimmer system.
Sludge is removed by two positive
displacement sludge pumps. The
clarifiers provide 7,932 square feet of
surface area, with a total volume of
68,947 cubic feet, or 515,724 gallons.
Figure 6.6 - Primary Treatment
The primary clarifiers provide settling
for the pre-treated wastewater. The clarifier surface area, based on IEPA design criteria for BOD removal
at surface settling rates of 1,200 gpd/sq. ft., will allow for peak flow of 9.5 MGD.
The existing primary treatment facility includes a flow splitter box, four circular clarifiers and primary
sludge removal. The concrete flow splitter box divides the incoming flow from the 30-inch RCP influent
line to a 14-inch RCP line that feeds clarifier No. 1 and No. 3 and to an 18-inch RCP line that feeds
clarifier No. 2 and No. 4. Two clarifiers, the northwest (No. 3 clarifier) and southwest (No. 1 clarifier),
built in 1939, and upgraded in 1974, are each 45 feet in diameter. The other two clarifiers, known as the
northeast (No. 4) and the southeast (No. 2), constructed in 1963, are each 55 feet in diameter.
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Harding ESE, Inc.
The existing primary sludge pumps are air-operated diaphragm units each rated at 180 gpm at 52 feet of
head. A sludge grinder is located on the inlet piping of the sludge pumps. The buried sludge piping from
the clarifiers to the sludge pumps contains isolation valves for each clarifier. A duplex air compressor
system is housed in the control building to provide the 50 SCFM of air required for operation of one
sludge pump, an adequate supply for sludge pumping operations.
6.5.2.2
The following discussion provides a condition description of the primary treatment components. A
summary of the component condition is listed in Table 6.5.2.
Flow Splitter
The concrete flow splitter box is in good condition with minor cracks and surface deterioration. The
influent and effluent pipes appear to be in good condition. Minor maintenance is required to prevent
accumulation of solids in the box. The slide gates within the flow splitter box are in poor condition.
Table 6.5.2
Primary Treatment System
Condition Summary
Item Description
Condition
Flow Splitter Box
Flow Splitter Box
No. 1 – 45’ Clarifier
Sludge Piping
Sludge Pumps
Good
Poor
Fair
Fair
Fair-Poor
Fair
Poor
Good
Useful Life
Remaining (years)
10
0
5
10
5
10
2
15
Air Compressor No. 1
Air Compressor No. 2
Sludge Grinder
Control Building
Poor
Good
Good
Good
0
10
10
20
23
Comments
Routine maintenance required
Inoperable
Drive replaced in 1998
Walkway/handrails – poor
Concrete cracked
Walkway/handrails -poor
Needs replaced
Air solenoid and diaphragm
require routine maintenance/
replacement
Currently being replaced
New in 2000
Recently rebuilt
Basement leaks groundwater;
sump pumps in poor condition
Harding ESE, Inc.
Primary Clarifiers
Clarifier No. 1
The 45-foot diameter No. 1 primary clarifier is located in the southwest corner of the clarifier system, as
shown in Figure 6.4, and is in fair condition with an estimated useful life of 5-years. This clarifier was
installed and upgraded at the same time as clarifier No. 3, approximately 60 years and 26 years ago,
respectively. The concrete structure has obvious cracks and surface deterioration, with the wall adjacent
to the sludge pit in poor condition. The drive unit was replaced approximately two-years ago with a new
Walker Process drive and is in good condition. The scraper and skimmer systems were inspected by
Walker Process when the drive unit was replaced and reported to be in fair to poor condition. The metal
walkway and handrails have been painted and are in fair condition, but will require some minor repairs
and repainting in 2-3 years. The fiberglass weirs and baffles are approximately five years old and in
good condition. The sludge pit telescoping valve does not seal properly and needs to be replaced.
Clarifier No. 2
Primary clarifier No. 2 is a 55-foot diameter EIMCO clarifier system shown in Figure 6.4 and was
installed in 1963. The No. 2 and No. 4 clarifiers are identical units, installed during the same project.
The No. 2 clarifier is located in the southeast corner of the clarifier system. It is in fair condition with an
estimated useful life of 10 years. The concrete structure has surface cracks and deterioration. The 37year old EIMCO drive, skimmer and sludge scraper systems are in fair condition. The fiberglass weirs
and baffles are in good condition. Similar to clarifier No. 4, the painted metal walkway and handrail
system is in poor condition, requiring significant repairs within the next two years. The sludge pit
telescoping valve does not seal properly and needs to be replaced.
Clarifier No. 3
The 45-foot diameter No. 3 primary clarifier
located in the northwest corner of the clarifier
system as shown in Figure 6.4 is in fair to poor
condition with an estimated useful life of five
years. The clarifier is approximately 60 years old
with an upgrade completed 26 years ago. The
concrete structure has significant cracks and
deterioration as shown in Figure 6.7, with the wall
adjacent to the sludge pit in poor condition. The
Walker Process drive unit has been in service for
Figure 6.7 - Primary Clarifier
26 years and is in poor condition. The fiberglass
weirs and baffles are approximately five years old and in good condition. The metal walkway and
handrails have been painted and are in fair condition with some minor repairs and repainting required in
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Harding ESE, Inc.
2-3 years. United Water staff advised Harding ESE during the site investigation that the sludge scrapers
are in poor condition. The sludge pit telescoping valve does not seal properly and needs to be replaced.
Clarifier No. 4
The No. 4 primary clarifier, installed in 1963, is a 55-foot diameter EIMCO system. The clarifier is
located in the northeast corner of the clarifier system, as shown in Figures 6.4, and is in fair condition
with an estimated useful life of 10 years. The concrete structure has apparent cracks on the south side
with some surface deterioration throughout the visible portion of the structure. The EIMCO drive has
been in service for 37 years and is in fair condition. The skimmer system and sludge scraper system are
reportedly in fair condition. The fiberglass weirs and baffles are in good condition, having been in
service for five years. The painted metal walkway and handrail system is in poor condition, requiring
some significant repairs within the next two years. Similar to the other three clarifiers, the sludge pit
telescoping valve is in poor condition.
Sludge Piping
Sludge is pulled from the primary clarifiers and/or the sludge pit through a series of underground pipes to
the basement of the control building where the sludge pumps are located. The clarifier isolation valves
located in manholes adjacent to the primary clarifiers, are in poor condition making it difficult to isolate a
single clarifier for sludge removal. The buried sludge piping is also in poor condition with several leaks
being repaired in the last few years. The piping and isolation valves require replacement in the next 1-2
years.
Sludge Grinder
The sludge grinder, installed in the early 1990s is in good condition. United Water staff recently had the
unit rebuilt after nearly 10 years of service.
Sludge Pump System
The air operated diaphragm pumps are also in good condition and should have over 15 years of useful life
remaining. The pump system is a duplex system, so if one pump is out of service the other pump can
handle the sludge pumping. The air solenoids require periodic rebuilding and the diaphragms will
require replacement prior to the expected remaining 15 years of pump life.
Air Compressor No. 1, installed in the early 1990s has recently failed and is currently being replaced. Air
Compressor No. 2, installed after No. 1 failed, is in good condition and should have a useful life of 10 or
more years. With two air compressors operating as a duplex system, a 20-year useful life for the system
could be expected.
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Harding ESE, Inc.
6.5.3
6.5.3.1
Primarily Effluent Pumping
General Description
The primary effluent from the four clarifiers flows by gravity to two pump stations through a 30-inch line.
The first pump station, shown in Figure 6.4 as Pump Station No. 1, contains three 20-horsepower
submersible sewage pumps. The check valves and shut off valves for the three pumps are located in the
basement of the control building. The second pump station shown as Pump Station No. 2, contains two 20horsepower submersible sewage pumps identical to the three in Pump Station No. 1. A separate
underground valve vault contains the check and shut off valves for the two pumps.
Pump station No. 1 and No. 2, with all pumps operational, are rated for a total of 12.4 MGD. The system
with one pump out of service is rated for 9.5 MGD. A spare pump is available should a pump fail and
need to be replaced.
6.5.3.2
The primary pumping system was upgraded in the early 1990s with all the pumps, valves and controls
being replaced. Since that time, the pumps have been rebuilt including replacement of the pump seals.
The system should have 10-15 years of useful life remaining.
6.5.4
6.5.4.1
Secondary Treatment
General Description
The primary effluent is pumped by the effluent pumping system, described in Section 6.5.3, into a 24inch RCP forcemain to a split flow chamber. The split flow chamber constructed in the late 1980s is
equipped with slide gates that provide flow regulation to each of the three secondary treatment units. The
chamber allows for operation of the secondary treatment system in either conventional or contact
stabilization mode. During periods of dry weather and low flows, one secondary treatment unit is
removed from service. All three secondary treatment units are required to be in service during periods of
wet weather.
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Harding ESE, Inc.
Figure 6.8 - Secondary Treatment
The existing secondary treatment facilities, shown in Figure 6.8, are comprised of three secondary
treatment units. Two of the units, constructed in 1970, shown as the South Secondary Treatment Unit and
the North Secondary Treatment Unit in Figure 6.4, are circular, multi-compartment tanks, 120 feet in
diameter. The South Secondary Treatment Unit is divided into contact aeration, re-aeration, 70-foot
diameter clarifier, chlorine contact, and a waste-activated sludge holding tank used for all three secondary
treatment systems. The North Secondary Treatment Unit is divided into contact aeration, re-aeration, 70foot diameter clarifier, chlorine contact and contact aeration and re-aeration for the third secondary
treatment system. The third secondary treatment system, shown as Clarifier No. 3 in Figure 6.4,
constructed in 1995 includes a 70-foot diameter clarifier, chlorine contact, and a return and waste
activated sludge pumping building. Located north of the North Secondary Treatment Unit is the Blower
Building that houses two engine-driven positive displacement blowers, one electrically-driven positive
displacement blower, and the chlorination systems for all three secondary treatment units. Additional
secondary treatment system equipment details are included in Appendix B.
IEPA design criteria for an aeration system requires a design loading rate of 50 lbs. BOD per day per
1000 CF of tank volume (contact and re-aeration combined), 1500 CF of air per lb. of BOD, return sludge
pumps capable of 15% - 100% of peak flow, waste sludge pumps capable of at least 25% of peak flow,
and air piping sized for 200% of the normal requirements. The blower capacity must be adequate to
maintain 2.0 PPM minimum dissolved oxygen level with the largest blower out of service. Design
criteria for secondary settling facilities requires a design surface loading rate of not more than 1000
gallons per square foot per day. Solids loading cannot exceed 50 lbs. per day per square foot at peak
flow. Based on these criteria, the secondary treatment system has the theoretical capability of treating
well over the 4.5 MGD design average flow and 8.7 MGD peak hourly flow.
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Harding ESE, Inc.
6.5.4.2
The secondary treatment system is comprised of components constructed at various times. As a result,
the condition of certain parts of the system are good with others being in fair to poor condition. A
summary of the components condition is listed in Table 6.5.3 and a more thorough description is included
below.
Table 6.5.3
Secondary Treatment System
Condition Summary
Item Description
Condition
Split Flow Chamber
South Secondary Treatment
Unit
Good
Fair
Useful Life
Remaining (years)
15
5
North Secondary Treatment
Unit
Fair
5
FCI Secondary Treatment
Unit No. 3
Good
20
Blower System
Fair
2
Chlorination System
Good
5
Comments
Sealing and repainting required
Significant concrete
deterioration
Traveling bridge near the end of
useful life
Significant concrete
deterioration
Traveling bridge near the end of
useful life
Most components in good
condition
Aeration tanks have significant
concrete deterioration
Blowers are 30-years old
G342 engine’s are obsolete
W-T equipment is outdated
Split Flow Chamber
The split flow chamber, constructed in the late 1980s is in good condition with some minor repairs
required in the near future. The exterior concrete walls have some significant cracks. The sandblast
procedure used to remove the original paint has exposed the aggregate in the concrete making it
susceptible to freeze and thaw damage. The painted steel walkway, handrails, slide gate operators, and
structural supports are beginning to show signs of surface rust.
South Secondary Treatment Unit
The 120-foot diameter tank perimeter walls are in poor condition. They have numerous cracks and areas
of deteriorated concrete. The area on top of the wall where the traveling bridge drive wheels track, shown
in Figure 6.9, was resurfaced approximately 8-10 years ago. This material has cracked and is now
separating from the concrete.
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Harding ESE, Inc.
The contact aeration and re-aeration tanks are in fair
condition. The fine bubble air diffusers, vertical air
piping, and valves were replaced in 1988. More recent
improvements include replacement of the fine bubble
air diffusers in 1999. The six inch air lift sludge pump
is also in fair condition.
The 70-foot diameter clarifier is in fair condition. The
traveling bridge collector mechanism is original
equipment and has been in service for nearly 30 years.
