Removal of MTBE from Drinking Water Using Air Stripping: Case

Transcription

Removal of MTBE from Drinking Water
Using Air Stripping: Case Studies
A Publication of:
The California MTBE Research Partnership
Association of California Water Agencies
Oxygenated Fuels Association
Western States Petroleum Association
National Water Research Institute
October 2006
Published by the
National Water Research Institute
NWRI-2006-03
10500 Ellis Avenue ✦ P.O. Box 20865
Fountain Valley, California 92728-0865
(741) 378-3278 ✦ Fax: (714) 378-3375
www.NWRI-USA.org
Limitations
This document was prepared by Malcolm Pirnie, Inc. and is intended for use by members of
the California MTBE Research Partnership (Partnership) pursuant to the Partnership
agreement. Malcolm Pirnie and the Partnership do not warrant, guarantee, or attest to the
accuracy or completeness of the data, interpretations, practices, conclusions, suggestions, or
recommendations contained herein. Use of this document, or reliance on any information
contained herein, by any party or entity other than members of the Partnership, is at the sole
risk of such parties or entities.
i
Acknowledgements
This report was prepared by Rula Deeb, Elisabeth Hawley, Andrew Stocking, Michael
Kavanaugh, Amparo Flores, Stephanie Sue, Douglas Spiers, Michael Wooden, Gerald
Crawford, and Guillermo Garcia of Malcolm Pirnie, Inc. The authors would like to
acknowledge Rey Rodriguez (H2O·R2 Consulting Engineers, Inc.) and Jim Davidson
(currently with Exponent, formerly of Alpine Environmental) for their assistance in
collecting the data discussed in this report.
The authors would like to thank the California MTBE Research Partnership and the National
Water Research Institute (NWRI) for sponsoring this work. The authors especially wish to
acknowledge Ronald Linsky (1934-2005), former Executive Director of NWRI, for his
excellent leadership of the Partnership and for his direction and support of this work. The
authors are also grateful to the many members of the Partnership's Research Advisory