Figure 6.9 - Secondary Treatment - Top of Wall
Maintenance and repairs has kept the system
operational, but it is reaching the end of its useful life. The 12-inch air lift sludge pump is in fair
condition and is also original equipment. The return sludge suction tubes and scraper mechanisms were
replaced in the early 1990s and appear to be functioning adequately. The weirs and baffles appear to be
in good condition.
The chlorine contact zone, including the air diffuser piping, chlorine dispersion piping and baffle system
is in good condition. The chlorine contact zone components were rebuilt in the early 1990s.
If major concrete structure improvements are made in the next year, the South Secondary Treatment Unit
has an estimated useful life of five years.
North Secondary Treatment Unit
The North Unit shown in Figure 6.10, is in nearly
the same condition as the South Unit described
above. The main exception is the contact aeration
and re-aeration tanks for secondary treatment
system No. 3. These tanks are part of the original
1970 construction, but were renovated in 1995.
The fine bubble air diffusers, vertical air piping,
and valves were installed as part of that
renovation and are in good condition. The fine
bubble diffusers will most likely require
replacement in the next two years.
Figure 6.10 - North Secondary Treatment Unit
The North Secondary Treatment Unit has an estimated useful life of five years, assuming major concrete
structure improvements are made within the next year.
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Harding ESE, Inc.
Secondary Treatment Unit No. 3
The contact aeration and re-aeration tanks are a portion of the North Secondary Treatment unit and are
discussed in that report section. Clarifier No. 3, constructed in 1995, is in good condition and has
remaining estimated useful life of 20 years.
Blower System
The three existing blowers, installed in 1970, are
rated at 3,500 CFM each. Caterpillar G342-NA-6
cylinder natural gas engines drive two of the
blowers. Caterpillar has rebuilt the engines, but no
longer manufacture the G342. The third blower is
driven by a 200 HP, 480VAC electric motor which
was replaced in 1990. The blowers are in fair to
poor condition and exhibit significant bearing noise.
The blowers have been in service for 30 years. They
should be replaced in the next 1-2 years or sooner.
Figure 6.11 - Blower Building
The Blower Building shown in Figure 6.11, was also constructed in 1970 and is in fair condition. United
Water and the City of Pekin have developed a list of required building improvements, included in
Appendix C for reference.
6.5.5
Effluent Disinfection
The chlorination system, housed in the Blower Building, is in good condition. The automatic chlorinators
for the North and South Secondary Treatment Units, shown in Figure 6.12, were replaced in the early
1990s. The Secondary Treatment Unit No. 3
automatic chlorinator was installed in 1995. The
manual chlorinators used to control filamentous
bacteria in the aeration system are also in good
condition. The chlorination system has
approximately five years of useful life remaining.
6.5.6
6.5.6.1
Sludge Handling/Processing
General Description
Figure 6.12 - Chlorination System
Historically, the sludge handling facilities at STP #1 have consisted of liquid sludge storage lagoons. In
1989, a gravity belt thickener, vacuum sludge drying beds, sludge storage pad, and associated piping,
controls and metering equipment were added for sludge handling.
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Harding ESE, Inc.
Currently, United Water operates the gravity belt thickener, shown in Figure 6.13, for thickening both
primary and waste activated sludge prior to digesting the sludge in the anaerobic digesters. The vacuum
sludge drying beds and the sludge storage pad are currently not in use. The liquid sludge is stored in the
sludge storage lagoons and then land applied.
A general sludge handling/processing
component description follows, with
specific details listed in Appendix B.
The liquid sludge storage lagoons are
estimated to hold approximately
272,600 cubic feet of sludge (2,039,000
gallons). Sludge can be gravity drained
from Digester No. 1, 2, and 3 to the
lagoons.
The gravity belt thickener (GBT)
system consists of a 2.5 meter wide
Figure 6.13 - Gravity Belt Thickener
gravity belt sludge thickener installed in
1989. Associated components include a 2 GPH variable rate polymer feed system, a 60 GPM rotary lobe
thickened sludge pump, waste activated sludge flow meter, and a PLC-based control system. The GBT
system is capable of thickening sludge at the rate of approximately 250 GPM. The GBT capacity is
limited by the thickened sludge discharge pump.
The waste activated sludge (WAS) pump, housed in the “old dewatering building” pumps the WAS from
the south tank of the South Secondary Treatment Unit to the GBT. The pump is rated at 300 GPM and is
controlled by a variable speed drive.
The vacuum drying bed system is capable of dewatering up to 24,000 gallons of digested sludge in one
cycle. The application and drying cycle time typically ranges from 24 to 48 hours. The system consists
of four 20-foot by 40-foot rectangular vacuum drying beds, an 8 GPH variable rate polymer feed system,
two vacuum pumps, digested sludge flow meter, and a PLC-based control system all housed in the Drying
Bed Building shown in Figure 6.4.
To accommodate storage of the dried sludge, a sludge storage pad was constructed in 1989. The
uncovered storage pad consists of one 60-foot by 100-foot rectangular concrete pad with curbs and drains.
The pad can hold approximately 18,000 CF of dried sludge.
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Harding ESE, Inc.
6.5.6.2
The following paragraphs include a description of the sludge handling/processing components condition
as noted during the STP#1 site investigations performed by Harding ESE personnel. Summaries of the
conditions are listed in Table 6.5.4.
Table 6.5.4
Sludge Handling/Processing
Condition Summary
Item Description
Condition
Sludge Lagoons
Fair
Good
Useful Life
Remaining (years)
--10
Polymer Feed System
Thickened Sludge
Discharge Pump
Waste Activated Sludge
Pump
Good
Good
10
10
Fair
10
Vacuum Bed System
Sludge Storage Pad
-----
-----
Comments
Routine Berm Repair Required
Hydraulic system, belt and moving
parts require periodic maintenance
and replacement
Installed in 2000
Pump replaced in 2000
Has been in service 11 years.
Duplex system should be
considered
Out of service
Out of service
Liquid Sludge Storage Lagoons
The digested liquid sludge stored in the sludge lagoons, shown in Figure 6.14, is periodically removed by
mechanical pumping. The lagoons have not been completely drained and cleaned for many years. Dried
sludge deposits are dispersed throughout the lagoon area. The lagoon berms are in fair condition,
requiring routine maintenance to eliminate rodents and vegetation control. There has historically been a
question regarding groundwater intrusion into the lagoons, especially during periods of high river levels,
indicating a lagoon floor with potentially minimal integrity.
The gravity belt thickener (GBT) was installed in 1989 and is used on a daily basis. The belt has been
replaced several times and other system components have been repaired or replaced. The hydraulic drive
unit and all moving parts are susceptible to wear and require periodic maintenance and replacement.
Based on the site investigation, it appears that the unit will require complete replacement within
approximately 10 years. The vinyl curtain system is in fair condition and will need to be replaced in
approximately five years. The concrete floor and curbing are in good condition.
The system control panel is discussed in Section 6.5.8.
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Harding ESE, Inc.
Figure 6.14 - Sludge Lagoons
Polymer Feed System
The GBT utilizes polymer to enhance the sludge dewatering process. The polymer-feed system has been
in service for 11 years. Due to the importance of the GBT system for the sludge handling/processing
procedure, the City has installed a second polymer feed unit to provide a duplex system. The original unit
will need to be replaced within the next five years.
Thickened Sludge Discharge Pump
The 11-year-old pump is currently being replaced with a new unit. The existing motor is being reused.
As noted in a early 1990 Harding ESE report, the sludge processed by the GBT system is restricted due to
the capacity of the sludge discharge pump. The previous recommendation, which is still valid, is to
replace the existing 60 GPM pump with a 75-100 GPM unit with a higher head capacity.
Waste Activated Sludge Pump
The 300 GPM waste activated sludge (WAS) pump has also been in service for eleven years. It appears
to be in good condition. As with the other GBT support systems, addition of a duplex pump should be
considered. The pump could be installed adjacent to the existing WAS pump in the “old dewatering
building.”
Vacuum Bed System
The vacuum bed system is not being used by United Water. It has been taken out of service due to the
labor required to process the sludge, clean the beds prior to the next sludge application and the variations
in sludge quality and cycle time. The system appears to be in good condition, although the vacuum plates
are showing signs of wear.
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Sludge Storage Pad
The sludge storage pad is also not being used. The pad appears to be in good condition, but a roof should
be installed if it is returned to service for dried sludge storage.
6.5.7
6.5.7.1
Anaerobic Digestion
General Description
The existing anaerobic digester system consists of two primary digesters, a secondary digester, an “old”
out of service digester, gas recovery and conditioning equipment, and electrical controls.
The primary digesters, Digester No. 1 and No. 2, are complete mix digesters. Digester No. 1 constructed
in 1989, consists of a 50-foot diameter digester tank, a dual-fuel sludge heat exchanger, a 300 GPM
sludge recirculation pump, a complete mix digester gas system, gas collection, condensate recovery and
conditioning system, gas volume and usage metering, and sludge level and floating cover level metering.
Digester No. 2, built in 1963 and improved in 1996, consists of a 50-foot diameter digester tank, a dualfuel sludge heat exchanger, sludge recirculation pump, a complete mix digester gas system, gas collection
and condensate recovery system, gas volume metering, and sludge level metering. Total primary digester
volume is 808,370 gallons.
Digester No. 3, built in 1939, was improved in 1996 and is currently used as a secondary digester. The
digester is a 35-foot diameter tank with a fixed cover. There is no heating or mixing system associated
with Digester No. 3. The total secondary digester volume is 244,222 gallons.
The “old” out of service digester, also built in 1939, was cleaned and the covered removed in 1996. It is
currently being used as a digested sludge storage tank.
Thickened primary and waste activated sludge can be fed to either of the two primary digesters. Digester
gas is collected in the three digesters and stored in Digester No. 1, under the floating cover. The floating
cover has approximately 20,000 cubic feet of storage volume. The gas can be used for fuel for the
engine-generator (G-1), Digester No. 1 and No. 2 dual-fuel sludge heat exchangers, or flared using the
waste gas burner.
The organic treatment capability of the digestion system, based on the total primary digester volume of
108,070 CF, would be approximately 8,646 lbs. VTSS per day.
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Harding ESE, Inc.
6.5.7.2
The condition of the anaerobic digestion components is summarized in Table 6.5.5. A more complete
description is included in the following paragraphs.
Item Description
Digester No. 1
Dual-fuel sludge heat
exchanger
Recirculation pump
Complete mix system
Gas collection system
Building
Digester No. 2
Dual-fuel sludge heat
exchanger
Recirculation pump
Complete mix system
Gas collection system
Building
Table 6.5.5
Anaerobic Digestion
Condition Summary
Condition
Useful Life
Remaining (years)
Good
15
Poor
Poor
Fair
Good
<1
<1
10
25
Good
20
Good
Good
Good
Good
10
15
15
25
Comments
Tubes require periodic
replacement
Motor out, seals leaking
Compressor out of service
Piping replacement < 5 years
Exterior re-seal; interior repaint
Installed in 1996
Installed in 1996
Installed in 1996
Installed in 1996
Anaerobic Digester No. 1
Digester No. 1, shown in Figure 6.15 was constructed in 1989 and is generally in good condition. The
various components that comprise the complete mix digester system are in poor to good condition.
The dual fuel sludge heater boiler tubes have
been replaced several times since installation.
The digester gas is corrosive and has decreased
the life of the tubes. United Water contracts out
the maintenance and repairs to the sludge heater
and heat exchanger and it is maintained in good
condition. The anticipated remaining useful life
of the heat exchanger is approximately 15 years,
but system components will require replacement
prior to that time.
Figure 6.15 - Digester No. 1
A 5 HP, 300 GPM centrifugal pump re-circulates the sludge in the digester tank and through the sludge
heater. The electric motor had failed and was being replaced during the site visit. On a prior visit, it was
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Harding ESE, Inc.
noted that significant seal water and/or sludge was leaking from the pump seal. Due to the importance of
the pump, a stand-by unit should be considered.
The complete mix system is comprised of a belt drive gas compressor, gas piping, gas safety equipment,
and three gas guns. During the site visit, the gas compressor was out of service due to a failed impeller.
The piping that was accessible for inspection appeared to be in fair to poor condition on the interior, with
a majority of the piping exterior painting in good condition. The piping will need to be completely
replaced in the next five years (small sections of piping have already been replaced). The piping inside of
the digester tank was coated on the inside of the pipe with an epoxy paint system prior to the initial
installation. So, this piping is most likely in better condition than the piping in the digester gas room, but
it would be prudent to replace the gas piping in the digester tank in five years also. Replacement of the
piping will require the digester be taken out of service, drained and access made through the manways in
the floating cover. The digester tank should be cleaned and inspected at that time. The system will have
been in service for approximately 15 – 16 years in five years and other repairs may be required to the
digester tank, floating cover or the mixing gun system.
The gas collection system consists of the floating cover, piping, and gas safety devices. The collection
piping is primarily ductile iron pipe and appears to be in good condition. This entire system should be
inspected when the digester is taken out of service in five years for gas mix system piping replacement.
The waste gas burner, roof mounted on the south side of the building, should be inspected by a qualified
technician and repairs made as required. The burner appears to be in fair condition, but the gas control
panel enclosure is in poor condition. The pilot burner, fueled with natural gas, runs continuously. The
original design for the system provided for ignition of the pilot burner only during periods of high
digester gas pressure above a certain set point.
The digester building is in good general condition, but there are some maintenance and repairs that need
to be completed. Appendix C contains the list of items related to the building identified by the City and
United Water that need to be completed in the near future.
Anaerobic Digester No. 2
Digester No. 2, shown in Figure 6.16, was upgraded
in 1996 and is in good general condition. All of the
major system components were replaced in 1996,
including the sludge heat exchanger, re-circulation
pump, complete mix system, gas collection system,
building heating and ventilation, and a majority of
the sludge piping. These components are in good
condition. The sludge piping that was not replaced
is in fair condition, and needs to be repainted.
Figure 6.16 - Digester No. 2
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Harding ESE, Inc.
The Digester No. 2 tank was rehabilitated on the exterior in 1996. The original bricks, installed in 1963,
were removed, the tank height was increased by placing concrete walls on the top of the old tank, and
split face CMU’s were installed around the exterior of the tank. The CMUs need to be resealed with a
waterproof coating. The digester building, constructed in 1963, has the original brick exterior and
appears to be in good condition.
6.5.8
6.5.8.1
Metering/Instrumentation/Controls
General Description
Nearly all of the facility meters, instruments and control systems were replaced or upgraded during the
1989 plant improvements project, or more recently in some cases. Exceptions to this are the influent
meters, which were installed previous to the 1989 improvement project. The facility contains seven
Allen-Bradley PLCs, four significant HVAC control panels, two major motor control centers and
numerous power panels.
The PLCs are linked to a central computer system located in the Control Building, second floor office
area. Alarm system status and system controls are available from the central computer utilizing RSView
Software. Alarms are telemetered by an Advotech system to an emergency telephone number during off
hours. Table 6.5.6 includes a listing of the meters and PLCs, their location, function, and estimated years
of service.
6.5.8.2
The following paragraphs are condition reports for various control panels throughout STP #1.
Ventilation Control (Belt Thickener & Heat Exchanger Area)
Overall, this panel is in relatively good condition but does show signs of hydrogen sulfide corrosion.
All bare copper and brass fuses are black with corrosion.
Wiring internal to the panel is coated copper wire and shows no signs of corrosion. Wiring brought
into the panel is stranded copper and shows significant signs of corrosion and should be replaced.
To prevent the migration of hydrogen sulfide gases, sealoffs should be installed on all conduits
coming from or going to this panel.
It is also recommended that Hoffman Corrosion inhibitors be maintained within the panel. Internal
wiring is wire tagged with permanent plastic markers. External wiring (wire entering the control
panel from a conduit) currently has paper wire tags that have started to deteriorate and fall off. It is
recommended that these paper wire tags be replaced with plastic tags like those on wiring internal to
the panel.
Currently, front panel mounted switches, fuse blocks and other internal panel devices are
inconsistently labeled. It is recommended that all internal panel devices be permanently labeled and
that the panel be permanently labeled internally. It is recommended that a documentation rack be
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Harding ESE, Inc.
installed in the panel and that the copy of the associated documentation be maintained within the
panel.
Remove debris and clean out the bottom of the cabinet
Table 6.5.6
Meters and Programmable Logic Controllers
Item
CP-PC-PLC
CP-PS-PLC
Location
Control Building
Digester No. 1 Bldg.
Service
Primary Pumps and Sludge Pumping
Engine/Generator
CP-BL-PLC
CP-TH-PLC
CP-FP-PLC
CP-HG-PLC
CP-BM-PLC
Drying Bed Bldg.
Blower Building
Blower Building
Influent Flow Meter
Influent Flow Meter
Effluent Flow Meter
Effluent Flow Meter
Effluent Flow Meter
D.O. Meter
D.O. Meter
D.O. Meter
Turbidity Meter
Turbidity Meter
Turbidity Meter
Chlorine Residual
Chlorine Residual
Chlorine Residual
Sludge Meter
Sludge Meter
Electric Meter
Electric Meter
Gas Meter
Control Building
Control Building
Control Building
Control Building
Control Building
Blower Building
Blower Building
Blower Building
Blower Building
Blower Building
Blower Building
Blower Building
Blower Building
Blower Building
Drying Bed Building
Gas Meter
Digester No. 1 & No. 2 Heat
Exchanger
Sludge Drying Bed System
Diversion Chamber Hydraulic Gates
Blower System, DO, FBOP Sludge
Pumping
East Effluent
West Effluent
North Secondary Effluent
South Secondary Effluent
FBOP Effluent (East Secondary)
North Secondary
South Secondary
FBOP Secondary (East Secondary)
WAS & Primary Sludge
Digested Sludge
CILCO KWH
G-1 KWH
Digester No. 1 Digester Gas
Production
Digester No. 2 Digester Gas
Production
Years of
Service
11
11
11
11
11
12
11
18
18
10
10
5
11
11
5
5
5
5
8
8
5
11
11
11
11
11
11
Primary Effluent Pump Control Panel (CP-PC)
The following upgrades are recommended for this control panel.
Permanently label all relays, switches, panel meters and internal devices.
Label processor with associated rack, rung and slot designations.
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Harding ESE, Inc.
Provide documentation rack and associated panel documentation.
Replace paper wire tags with permanent plastic tags.
Reroute wiring within the panel through the provided raceway and reinstall the raceway covers.
Provide permanent internal and external panel identification tag. (CP-PC)
Permanently label all internal panel devices (i.e. power supplies, signal conditioners, etc.)
All terminations should be retorqued.
Label all spare wiring as to origination/destination etc.
Remove debris and clean out bottom of control panel.
Primary Sludge Pumping System Control Panel (CP-SP)
Overall this panel is in good condition. The following modifications are recommended.
Label switches, panel meters, transformer and relays permanently.
Label the processor and associated rack rung and slot designations.
Provide permanent internal and external panel identification tag. (CP-SP)
Remove debris and clean out bottom of control cabinet.
Ventilation Control Panel-(Generator Room, Generator #1 & Generator #2)
This panel has corrosion consistent with exposure to hydrogen sulfide gas. The following improvements
are recommended:
terminated in the control panel.
Provide permanent internal panel identification tag.
Label all internal devices, fuses, switches, transformers, relays etc. with permanent labels.
Hoffman Vapor Corrosion Inhibitors are recommended to be installed and maintained.
Significant corrosion is apparent on all bare copper wires and brass fuse ends. It is recommended that
all external wiring be re-terminated or replaced to eliminate all corrosion.
Replace paper based wire tags with permanent plastic tags.
Remove debris and clean bottom of the cabinet.
Boiler System Control Panel (CP-BL)
Overall, this panel is showing signs of deterioration caused by hydrogen sulfide gas. The following
upgrades are recommended:
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Harding ESE, Inc.
Remove debris and clean the cabinet
Label processor with associated rack, rung and slot designations.
Significant corrosion is apparent on all bare copper wire and brass fuse ends. It is recommended that
all external wiring be re-terminated or replaced to eliminate apparent corrosion and that fuses be
replaced. Internal panel wiring appears okay.
Alarm buzzer needs to be re-terminated.
Hoffman Vapor Corrosion Inhibitors are recommended to be reinstalled and maintained.
In order to prevent the migration of hydrogen sulfide gases, sealoffs should be installed on all
conduits terminated in the control panel.
Provide permanent internal panel identification tag. (CP-BL)
Label all internal devices, power supplies, fuse blocks, switches, breakers, panel meters, etc. with
permanent labels.
Replace paper wire tags with permanent plastic tags.
Replace door seal
Remove all jumper wires
Establish procedure for maintaining up-to-date panel documentation.
Auxiliary Boiler Control Panel (CP-BL Aux.)
Hydrogen sulfide gas corrosion is already apparent within this panel. The following improvements are
recommended:
Permanently label all starters associated with the auxiliary boiler system currently residing in the
boiler room.
Provide permanent internal and external panel identification tags. (CP-Aux. BL).
Corrosion is apparent on all bare copper wire. It is recommended that all corroded wiring be reterminated or replaced as required to eliminate all corrosion.
Permanently label all internal panel devices (i.e. switches, panel meters, etc.).
Provide documentation associated with panel and documentation rack/holder.
Provide permanent wire tags for all internal wiring.
Gas Compressor Control Panel (CP-GC)
This panel is showing signs of deterioration consistent with hydrogen sulfide gas exposure. The
following improvements are recommended:
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Harding ESE, Inc.
Provide permanent internal and external panel identification tag. (CP-GC)
all external wiring be re-terminated or replaced to eliminate all corrosion and that fuses that are badly
corroded be replaced.
Replace paper wire tags with permanent plastic tags similar to existing internal wire tags.
Label processor with associated rack, rung and slot designations as required.
Replace door seal.
Remove debris and clean out bottom of the cabinet.
Generator Control Panel (CP-PS)
This panel is showing signs of deterioration associated with hydrogen sulfide gas exposure. The
following improvements are recommended for this panel:
Provide permanent internal and external panel identification tag. (CP-PS)
Waste heat system cooling water temperature panel meter is currently not working. Fix as required.
Permanently label all internal panel devices such as switches, panel meters, relays, breakers, fuse
boxes, etc.
Remove debris and clean out bottom of the control cabinet.
Boiler Control Panel (Mounted on Aux. Boiler)
Label all internal devices permanently.
Label all internal wiring permanently.
Provide disconnecting means for power to control panel.
Provide accurate wiring documentation and store in documentation rack/holder.
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Harding ESE, Inc.
Gravity Belt Thickener (CP-TH)
This panel is showing signs of deterioration associated with hydrogen sulfide gas exposure. The
following improvements are recommended:
Provide permanent internal and external panel identification tag. (CP-.TH)
Replace all corroded wiring associated with this panel.
Permanently label all internal panel devices such as switches, panel meters, relays, breakers, fuse
boxes, etc.
Retorque all internal connections.
Clean interior of control panel.
Label all unused wires as to origin/destination.
Establish procedure for maintaining accurate and up-to-date panel documentation.
Blower Control (CP-BM)
Overall, this panel is in relatively good condition and doesn’t exhibit corrosion similar to other panels.
The following improvements are recommended:
Label incoming wiring permanently.
Label power supply control relays, switches, breakers, etc. permanently.
Label processor with rack, rung, and slot designations.
Label all unused wires as to origin/destination.
Permanently label interior and exterior of control panel (CP-BM).
Provide documentation and associated documentation rack.
6.6
Sewage Treatment Plant No. 2 (STP#2)
STP#2, shown in Figure 6.17, is presently being used for wastewater storage during wet weather
conditions when the CSOs are overflowing. The existing plant, built in 1971 and expanded in 1975,
includes two activated sludge treatment units (north unit is shown in Figure 6.18), polishing pond, blower
and office building, and sludge drying beds. The plant was removed from service in 1989, following
completion of the north side interceptor sewer. The decision to discontinue the use of the 1MGD plant
was based on the estimated cost to rehabilitate and operate the plant compare to the construction of a new
interceptor sewer. It was determined that the annualized costs of improving, operating and maintaining
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Harding ESE, Inc.
Figure 6.17 - STP No. 2
STP #2 would be in excess of the cost of constructing an interceptor sewer and transporting the
wastewater to STP#1 for full treatment.
The condition of STP#2 is fair to poor. The components were all inspected and while some could be
salvaged, many will require replacement if the treatment plant was returned to service. When in
operation, the treatment systems were difficult to operate and compliance with the discharge permit was
inconsistent. The design of the original system was less than ideal and restoring the existing plant is
discouraged.
The north and south treatment unit structures are in
fair condition, but the air piping, diffusers, clarifier
system, sludge pumps, weirs and baffles, and scum
box are in poor condition. The bar screen is in good
condition, but the comminutor appears to be
inoperable. The flow meters are inoperable and the
control gates have been removed. The polishing
pond as determined by a previous pond study, has
apparent leaks in the pond floor and the chlorination
system is inoperable.
43
Figure 6.18 - STP No. 2 - North Unit
Harding ESE, Inc.
6.7
6.7.1
CSO Settling and Chlorine Contact Basin – STP #1
General Description
The CSO Settling and Chlorine Contact Basins are used to store excess flow from the incoming combined
sewer system during wet weather conditions. If the flow exceeds the storage capacity of the CSO settling
basin, the flow passes into the chlorine contact basin and ultimately out to the Illinois River. The
combined storm water and wastewater retained in the basin after a storm event is pumped back into the
interceptor sewer to STP #1 for full treatment.
Both basins have concrete walls and floors that were upgraded in the early 1990s.
6.7.2
The basins are generally in good condition. United Water staff have indicated that they have had
problems with the pumping system due to solids collecting in the sump. Operational experience has
proven there is a tendency for significant volumes of solids to collect in the CSO settling basin and to
some extent in the chlorine contact basin. Typically the plant operators clean the settling basin with a
tractor loader. This is only somewhat successful due to the high water content of the solids. The chlorine
contact basin must be cleaned manually by hand. These methods of cleaning have been time consuming
and difficult, and cleaning of the basins is the primary issue to be resolved with this system.
Improvement options evaluation is included in Section 7.4.
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Harding ESE, Inc.
7.0 Wastewater System Improvement Options
7.1
7.1.1
Combined Sewer Overflow Structures
Problems associated with the Fayette Street regulator structure, flap gate, and outfall are two-fold. First,
the manway to the regulator is in Fayette Street and difficult to access, resulting in the second issue which
is maintenance. The slide gates require exercising and lubrication, at least annually. The flap gate needs
to be inspected on a regular basis, preferably following each overflow occurrence.
The proposed improvement to the Fayette Street CSO includes replacement of the slide gates with
stainless steel units. The estimated cost to replace the 15- and 18-inch slide gates is shown in Table 7.1.1.
Table 7.1.1
Cost of Improvements
Item
Replace 15-inch slide gate with stainless steel unit
Replace 18-inch slide gate with stainless steel units
Structure sealing
Subtotal
Contingency
Engineering & Administration
Estimated Total
7.1.2
Estimated Cost
$ 7,500
$ 8,500
$ 1,500
$17,500
$ 1,750
$ 2,900
$22,150
The recommended improvements at Court Street CSO include repair of the concrete structure, site
improvements to reduce required maintenance including vegetation removal and installation of a
bituminous surface from the structure to outside the fenced area, sealing of pipe penetrations, and
replacement of the slide gates. The estimated cost of the improvements is listed in Table 7.1.2.
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Harding ESE, Inc.
Table 7.1.2
Item
Repair concrete structure
Site improvements
Seal pipe penetrations
Replace 15” sluice gate
Subtotal
Contingency
Estimated Total
7.1.3
Estimated Cost
$ 5,000
$ 2,500
$ 1,500
$ 7,500
$18,000
$34,500
$ 3,450
$ 5,700
$43,650
The Model 30” TF-2 Tideflex Check Valve was reinstalled in the mid-1990s after becoming loose from
the discharge pipe and allowing river water to enter the combined sewer system. The valve appears to be
in good condition but requires periodic inspection to clean any debris that may be lodged in the valve.
The 12-inch sluice gate and the 21-inch slide gate are inoperable and need to be replaced with similarly
constructed units or stainless steel units, since the stainless steel units will perform better when minimal
maintenance is performed on the gates. The estimated cost of improvements is listed in Table 7.1.3.
Table 7.1.3
Item
Replace 21” slide gate
Subtotal
Contingency
Estimated Total
7.1.4
Estimated Cost
$ 6,000
$10,000
$ 1,600
$ 3,450
$ 2,600
$36,200
State Street Outfall
The State Street Outfall requires periodic maintenance which includes inspection and cleaning of the 60inch and 72” x 48” flap gates. The structure is in fair condition.
7.2
The following options have been identified to resolve the solids accumulation problem in the State Street
Basin.
46
Harding ESE, Inc.
Aeration System
Under this option, an aeration system will be installed on the floor of the tank with adequate air supplied
to keep the solids in suspension. This would require a system of diffusers mounted to the floor as well as
a blower system to supply the necessary air. This system will not be pursued due to the high cost of a
blower system and associated building, the noise problems associated with blowers in a residential area,
and the difficulty of maintaining diffusers when only used on an intermittent basis.
Flushing System with Domestic Water
A series of high-pressure nozzles will be installed throughout the tank to flush the solids into the drain
channel and back into the wet well where the waste will be pumped into the sewer system. This approach
will require a separate wet well for water storage and a high-pressure pump to supply the nozzle system.
The wet well will be filled from the City water main. This approach will require a water meter, a
backflow preventer, and pressure relief valve to protect the pump. Water will be purchased from IllinoisAmerican Water Company. This alternative will not be pursued due to the need for a high-pressure
pump, the need for an additional underground structure to store the flushing water, and the added cost of
purchasing water.
Flushing System with Wastewater
This concept shown in Figure 7.2.1 will use one of the existing sewage pumps to supply wash water to the
basin for flushing purposes. Electric valves in the pump house will control diversion of water to the
basin. Under normal conditions when the basin is not being cleaned, the pump will be used in rotation
with the other pumps to pump wastewater to the interceptor sewer. An inline grinder will be required in
the main flushing line to prevent large solids from plugging the discharge ports on the flushing headers.
With this approach a large volume of water (approximately 600 to 700 gpm) will be concentrated on a
small area of the tank to move the solids to the drain channel and ultimately into the wet well. To
accomplish this, the tank will be flushed in sequence via electric control valves. The timing of the valve
sequence will be controlled by the PLC used for the pump system. If the solids buildup in the tank is
heavy, it may be necessary to cycle through the flushing sequence two or three times. The electric valves
for sequencing the headers will be located outside the tank in a separate building. The building will serve
two purposes; 1) to facilitate maintenance of the valves, and 2) to allow the valves to be installed above
the flood level of the Illinois River. The valves could be mounted in the tank, however, this would
require explosion proof operators and maintenance would be extremely difficult due to limited access and
the potentially harmful environment in the tank. The estimated cost for installation of this system is
approximately $141,000. A cost breakdown is shown in Table 7.2.1.
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Harding ESE, Inc.
6” HEADER W/DISCHARGE PORTS
FOR FLUSHING (TYPICAL)
8”
ELECTRIC
PLUG VALVES
6” HEADER W/DISCHARGE PORTS
FOR FLUSHING (TYPICAL)
8”INLINE
GRINDER
8”BURIED MAIN
BUILDING TO
HOUSE VALVES
6” ELECTRIC PLUG
VALVES (TYP)
Figure 7.2.1 - State Street Basin Cleaning Concept
Table 7.2.1
State Street Basin
Cost of Flushing Improvements
No.
1
2
3
4
5
6
7
8
9
10
Item
8” buried force main
8” electric plug valves in
pump house
6” electric plug valve
Core drill walls for pipes
Interior piping
Building to house valves
Conduit & wiring
PLC programming
Grinder for flushing water
Seeding
Quantity
100
2
LF
EA
10
10
840
250
1
1
1
1
EA
EA
LF
SF
LS
EA
EA
LS
48
Units
Unit Price
$
50.00
$ 2,500.00
Total Price
$ 5,000.00
$ 5,000.00
$ 4,500.00
$ 100.00
$
30.00
$
40.00
$ 3,500.00
$ 2,000.00
$14,000.00
$ 500.00
Subtotal
Contingency
Estimated Total
$ 45,000.00
$ 1,000.00
$ 25,200.00
$ 10,000.00
$ 3,500.00
$ 2,000.00
$ 14,000.00
$
500.00
$111,200.00
$ 11,120.00
$ 18,348.00
$140,668.00
Harding ESE, Inc.
7.3
FCI Bar Screen
Proposed improvements at the bar screen facility include the following items:
•
Rehab exterior lights
•
Clean and repaint all exterior and interior metal surfaces
•
Replace overhead door and install electric opener
•
Re-insulate ceiling and cover wood components
•
Seal exterior masonry walls
•
Seal all wall penetrations from the bar screen room
•
Install new HVAC systems
The estimated cost for the proposed improvements is listed in Table 7.3.1.
Table 7.3.1
FCI Bar Screen
Item
Electrical/Mechanical Improvements,
including lighting, HVAC, and door opener
Overhead door replacement
Painting, sealing, and insulation
Subtotal
Contingency
Estimated Total
7.4
Estimated Cost
$7,500
$3,000
$4,500
$15,000
$1,500
$2,500
$19,000
CSO Settling and Chlorination Basin – STP #1
The following two options have been evaluated for solids removal from the CSO Settling and
Chlorination Basins.
Option 1
Option 1 consists of the installation of a pumping station on the existing fill line, a buried main on the
south and east sides of the basins, and a header system with electric valves and flushing ports in each
basin. In both Option 1 and Option 2 it is still recommended that a loader tractor be used to remove the
majority of solids from the settling basin. Flushing heavy loads of solids back into the sewer system
could cause buildups in the sewer system, plugging of the discharge pump, and excessive loadings for the
process treatment facilities. The flushing system will be used to clean the settling basin once the heavy
solids have been removed. Since tractor access is not available in the chlorine contact basin, the flushing
system will be used to flush the solids into the line that drains back into the settling basin. The floor of
the chlorine contact basin must be sloped toward the north to facilitate proper draining, which could be
49
Harding ESE, Inc.
accomplished by adding a few inches of concrete to the floor. Two small holes will be required in the
baffle walls to allow the floor to drain toward the drain line. The pump station will be capable of
pumping about 1000 gpm. To flush the floors of the basins it is anticipated that a large volume of water
will be required on a relatively small area. This will require electric valves, in conjunction with a PLC
controller, be used to sequence the flushing process. Three fire hydrants will also be included on the
perimeter of the basins for supplemental hose flushing, if required. The electric valves may have to be
elevated above the top of slope elevation to prevent damage during flooding conditions along the Illinois
River. The estimated cost of this option is approximately $218,000. A cost breakdown is shown in Table
7.4.1.
Option 2
Option 2, as shown in Figure 7.4.1, consists of the installation of a pumping station on the existing fill
line, a buried main on the south and east sides of the basins, drop legs on the slope of the chlorine contact
basin for connection of a portable hose flushing unit, access ramp to the chlorination basin, revisions of
baffle walls, and drop legs on the slope of the settling basin for connection of portable hose flushing unit.
As mentioned under Option 1, it is recommended that a loader tractor still be used to remove the majority
of solids from the settling basin. Once the heavy solids have been removed from the settling basin, a
portable hose unit can be connected to the drop legs for manual clean up of the remaining solids. These
solids will be flushed into the existing sump pit and pumped into the sewer for processing at the plant.
Figure 7.4.1 - Storm Basin - Option No. 2 Improvements
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Harding ESE, Inc.
Tractor access will be made to the chlorine contact basin through the addition of a concrete access ramp.
The existing concrete baffles will be modified to allow space for a small skid loader to move around the
baffle ends. The flushing system will be used to flush the remaining solids into the line that drains back
into the settling basin. The floor of the chlorine contact basin must be sloped toward the north to facilitate
proper draining. This could be accomplished by adding a few inches of concrete to the floor. Two small
holes will be required in the baffle walls to allow the floor to drain toward the drain line. Similar to the
settling basin, drop legs will be installed in the chlorine contact basin for hose connection for final
cleanup. The pump station will be capable of pumping about 1000 gpm. Electric valves will not be
required with this option. Perimeter hydrants will also be available for additional hose cleanup, if
necessary. The estimated cost of this option is approximately $175,000. A cost breakdown is shown in
Table 7.4.2.
Table 7.4.1
Option 1
Wastewater Plant Basin
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Item
6” main at top of slope
6” drop legs on slopes
4” header pipes
6” electric valves
Fire Hydrants
Nozzles
Concrete for slope in
chlorination chamber
Pump Station
Concrete slab repair
Holes in chlorine baffles
Electrical feed for pump station
Seeding
PLC Controller
Quantity
225
340
305
300
11
3
80
1
Units
LF
LF
LF
LF
EA
EA
EA
LS
1
100
2
1
1
1
EA
SF
EA
LS
LS
LS
51
Unit Price
$
50.00
$
50.00
$
50.00
$
30.00
$ 3,000.00
$ 2,000.00
$
50.00
$ 2,500.00
Total Price
$ 11,250.00
$ 17,000.00
$ 15,250.00
$ 9,000.00
$ 33,000.00
$ 6,000.00
$ 4,000.00
$ 2,500.00
$ 63,000.00
$
5.00
$
500.00
$ 5,000.00
$ 1,000.00
$ 4,000.00
Subtotal
Contingency
Estimated Total
$ 63,000.00
$
500.00
$ 1,000.00
$ 5,000.00
$ 1,000.00
$ 4,000.00
$172,500.00
$ 17,250.00
$ 28,463.00
$218,213.00
Harding ESE, Inc.
Table 7.4.2
Option 2
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
7.5
7.5.1
Item
3” header pipes in cl basin
3” plug valves
Fire Hydrants
Nozzles
Pump Station
Seeding
Hose reel & cart
Access ramp to chlorination
chamber
Baffle wall revisions
Quantity
50
250
75
235
3
4
30
1
Units
LF
LF
LF
LF
EA
EA
EA
LS
Unit Price
$
50.00
$
40.00
$
30.00
$
30.00
$ 3,000.00
$ 2,000.00
$
50.00
$ 2,500.00
Total Price
$ 2,500.00
$ 10,000.00
$ 2,250.00
$ 7,050.00
$ 9,000.00
$ 8,000.00
$ 1,500.00
$ 2,500.00
1
25
2
1
1
1
1
EA
SF
EA
LS
LS
EA
LS
$ 63,000.00
$
5.00
$
500.00
$ 5,000.00
$ 1,000.00
$ 2,000.00
$17,500.00
$ 63,000.00
$
125.00
$ 1,000.00
$ 5,000.00
$ 1,000.00
$ 2,000.00
$17,500.00
4
EA
$1,500.00
Subtotal
Contingency
Estimated Total
$6,000.00
$138,425.00
$ 13,842.50
$ 22,850.00
$175,117.50
Wastewater Treatment-STP #1
STP #1 Replacement-General
For comparison purposes, several different processes have been evaluated to provide primary and
secondary treatment in addition to the conventional activated sludge process. At the request of the City
and United Water, two processes were evaluated that do not require the primary treatment process.
The systems evaluated for the upgrade and expansion of STP #1 include:
1.
2.
3.
4.
5.
Conventional activated sludge;
Counter Current aeration (Schreiber) without primary treatment;
Counter Current aeration (Schreiber) with primary treatment;
Sequence batch reactor (Aqua-Aerobics); and
Vertical loop reactor (Envirex) with primary treatment.
For construction cost comparisons, the unit costs listed in Table 7.5.1 were utilized as common to all
systems.
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Harding ESE, Inc.
Table 7.5.1
Construction Unit Costs
Item
Concrete - Slab on grade
Concrete - Curved wall
Concrete - Straight wall
Concrete - Spiral formed
Construction Cost
$300/yd3
$450/yd3
$400/yd3
$650/yd3
$7.00/yd3
Excavation:
The proposed facilities are all designed to treat a DAF of 6.84 MGD with a peak hourly flow of 15.39
MGD. Design loading will be 11,219 lbs/day BOD5, 15,910 lbs/day TSS and an ammonia concentration
of 25 mg/l. Design effluent is 20 mg/l BOD5 and 25 mg/l TSS.
In addition to the evaluation of the major treatment systems, the study includes an evaluation of other
treatment components including:
•
Primary clarifiers;
•
Secondary clarifiers;
•
Expansion of the chlorination facilities for disinfection or replace them with UV disinfection; and
•
Re-use and expansion of the existing sludge thickening, dewatering and lagoon system or replace
portions of the system.
The evaluation of options for these systems are included in the following paragraphs. Recommendations
made for these treatment systems are included in the overall treatment plant capacity expansion options
and final upgrade recommendation.
7.5.1.1
Primary Clarifiers
Two options were considered to improve and expand the capacity of the primary treatment system. The
first option includes improving the existing four primary clarifiers and adding one additional clarifier.
The second option considers replacement of all of the existing clarifiers with two new clarifiers.
Option No. 1
The four existing primary clarifiers will require significant refurbishing to extend their useful life through
the next 20 years. The required improvements include:
•
Significant concrete removal and repair on all of the concrete structures;
•
Clarifier mechanism replacement in all four clarifiers;
•
Handrail, sidewalk, and site improvements around all four structures;
•
Sludge piping and valve replacement; and
53
Harding ESE, Inc.
•
Split flow chamber improvements.
In addition to these improvements, a new 65-foot diameter primary clarifier will need to be constructed in
a portion of the existing sludge lagoon. The estimated cost to refurbish all four clarifiers as described
above and install the new clarifier is $1,035,200.
Option No. 2
Two 85-foot diameter clarifiers (see Appendix E for clarifier details) will be required to provide adequate
clarifier surface area for the 20-year planning period, a surface settling rate of 1,200 gallons-per-day per
square foot, and a 30 percent BOD5 removal. The estimated cost of two new clarifiers, sludge piping and
valves, aluminum handrail system, sidewalks, site improvements, and primary pump improvements is
$990,000.
The selected primary clarifier option is No. 2, based on a lower construction cost and anticipated lower O
& M costs for the two new 85-foot diameter clarifiers.
7.5.1.2
Secondary Clarifiers
The following two options were considered for improving and expanding the secondary clarifier system
(see Appendix F for clarifier details).
•
Option No. 1 – Refurbish the existing clarifiers and construct an additional clarifier to add the
required capacity to meet the 20-year projected loading.
•
Option No. 2 – Construct new secondary clarifiers to replace the existing clarifiers and to meet the
projected wastewater loading.
Option No. 1
The north and south clarifier mechanism and structures are not in adequate condition, without significant
refurbishing, to have a 20-year useful life. Based on the initial tank design as a “package” treatment
system, utilizing the clarifier without continuing the use of the treatment compartments surrounding the
clarifier would require structural enhancement to the clarifier walls. This is a significant factor due to the
fact that abandonment of the other treatment compartments is inevitable as the plant capacity is expanded.
Due to the structural limitations of the tanks, the condition of the mechanism, and the requirement to
construct a fourth clarifier (space requirements are limited at STP #1), this option has not been
considered further.
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Harding ESE, Inc.
Option No. 2
This option includes the replacement of the secondary clarifiers with two 130-foot diameter clarifiers.
The existing clarifier No. 3 would remain and could be used as additional clarifier capacity during periods
of high flow. The new clarifiers are sized for a peak flow rate of 15.39 MGD with a surface settling rate
(SSR) of 800 gallons/day/square foot, a solids loading rate of 50 pounds/day/square foot, and a weir
loading rate of 30,000 gallon/day/lineal foot.
The following improvements are included in this option, in addition to the two 130-foot diameter
clarifiers.
•
Scum pump station and forcemain
•
WAS/RAS pump station and piping
•
Influent and effluent piping
•
Site and road improvements
The estimated construction cost of Option No. 2 is $1,000,000.
7.5.1.3
Disinfection System
An evaluation of disinfection system options was performed for STP #1. The options considered include:
•
Expansion of the existing chlorination system; and
•
UV disinfection.
Several factors were considered in the evaluation, including:
•
Safety;
•
Construction cost;
•
O & M cost; and
•
Compatibility with the treatment system and final plant effluent.
Currently, the plant personnel maintain a minimum number of 150-pound chlorine cylinders to prevent
exceeding the OSHA threshold that requires a risk management plan. According to the plant personnel,
this is a difficult task and results in frequent chlorine cylinder deliveries, requiring additional plant
personnel time to assist with the cylinder delivery. Once the plant is expanded, this process would
become excessive and a risk management plan would be required. An inherent advantage to the UV
disinfection system is in the area of safety. Therefore, from a safety issue, the UV would be the system of
choice.
55
Harding ESE, Inc.
Construction costs for both options are listed in Table 7.5. While the concrete contact basin cost is higher
for the chlorination system, the UV equipment cost is quite high which results in a higher overall
construction cost for the UV system.
Table 7.5
Wastewater System Options Evaluation
Disinfection System
Alternatives
Capital Costs
Chlorination System
-Chlorine
-Labor
-Feeder Repairs
System Total – CL2
UV Disinfection System
-Power
-Labor
-Lamp Replacement
System Total – UV
Annual O & M
Costs
Present Worth
$325,800
$325,800
$530,000
$530,000
$34,300
$10,920
$ 1,000
$46,220
$855,900
$18,900
$ 1,560
$ 6,350
$26,810
$837,500
Based on current chlorine gas costs, provided by United Water, power usage, bulb life, and bulb costs,
provided by INFILCO for their Aquaray  40, the O & M costs are less for the UV system than they are
for the chlorination system. Calculating the present worth of both systems over 20 years at a six percent
discount rate, the UV system has the lower present worth of $837,500. (See Appendix G for additional
UV information).
Based on these considerations, the UV system is included in all of the treatment options for the proposed
disinfection system.
7.5.1.4
Sludge Thickening and Dewatering
There were multiple options considered for primary and waste activated sludge thickening, as well as
sludge dewatering. Sludge thickening options evaluated include:
•
Addition of a second gravity belt thickener;
•
Installation of a belt press to serve as a thickener and sludge dewatering unit; and
•
Installation of a centrifuge to serve as a thickener and a sludge dewatering unit.
Option No. 1
The existing Envirex GBT has performed very well for thickening both primary and waste activated
sludge. But since the GBT is operated nearly every day, a backup system is advisable. Installation of a
second GBT, slightly larger than the existing 2.5 meter thickener, has been evaluated. The new GBT
would serve as the main thickener, and the 2.5 meter thickener would serve as a backup unit. The
56
Harding ESE, Inc.
estimated cost to install a new 3.0 meter Envirex/JWI GBT in the existing Drying Bed Building,
including piping, polymer feed, pumps, controls and building revisions is $280,000.
Based on an analysis of sludge disposal costs, the present method of sludge disposal appears to be the
least expensive. The plant currently utilizes the sludge lagoons for digested sludge storage and contracts
for the sludge to be land applied at a cost of $0.034 per gallon, plus lime costs if required. Currently the
vacuum-assisted drying bed serves as a backup disposal system be in-place should problems develop with
the lagoon space or land availability.
Operating staff experience has not been good relative to the vacuum assisted drying bed system. The
labor costs are considerable for cleaning the beds, the drying results unpredictable and the polymer costs
also higher than anticipated. Based on these issues, replacement of this system as a backup to the sludge
lagoon and land application disposal process is advisable.
Under Option No. 1, installation of either a belt press or a centrifuge has been considered. The
dewatering equipment will be installed in the existing Drying Bed Building.
The estimated cost to construct the belt press system is $352,000. This cost includes:
•
One Model GRS-2 Series III Kompress-Komline Sanderson 2.2 meter, 120 GPM, 1,800 pounds of
dry solids/hour belt press, or equal;
•
One Stranco polymer feed system;
•
Sludge pump and piping revisions;
•
Building and drain piping modifications; and
•
Screw conveyor system for dried sludge handling.
The estimated cost to construct the centrifuge system is $357,000. This cost includes:
•
One Model CA405 Westfalia centrifuge;
•
One Stranco polymer feed system;
•
Sludge pump and piping revisions;
•
Building and drain piping modifications; and
•
Screw conveyor system for dried sludge handling.
O & M costs are comparable for either the belt press or the centrifuge, according to information provided
by the manufacturers of the equipment. Since the system costs are comparable, the selection of the
process should be determined through a joint effort of the City, United Water and the consulting engineer.
For cost comparisons of the treatment system options, the higher cost system will be used. (See
Appendix H for additional information on the filter press and centrifuge).
The estimated construction cost for Option No. 1 is $637,000.
57
Harding ESE, Inc.
Option No. 2
Since the thickening system and the dewatering system are being proposed as a backup to the existing
facility, one piece of equipment to serve both purposes merits consideration. Option No. 2 considers the
use of a belt press for this purpose. Komline Sanderson manufactures a filter press/thickener unit that can
be operated to thicken or dewater sludges. The estimated construction cost for this system, including the
equipment, is $580,000.
Option No. 3
A centrifuge can also serve both as a thickener and a dewatering unit. The centrifuge is considered in this
option. The Westfalia CA405, as proposed in Option No. 1, has the ability to both thicken and dewater.
A similar unit is currently operating at a wastewater facility at Freeport, Illinois. The estimated
construction cost for this system, including the equipment is $357,000.
Option No. 3 is the selected option for sludge thickening and dewatering. This option and its related costs
are included in the treatment system improvement options presented later in this report.
7.5.2
STP #1 Upgrade-Conventional Activated Sludge Process
An upgrade of STP #1 to meet the projected hydraulic, organic, and solids loading for the next 20 years
will require improvements to the existing processes, plus the addition of treatment capacity. Table 7.5.2
contains a list of the wastewater treatment systems at STP #1, each systems current treatment capacity,
the 20-year projected loading requirement, and the additional capacity needed to meet the projected
wastewater flow.
Based on the condition of several of the treatment plant systems and the additional treatment capacity
required, replacement of the following components is recommended.
•
Bar screen and channel grinder with two mechanical coarse bar screens
•
Primary clarifiers with two 85-foot diameter clarifiers
•
Activated sludge process with new aeration tanks, fine bubble diffusers, blowers, return and activated
sludge pumps, and appurtenances.
•
Secondary clarifiers with two 130-foot diameter clarifiers
•
Chlorine disinfection system with a ultraviolet (UV) light system
•
Sludge vacuum assisted drying bed system with a centrifuge or gravity belt press, for backup to the
existing sludge lagoons
Improvements to the remaining systems will be required to meet the 20-year projected wastewater flows.
58
Harding ESE, Inc.
Table 7.5.2
STP #1 - Existing
Wastewater Treatment Capacity
Description
Planning Projection
Pre-Treatment
Primary Settling
Activated Sludge
Process
Secondary Settling
Anaerobic Digestion
Design Average
6.84 MGD
5.7 MGD
N.A.
4.99 MGD
Additional
Capacity
Required
N.A.
.14 MGD
N.A.
1.85 MGD
Theoretical
Peak Hourly
15.39 MGD
12.00 MGD
9.50 MGD
9.70 MGD
Additional
Capacity
Required
N.A.
3.39 MGD
5.89 MGD
5.69 MGD
N.A.
7.5 MGD
N.A.
(0.7 MGD)
14.86 MGD
N.A.
0.53 MGD
N.A.
These improvements will include:
•
Addition of a second grit removal system;
•
Upgrade of the primary effluent pumping system;
•
Addition of a second WAS pump;
•
Installation of an additional 150 KW dual-gas engine generator; and
•
Construction of an effluent pumping station.
The estimated cost of upgrading STP #1 is listed in Table 7.5.3. A conceptual layout of the improved and
expanded plant is shown in Figure 7.5.1. The cost estimate of the system improvement is based on the
following components:
•
Schreiber front load duplex screen system, or equal, to be located in the existing modified influent
channels that presently contain the bar screen and channel grinder, providing a DAF of 6.84 MGD
and a peak hourly flow of 15.39 MGD.
•
Duplicate grit system as existing and upgrade to existing aerated grit removal system, providing a
potential DAF of 11.4 MGD and a peak hourly flow of 24.0 MGD. The grit washer installed in 1999
will be reused.
•
Replacement of all four primary clarifiers with two 85-foot diameter WESTECH, or equal, primary
clarifiers, providing a total surface area of 11,325 square feet. A surface settling rate (SSR) of 1,200
gallon/day/square foot of tank area and 30 percent BOD removal is expected through the primary
clarifier system at a peak hourly rate of 15.39 MGD. System replacement includes:
- Concrete structures, including aluminum handrails;
- Clarifier mechanisms;
- Split flow chamber;
- Wastewater and sludge piping, valves and fittings;
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Harding ESE, Inc.
- Flow meters;
- Sludge and primary effluent pumping improvements;
- Sidewalks;
- Site improvements; and
- Street replacement.
•
Replacement of the secondary treatment activated sludge process with Sanitaire, or equal,
conventional activated sludge process (data on the Sanitaire system is included in Appendix E). The
system will provide adequate aeration tank volume (525,000 cu. ft.) for an organic loading of 15
pounds BOD5/day per 1,000 cu. ft. of volume for the projected 20-year BOD5 loading rate of 7,870
ppd (total influent BOD5 loading of 11,238 ppd x 70% = 7,870 ppd assumes 30% BOD5 removal
through the primary clarifiers). Oxygen requirements will be met to provide a dissolved oxygen
concentration of 2.0 mg/l, satisfying the oxygen requirements for BOD5 and ammonia removal. The
system replacement includes:
Aeration
Tanks
Figure 7.5.1 - Sewage Treatment Plant No. 1 - Conventional Activated Sludge
- Four 50-feet-wide by 175-feet-long by 15-feet-deep basins;
- Sanitaire, or equal, ceramic disc diffusers (3,744 discs) with diffuser cleaning system;
- Stainless steel and PVC air header system;
- Air supply piping;
- Three 125-horsepower Continental blowers, or equal, sized for half load service of 2,504 SCFM @
7.3 PSIG, two primary and one back-up, including valves, filters, silencers, etc.
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Harding ESE, Inc.
- Weirs and gates; and
- Influent and effluent piping.
•
Secondary treatment system-clarifier replacement to provide for a peak flow rate of 15.39 MGD with
a SSR of 800 gallon/day/square foot, a solids loading rate of 50 pounds/day/square foot, and a weir
loading rate of 30,000 gallon/day/lineal foot. The proposed system will include the following
components:
- Two 130-foot diameter concrete structures;
- Two 130-foot diameter WESTECH, or equal, clarifier mechanisms, including bridge and aluminum
peripheral hand rail system;
- Scum pump station and forcemain;
- WAS/RAS pumping system and piping;
- Influent and effluent piping; and
- Site and road improvements.
•
Replacement of the chlorination system used for final effluent disinfection with an INFILCO low
pressure/high output ultraviolet light (UV) disinfection system, or equal. The UV system will
include:
- Two 24.5-inch-wide by 26-inch-long by 60-inch-deep concrete channels;
- INFILCO Aquaray  40, with 320 lamps total assuming 65% UV transmission and a dosage at peak
flow of 40,500 watt secs/cm2 or equal;
- In-channel air scrubbing system, including blower assembly;
- Overhead lifting device;
- Channel grating; and
- Slide gates.
•
Improvements to the anaerobic digester system, including:
- Addition of a gravity belt press, 2.2 meter Komline-Sanderson Model G-GRSL Series III
combination belt filter press and gravity belt thickener, or equal, or a Model CA 405 Westfalia
centrifuge or equal, for backup to the existing GBT and sludge lagoons;
- Installation of a second 150 KW dual-gas engine-generator with transfer switch;
- Replacement of the G-1 engine-generator transfer switch;
- Digester gas room improvements, including pipe replacement; and
- Building improvements.
•
Effluent pump station installation for pumping of final effluent during periods of high Illinois River
water levels. The pump station will include:
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Harding ESE, Inc.
- Two 11,000 gpm, 50 hp, vertical turbine solids handling pumps with variable speed drives;
- Concrete pumping chamber;
- Diversion chamber/valve vault; and
- Connection to the existing piping.
Table 7.5.3
STP #1 Upgrade
Conventional Activated Sludge
Item
Preliminary Treatment
Primary Settling
Activated Sludge Process
Disinfection
Sludge Digestion
Sludge Dewatering/Disposal
Effluent Pump Station
Demolition of Structures
Electrical Power & Controls
Subtotal
Contingency
Engineering & Admin.
Estimated Total Construction Cost
Estimated
Cost
$ 245,000
$ 990,000
$2,850,000
$1,000,000
$ 500,000
$ 372,000
$ 356,500
$ 250,000
$ 100,000
$ 300,000
$6,963,500
$ 696,350
$1,140,000
$8,799,850
The estimated total capital cost to construct the conventional activated sludge treatment system is
approximately $8,799,900. For purposes of comparison with other types of secondary treatment systems,
the estimated total annual operation and maintenance (O&M) costs have been calculated for the improved
and expanded conventional activated sludge treatment system operating at a DAF of 6.84 MGD. The
major components of the O&M costs were considered and included, smaller components that would be
fairly consistent with all of the evaluated processes have not been included in the calculated O&M costs.
The estimated annual O&M cost is $768,310, as listed in Table 7.5.4.
The estimated capital cost and annual O&M cost were used to calculate a present worth for the
conventional activated sludge system of $17,612,300. The present worth cost was calculated for 20 years
at a six percent discount rate.
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Harding ESE, Inc.
Table 7.5.4
STP #1 Upgrade - Conventional Activated Sludge
Annual Operation and Maintenance Cost
Item
Labor (See Note 1)
Electric (See Note 2)
- Primary effluent pumps - $22,721
- WAS/RAS pumps - $4,760
- Blowers for aeration system - $77,398
- Anaerobic digester system - $9,737 (See Note 3)
- Primary sludge pumps - $2,595
- Effluent pumps - $1,038 (See Note 4)
- Miscellaneous electric loads - $26,280
- Savings from G-1 power generation - $22,500
Polymer (See Note 5)
Sludge disposal (See Note 6)
UV disinfection, including power costs
Estimated Total Annual O&M Cost
Notes: 1.
2.
3.
4.
5.
6.
7.5.3
Estimated
Cost
$ 340,000
$ 122,029
$ 29,286
$ 259,000
$ 17,995
$ 768,310
Labor costs for five full time positions (cost estimate provided by United Water)
Electric cost based on $0.06/KWH
Anaerobic digester equipment includes two gas compressors, two sludge re-circulation pumps, GBT,
and one brown water pump.
Effluent pump power cost assumes operation of one pump five percent of the year.
Polymer cost = $1.05 per pound for the GBT and centrifuge or belt press. Digested sludge de-watering
of 50 percent of the sludge with the centrifuge or belt press.
Sludge disposal costs include 50 percent land application and 50 percent de-watered and landfilled.
Land application cost = $0.034 per gallon; landfill disposal cost = $0.023 per pound dry weight.
Counter Current Aeration without Primary Treatment
The Counter Current aeration system, shown in Figure 7.5.2 and 7.5.3, designed to provide full treatment
without primary clarifiers was evaluated as an alternative to the conventional activated sludge process.
Staff from the City of Pekin, United Water and Harding ESE visited a Counter Current treatment system
in Clayton County, Georgia, shown in Figure 7.5.3, as part of the system evaluation. This system,
manufactured by Schreiber Corporation, Inc., located in Trussville, Alabama, diffuses air into the
wastewater through submerged fine bubble diffusers attached to a rotating bridge. The air bubbles are
dispersed in a uniform pattern throughout the aeration reactor, eliminating the formation of a vertical
updraft of water which would carry the air bubbles quickly to the surface. The manufacturer claims a
high oxygen transfer rate occurs from moving the diffusers through the wastewater, resulting in power
savings of 35 to 50 percent compared with conventional and mechanical aeration systems.
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Harding ESE, Inc.
With Counter Current aeration, the liquid contents of the tank are aerated in subsequent sections by the
rotating bridge moving around the tank. The rotating aeration bridge brings the light medium (air) to the
heavy medium (water) instead of the usual way of bringing the water to the air. This results in good
mixing and low power requirements for the mixing operation.
With the rotating bridge and diffuser system providing the mixing, the functions of aeration and mixing
are separated. This process matches the oxygen input to the varying organic loads while maintaining an
adequately mixed basin. This has the potential to result in an energy savings through the use of an
organic load monitoring blower control. ( Additional information on the Schreiber Counter Current
System is included in Appendix F.)
Since this treatment alternative does not include primary clarifiers, a more intensive preliminary treatment
system is being proposed. A fine screen system (gap width of ¼ inch) is being proposed along with
replacement of the existing grit system with a separate grit and grease channel system. This preliminary
treatment system will provide a wastewater to the aeration system relatively free of grit, floating debris
and large inorganic solids.
The Counter Current system without primary clarifiers will produce only waste activated sludge (WAS).
Due to potential operational issues associated with anaerobically digesting only WAS, this treatment
alternative will include modification of the existing anaerobic digesters to convert them to aerobic
digesters. The major operational issues of anaerobic digestion using only WAS considered include
potential foaming, and low digester gas production resulting in the need to heat sludge with natural gas.
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Figure 7.5.2 - Counter Current System
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The aeration system proposed by Schreiber includes the following components.
•
Aeration System Model – GRO
•
Number of units – 2
•
Diameter of units – 150 feet
•
Site water depth – 16 feet
•
F:M ratio – 0.080
•
MLSS concentration – 4,000 mg/l
•
Hydraulic detention – 14.84 hours
•
Biological loading rate – 19.84 pounds BOD/1000 cu.ft.
•
Blower model – GM 50L
•
Number of duty blowers – 6
•
Number of standby blowers – 1
•
Blower horsepower each – 75 HP
•
ICFM each – 1,324 ICFM
•
RAS pumps – tube mounted screwpumps
•
Number of RAS pumps – 2
•
Capacity of RAS pumps each – 5,020 gpm @ 5 feet lift
The estimated cost to construct the Counter Current treatment system is approximately $8,253,500, as
detailed in Table 7.5.5. The Counter Current treatment system and other recommended treatment system
improvements evaluated include the following components.
•
Two Schreiber Model DFR-100 Hyrdo-Grid
fine screens, or equal, to be located in the
existing modified influent channels that
presently contain the bar screen and channel
grinder, providing a DAF of 6.84 MGD and a
peak hourly flow of 15.39 MGD. Two
Schrieber RWP-120 Clean Squeeze washer
compactors, or equal, are also proposed with
this system.
•
One Schreiber SFB-440 grit and grease
Figure 7.5.3 - Counter Current
removal system, or equal, at 53 feet in length,
two-GM 4S 5.0 Hp grit blowers and appurtenances, providing a potential DAF of 6.84 MGD and a
peak hourly flow of 15.39 MGD. The grit washer installed in 1999 will be reused.
•
Replacement of all four primary clarifiers with two-85 foot diameter WESTECH, or equal, primary
clarifiers, providing a total surface area of 11,325 square feet. At a surface settling rate (SSR) of
1,200 gallon/day/square foot of tank area, 30 percent BOD removal is expected through the primary
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Harding ESE, Inc.
Figure 7.5.4 – Counter Current System without Primary Clarifiers
- Flow meters;
- Sidewalks;
•
Replacement of the secondary treatment activated sludge process with a Schreiber Counter Current
aeration system. The Schreiber system contains the components described previously in this section.
•
components:
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Harding ESE, Inc.
•
include:
flow of 40,500 uwatt secs/cm2 or equal;
- Slide gates.
•
Improvements to convert the anaerobic digester system, to an aerobic system including:
- Digester gas room demolition;
- Building improvements;
- Digester No. 1, No. 2 and No. 3 conversion to aerobic digesters, including cover modifications,
removal of gas mixing systems, addition of aeration systems and blowers (6-75Hp units) and other
required modifications.
•
- Two - 11,000 gpm, 50 hp, vertical turbine solids handling pumps with variable speed drives;
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Harding ESE, Inc.
Table 7.5.5
STP #1 Upgrade
Counter Current System without Primary Clarifiers
Item
Primary Settling
Disinfection
Sludge Digestion
Subtotal
Contingency
Estimated
Cost
$ 453,000
$
-0$2,500,000
$1,450,000
$ 500,000
$ 650,000
$ 356,500
$ 250,000
$ 100,000
$ 310,000
$6,524,500
$ 652,450
$1,076,500
$8,253,450
The estimated total capital cost to construct the Counter Current System without primary clarifiers is
the estimated total annual operation and maintenance (O&M) costs have been calculated for the Counter
Current treatment system operating at a DAF of 6.84 MGD. The major components of the O&M costs
were considered and included, smaller components that would be fairly consistent with all of the
evaluated processes have not been included in the calculated O&M costs. The estimated annual O&M
cost is $893,951, as listed in Table 7.5.6.
Table 7.5.6
STP #1 Upgrade – Counter Current without Primary Clarifiers
Item
Labor (See Note 1)
- Influent pumps - $22,721
- Aerobic digester system - $77,854 (See Note 3)
Notes: 1.
Estimated
Cost
$ 340,000
$ 247,670
$ 29,286
$ 259,000
$ 17,995
$ 893,951
Labor costs for five full-time positions (cost estimate provided by United Water)
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2.
3.
4.
5.
6.
Aerobic digester equipment includes two sludge re-circulation pumps, GBT, one brown water pump
and blowers for aerobic digesters.
The estimated capital cost and annual O&M cost were used to calculate a present worth for the Counter
Current System without primary clarifiers of $18,507,000. The present worth cost was calculated for 20
years at a 6 percent discount rate.
7.5.4
Counter Current Aeration with Primary Treatment
This alternative includes a Schreiber Counter Current aeration system similar to the one evaluated in
Section 7.5.3, but with the addition of primary clarifiers. (Additional Schreiber Counter Current System
information is included in Appendix F.) Since primary clarifiers are included in the treatment scheme, a
less intensive preliminary treatment system is proposed. The preliminary treatment system will include
replacement of the existing bar screen and channel grinder with a duplex mechanical bar screen system
and the installation of a second grit removal system, similar to the existing aerated grit system. Anaerobic
sludge digestion will be utilized with this system for the primary and waste activated sludge. The
Figure 7.5.5 - Counter Current System with Primary Clarifiers
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estimated cost of the Counter Current treatment system and other plant improvements is listed in Table
7.5.7. A conceptual layout of the treatment plant is shown in Figure 7.5.5. The conceptual layout and
cost estimate are based on the following components.
•
•
Duplicate grit system as the existing and upgrade to existing aerated grit removal system, providing a
potential DAF of 11.4 MGD and a peak hourly flow of 24.0 MGD. The grit washer installed in 1999
will be reused.
•
Replacement of all four primary clarifiers with two 85-foot diameter WESTECH, or equal, primary
clarifiers, providing a total surface area of 11,325 square feet. At a surface settling rate (SSR) of
1,200 gallon/day/square foot of tank area, 30 percent BOD5 removal is expected through the primary
- Flow meters;
- Sidewalks;
•
Replacement of the secondary treatment activated sludge process with the Schreiber Counter Current
System. The system will provide adequate aeration tank volume for the projected 20-year BOD
loading rate of 7,870 ppd (total influent BOD loading of 11,238 ppd x 70% = 7,870 ppd). Oxygen
requirements will be met to provide a dissolved oxygen concentration of 2.0 mg/l, satisfying the
oxygen requirements for BOD and ammonia removal. The system replacement includes:
- Two Schreiber Model GRO aeration units;
- Two concrete structures: 131 feet diameter by 15.0 feet sidewater depth;
- Stainless steel and PVC air header system;
- Air supply piping;
- Six Model GM 35S Aerzen electric blowers; 60 Hp each @ 1,102 ICFM;
- Required weirs and gates; and
- Influent and effluent piping.
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•
components:
•
include:
- Slide gates.
•
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Table 7.5.7
STP #1 Upgrade
Counter Current System with Primary Clarifiers
Item
Primary Settling
Disinfection
Sludge Digestion
Subtotal
Contingency
Estimated
Cost
$ 245,000
$ 990,000
$2,100,000
$1,000,000
$ 500,000
$ 372,000
$ 356,500
$ 250,000
$ 100,000
$ 300,000
$6,213,500
$ 621,350
$1,025,000
$7,859,850
•
The estimated total capital cost to construct the Counter Current system with primary clarifiers is
the estimated total annual operation and maintenance (O&M) costs have been calculated for the Counter
Current System operating at a DAF of 6.84 MGD. The major components of the O&M costs were
considered and included, smaller components that would be fairly consistent with all of the evaluated
processes have not been included in the calculated O&M costs. The estimated annual O&M cost is
$771,520, as listed in Table 7.5.8.
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Table 7.5.8
STP #1 Upgrade – Counter Current with Primary Clarifiers
Item
Labor (See Note 1)
Notes: 1.
2.
3.
4.
5.
6.
Estimated
Cost
$ 340,000
$ 125,240
$ 29,286
$ 259,000
$ 17,995
$ 771,521
The estimated capital cost and annual O&M cost were used to calculate a present worth for the Counter
Current system with primary clarifiers of $16,709,100. The present worth cost was calculated for 20
years at a six percent discount rate.
7.5.5
Sequence Batch Reactor (SBR)
For purposes of evaluation and comparisons with other systems, the Aqua SBR, manufactured by AquaAerobics Systems, Inc., located in Rockford, Illinois has been chosen. Staff from the City of Pekin,
United Water and Harding ESE visited a SBR plant in Clear Lake, Iowa, shown in Figure 7.5.6, as part of
the system evaluation.
Each Aqua SBR unit acts as an equalization basin, aeration basin, and clarifier within a single reactor,
significantly reducing the amount of area required for the treatment system. Normally, the process
follows basic operational steps that include fill, react, settle and decant. The SBR has the ability to create
aerobic or anoxic conditions within the reactor resulting in flexible operation (Additional Aqua SBR
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Harding ESE, Inc.
information is presented in Appendix H.) Aqua-Aerobics Systems, Inc. claim numerous system features
and benefits including the following.
•
Tolerates variable hydraulic loads
•
Tolerates variable organic loads
•
Controls filamentous growth
•
Separate aeration and mixing systems
•
All components retrievable and accessible
•
Return activated sludge pumping eliminated
•
Low installation costs
The SBR produces a waste
activated sludge that will
be most efficiently digested
by aerobic digestion.
Operational issues
discussed in Section
7.5.1.3 related to anaerobic
digestion of WAS, also
apply to the SBR process.
The cost estimate of this
alternative includes
modification of the
anaerobic digesters to
convert them to aerobic
digesters.
Figure 7.5.6 - SBR in Clear Lake, Iowa
Since there are no primary clarifiers in the treatment scheme, a more intensive preliminary treatment
system is proposed to reduce the amount of grit, oil and grease, floatables, and larger debris from entering
the reactor basins. The preliminary treatment system is identical to that described in Section 7.5.1.3.
The Aqua SBR system includes the following design criteria and component sizing:
•
Four basin SBR
•
Basin dimension – 94 feet x 94 feet x 22 feet deep
•
F:M ratio – 0.08 pounds BOD/pounds MLSS – day
•
MLSS concentration – 4,500 mg/l
•
Hydraulic retention – 0.758 days
•
Solids retention – 11.6 days
•
Biological loading rate – 15 pounds BOD/1,000 cu. ft.
•
Mixers – 4-40 Hp Model FSS DDM
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•
WAS transfer pumps – 4-3 Hp submersible
•
Blowers – 5 Roots 824R, 250Hp each
The estimated construction cost for the SBR is detailed in Table 7.5.9. The SBR treatment system and
other plant improvements evaluated in this alternative are shown in Figure 7.5.7 and include the following
components.
•
Two Schreiber Model DFR-100 Hydro-Grid fine screens, or equal, to be located in the existing
modified influent channels that presently contain the bar screen and channel grinder, providing a DAF
of 6.84 MGD and a peak hourly flow of 15.39 MGD.
•
Two Schreiber Model RWP-120 Clean Squeeze washer compactions, or equal;
•
One Schreiber SFB-440 grit and grease removal system, or equal, at 53 feet in length, two-GM 4S 5.0
Hp grit blowers and appurtenances, providing a DAF of 6.84 MGD and a peak hourly flow of 15.39
MGD. Grit washer installed in 1999 will be reused.
Replacement of the primary treatment system, the secondary treatment activated sludge process and the
secondary clarifiers with a four basin SBR as previously described in this section. The SBR system will
provide adequate aeration tank volume for the projected 20-year BOD loading rate of 11,238 ppd.
Oxygen requirements will be met to provide a dissolved oxygen concentration of 2.0 mg/l, satisfying the
oxygen requirements for BOD and ammonia removal.
Figure 7.5.7 - Sequence Batch Reactor (SBR)
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Harding ESE, Inc.
•
include:
- Slide gates.
•
Improvements to convert the anaerobic digester system to an aerobic system, including:
- Digester gas room demolition;
- Building improvements;
- Digester No. 1, No. 2 and No. 3 conversion to aerobic digesters, including cover modifications,
removal of gas mixing systems, addition of aeration systems and blowers (6-75 Hp units) and other
required modifications.
•
The estimated total capital cost to construct the SBR treatment system is approximately $7,785,500. For
purposes of comparison with other types of secondary treatment systems, the estimated total annual
operation and maintenance (O&M) costs have been calculated for the SBR treatment system operating at
a DAF of 6.84 MGD. The major components of the O&M costs were considered and included, smaller
components that would be fairly consistent with all of the evaluated processes have not been included in
the calculated O&M costs. The estimated annual O&M cost is $933,880 as listed in Table 7.5.10.
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Table 7.5.9
STP #1 Upgrade -SBR System
Item
Primary Settling
SBR System
Disinfection
Sludge Digestion
Subtotal
Contingency
Estimated Cost
$ 453,000
$
-0$3,300,000
$
-0$ 530,000
$ 605,000
$ 356,500
$ 250,000
$ 100,000
$ 560,000
$6,154,500
$ 615,450
$1,015,500
$7,785,450
Table 7.5.10
STP #1 Upgrade – SBR System
Item
Labor (See Note 1)
- Influent pumps - $22,721
- WAS pumps - $2,491
- Aerobic digester system - $77,854 (See Note 3)
Notes: 1.
2.
3.
4.
5.
6.
Estimated
Cost
$ 340,000
$ 287,598
$ 29,286
$ 259,000
$ 17,995
$ 933,879
Aerobic digester equipment includes two sludge re-circulation pumps, GBT, one brown water pump,
and blowers for aerobic digestion.
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The estimated capital cost and annual O&M cost were used to calculate a present worth for the SBR
system of $18,496,900. The present worth cost was calculated for 20 years at a six percent discount rate.
7.5.6
Vertical Loop Reactor with Primary Treatment
Initially in this facility planning process, oxidation ditch technology was considered as another alternative
to the conventional activated sludge process. But due to space constraints at the site and
recommendations by Envirex, manufacturer of the Orbal Process, we evaluated Envirex’s Vertical Loop
Reactor (VLR) as a similar process to an oxidation ditch. (Additional VLR information is presented in
Appendix I.)
The VLR has the process kinetics of the Orbal Process with a much smaller footprint. It is essentially an
oxidation ditch on its side, as shown in Figure 7.5.8 and Figure 7.5.9., with each basin being divided into
two compartments, upper and lower. Discs are located in the upper compartment for oxygen delivery and
mixing; coarse bubble diffusers are located in the front part of the lower compartment for supplemental
oxygen delivery. Air in the lower compartment is contained beneath the horizontal divider baffle for the
full length of the tank, substantially increasing the retention time of the air in the liquid, doubling the
oxygen transfer efficiency of the coarse bubble diffuser. The VLR system, using multiple tanks in series,
has the same process benefits of the Orbal Process, including total nitrogen removal, biological
phosphorous removal, stormflow treatment, and DO stratification across multiple reactors for energy
savings.
Flow
Flow
Figure 7.5.8 - Vertical Loop Reactor (VLR) - Section View
Staff from the City of Pekin, United Water and Harding ESE toured a VLR plant in Texas City, Texas,
shown in Figure 7.5.9. The Texas City plant operates at nearly the same flow rate and loadings as the 20
year projected design flows for the City of Pekin.
The VLR system proposed by Envirex and used for costing and comparison purposes includes the
following components.
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Harding ESE, Inc.
•
Four tank VLR system
•
Tank dimensions each – 126 feet long x 30 feet wide x 21 feet deep
•
MLSS concentration – 25% @ 9,000 mg/l; 75% @ 4,500 mg/l
•
Hydraulic detention – 8.07 hours
•
Sludge yield – 1.0
•
Sludge age – 9.8 days
•
Number of discs – 72 per tank
•
Number of diffusers – 100 per tank
•
Biological loading rate – 23 pounds BOD/1,000 cu.ft.
•
Blowers – three 75 Hp blowers – full duty
one 75 Hp blower – standby
•
RAS pumps – tube mounted screw pumps
•
Number of RAS pumps – 2
•
Capacity of RAS pumps each – 5,020 gpm @ 5 feet lift
The VLR system with primary clarifiers will produce primary and waste activated sludge that will be
digested in the existing, improved anaerobic digesters.
The VLR system and other treatment plant improvements evaluated, are shown in Figure 7.5.10 and
include the following components.
•
•
Duplicate grit system as the existing and upgrade the existing aerated grit removal system, providing
a potential DAF of 11.4
MGD and a peak hourly
flow of 24.0 MGD. The
grit washer installed in
1999 will be reused.
•
Replacement of all four
primary clarifiers with two
85-foot diameter
WESTECH, or equal,
primary clarifiers,
providing a total surface
area of 11,325 square feet.
At a surface settling rate
(SSR) of 1,200
gallon/day/square foot of
Figure 7 5 9 - Vertical Loop
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Harding ESE, Inc.
tank area, 30 percent BOD removal is expected through the primary clarifier system at a peak hourly
rate of 15.39 MGD. System replacement includes:
- Flow meters;
- Sidewalks;
•
Replacement of the secondary treatment activated sludge process with the Envirex VLR system
described above. The system will provide adequate aeration tank for the projected 20-year BOD
loading rate of 7,870 ppd (total influent BOD loading of 11,238 ppd x 70% = 7,870 ppd).
Oxygen requirements will be met to provide a dissolved oxygen concentration of 2.0 mg/l,
satisfying the oxygen requirements for BOD and ammonia removal.
Figure 7.5.10 - Vertical Loop Reactor (VLR)
•
components:
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Harding ESE, Inc.
•
include:
- Slide gates.
•
•
- Two - 11,000 gpm, 50 hp, vertical turbine solids handling pumps with variable speed drives;
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Table 7.5.11
STP #1 Upgrade
VLR System
Item
Primary Settling
Disinfection
Sludge Digestion
Subtotal
Contingency
Table 7.5.12
Item
Labor (See Note 1)
Notes: 1.
2.
3.
4.
5.
6.
Estimated
Cost
$ 245,000
$ 990,000
$1,939,000
$1,000,000
$ 500,000
$ 372,000
$ 356,500
$ 250,000
$ 100,000
$ 300,000
$5,552,500
$ 555,250
$ 916,000
$7,023,750
Estimated
Cost
$ 340,000
$ 123,164
$ 29,286
$ 259,000
$ 17,995
$ 769,445
83
Harding ESE, Inc.
The estimated total capital cost to construct the VLR treatment system is approximately $7,023,800 as
detailed in Table 7.5.11. For purposes of comparison with other types of secondary treatment systems,
the estimated total annual operation and maintenance (O&M) costs have been calculated for the VLR
treatment system operating at a DAF of 6.84 MGD. The major components of the O&M costs were
considered and included, smaller components that would be fairly consistent with all of the evaluated
processes have not been included in the calculated O&M costs. The estimated annual O&M cost is
$769,450, as listed in Table 7.5.12.
The estimated capital cost and annual O&M cost were used to calculate a present worth for the VLR
system of $15,849,200. The present worth cost was calculated for 20 years at a six percent discount rate.
7.5.7
STP#1 and STP#2 Upgrades
A previous study, performed by Randolph & Associates, Inc., projected flow to STP#2 in the year 2000 to
reach an average flow of nearly 2.0 MGD, a maximum flow of 4.0 MGD, and a peak flow of 4.8 MGD.
Based on the existing development in the north and east sections of Pekin, these flows appear to be
reasonable. Projecting the flows to 2015 and using the same criteria as was used for the city-wide
wastewater projections, the 2015 flow to Pekin’s STP#2 would be 3.0 MGD design average flow and 8.4
MGD peak hourly flow.
The estimated cost to construct a new STP #2 utilizing either a countercurrent aeration or oxidation ditch
system would be approximately $2.5 million. To meet the total projected flow for the year 2015, STP#1
would be upgraded and STP #2 would be constructed for a total estimated cost of $9.4 million.
The estimated operations and maintenance costs for both STP #1 and STP #2 would be $877,500. The
present worth of upgrading, operating and maintaining both STP #1 and STP #2 is $19,464,800.
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Harding ESE, Inc.
8.0 Improvement Option Selection
8.1
The combined sewer overflow structures are critical to proper operation of the City’s combined sewer
system and in preventing the Illinois River water from entering the system during periods of high river
levels. As discussed in Section 7.1, a majority of the improvements recommended for the various
structures are critical in nature but relatively minor in costs. A description of the improvements for each
of the outfalls is given in Section 7.1.1 through Section 7.1.4 of this report. The improvement description
is not repeated here, but Table 8.1 includes a list of the outfalls and the cost of the recommended
improvements.
Table 8.1
Cost of Proposed Improvements
Combined Sewer Overflow
Caroline Street – Outfall 004
Court Street – Outfall 005
Fayette Street – Outfall 006
State Street – Outfall 003
Total Estimated Costs
8.2
Estimated Improvements Cost
$ 36,200
$ 43,560
$ 22,150
$
-0$ 101,910
Three options were evaluated to improve the cleaning system within the State Street Basin, the primary
operational issue relative to the basin. The three options include the following improvements.
•
Option No. 1 – Aeration system on the floor of the tank to keep the wastewater solids in suspension.
•
Option No. 2 – Flushing system using domestic water, mounted on the basin floor to flush solids to
the drain channel and the wet well to be pumped into the sewer system.
•
Option No. 3 – Flushing system using wastewater, mounted on the basin floor, utilizing one existing
sewage pump to flush the solids to the drain channel and the wet well to be pumped into the sewer
system.
Option No. 3 has been selected based on lowest operational cost and the best anticipated performance.
The estimated cost of this option is approximately $141,000, as detailed in Table 8.2.
85
Harding ESE, Inc.
Table 8.2
State Street Basin
No.
Item
1 8” buried force main
2 8” electric plug valves in
pump house
3 6” electric plug valve
4 Core drill walls for pipes
5 Interior piping
6 Building to house valves
7 Conduit & wiring
8 PLC programming
9 Grinder for flushing water
10 Seeding
8.3
Quantity
100
2
Units
Unit Price
$
50.00
$ 2,500.00
Total Price
$ 5,000.00
$ 5,000.00
LF
EA
10
10
840
250
1
1
1
1
EA
EA
LF
SF
LS
EA
EA
LS
$ 4,500.00
$ 100.00
$
30.00
$
40.00
$ 3,500.00
$ 2,000.00
$14,000.00
$ 500.00
Subtotal
Contingency
Estimated Total
$ 45,000.00
$ 1,000.00
$ 25,200.00
$ 10,000.00
$ 3,500.00
$ 2,000.00
$ 14,000.00
$
500.00
$111,200.00
$ 11,120.00
$ 18,348.00
$140,668.00
FCI Bar Screen
Minor building improvements have been identified at the FCI bar screen facility. These improvements
are described in Section 7.3 of this report and are estimated to cost $19,000, as detailed in Table 8.3.
Table 8.3
FCI Bar Screen
Item
Electrical/Mechanical Improvements, including
lighting, HVAC, and door opener
Overhead door replacement
Painting, sealing, and insulation
Subtotal
Contingency
Estimated Total
8.4
8.4.1
Estimated Cost
$ 7,500
$ 3,000
$ 4,500
$15,000
$ 1,500
$ 2,500
$19,000
Wastewater Treatment
CSO Settling and Chlorination Basin – STP #1
Two options were evaluated in Section 7.4 for improving the ability to clean the sludge and debris that
collects in both the settling and chlorination basins at STP #1. The two options each include the addition
of a pumping station and forcemain for the proposed basin cleaning systems. Option No. 1 includes
electrically operated valves sequenced by a PLC for the cleaning operation of both basins, in addition to
86
Harding ESE, Inc.
Table 8.4
Option 2
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Item
3” header pipes in cl basin
3” plug valves
Fire Hydrants
Nozzles
Pump Station
Seeding
Hose reel & cart
Access ramp to chlorination
chamber
Baffle wall revisions
Quantity
50
250
75
235
3
4
30
1
Units
LF
LF
LF
LF
EA
EA
EA
LS
Unit Price
$
50.00
$
40.00
$
30.00
$
30.00
$ 3,000.00
$ 2,000.00
$
50.00
$ 2,500.00
Total Price
$ 2,500.00
$ 10,000.00
$ 2,250.00
$ 7,050.00
$ 9,000.00
$ 8,000.00
$ 1,500.00
$ 2,500.00
1
25
2
1
1
1
1
EA
SF
EA
LS
LS
EA
LS
$ 63,000.00
$
5.00
$
500.00
$ 5,000.00
$ 1,000.00
$ 2,000.00
$17,500.00
$ 63,000.00
$
125.00
$ 1,000.00
$ 5,000.00
$ 1,000.00
$ 2,000.00
$17,500.00
4
EA
$1,500.00
Subtotal
Contingency
Estimated Total
$1,500.00
$138,425.00
$ 13,842.50
$ 22,850.00
$175,117.50
supplemental manual hose flushing and mechanical sludge removal. Option No. 2 includes the addition
of a ramp to access the chlorination basin for mechanical cleaning with a small skid loader and manual
hose flushing hydrants located in both basins.
Option No. 2 is the recommended improvement due to a lower capital cost, less complicated process, and
the best anticipated performance. The estimated cost of Option No. 2 improvements is $175,118 as
detailed in Table 8.4.
8.4.2
Treatment Systems
Five treatment system alternatives were considered for expansion of STP #1, in addition to an option that
included improving STP #1 and replacing STP #2.
The following options were considered.
•
STP #1 expansion conventional activated sludge
•
STP #1 expansion Counter Current aeration (Schreiber) without primary treatment
87
Harding ESE, Inc.
•
STP #1 expansion – Counter Current aeration (Schreiber) with primary treatment
•
STP #1 expansion – Sequence Batch Reactor (SBR)
•
STP #1 expansion – Vertical Loop Reactor (VLR)
•
STP #1 improvement and STP #2 replacement
Each of these options was discussed in detail in Section 7.5 of this report, therefore they will not be
repeated in this section.
The evaluation of the various treatment processes was performed as a joint effort of the City of Pekin,
United Water and Harding ESE. The primary elements of this evaluation include the following items.
•
Preliminary design and information gathered from manufacturers on the various processes.
•
Process components sized to adequately treat the City of Pekin’s projected wastewater loading.
•
Site visits to similar treatment plants as being considered for Pekin.
•
Conceptual treatment plant design for each treatment scheme, including conceptual drawing,
preliminary construction cost estimate, and preliminary operation and maintenance costs.
•
Present worth calculation for a 20-year period for each option considered.
•
Consideration of operational and maintenance issues, exclusive of costs.
The treatment plant option selected is STP #1 expansion with the Envirex Vertical Loop Reactor (VLR),
as described in Section 7.5.1.6. As listed in Table 8.5, the VLR option has a construction cost of
$7,023,750, the lowest of all of the alternatives, and the second lowest operation and maintenance cost of
$769,450. The 20-year present worth for the VLR system, based on a six percent discount rate is
$15,849,200, the lowest of all options evaluated.
Table 8.5
Summary of Costs Analysis – Treatment
Alternatives
Conv. Activated Sludge
Counter Current w/o Pr.
Counter Current
Sequence Batch Reactor
Vertical Loop Reactor
STP #1 Improvement and
STP #2 Replacement
Capital Costs
$8,799,850
$8,253,450
$7,859,850
$7,785,450
$7,023,750
$9,400,000
O & M Costs
$768,310
$893,950
$771,520
$933,880
$769,450
$877,500
Present Worth
$17,612,300
$18,507,000
$16,709,100
$18,496,900
$15,849,200
$19,464,800
Exclusive of cost issues, the VLR was also chosen due to the following criteria.
•
Small system footprint
•
Flexible modes of operation through the four basins
•
Similar plants with records of the VLR’s ability to tolerate variable hydraulic and organic loads
•
Minimal maintenance requirements
88
Harding ESE, Inc.
•
Flexibility to operate the basins at independent variable DO concentrations
•
Impressive record of experience, including operator references
The VLR system was described in Section 7.5.1.6, including conceptual drawing, construction cost
estimate and operation and maintenance cost projection while operating at DAF. The cost detail is
repeated in Table 8.6 for reference.
Table 8.6
STP #1 Upgrade
VLR System
Item
Primary Settling
Disinfection
Sludge Digestion
Subtotal
Contingency
89
Estimated Cost
$ 245,000
$ 990,000
$1,939,000
$1,000,000
$ 500,000
$ 372,000
$ 356,500
$ 250,000
$ 100,000
$ 300,000
$5,552,500
$ 555,250
$ 916,000
$7,023,750
Harding ESE, Inc.

City of Pekin Wastewater Facility Plan

Transcription

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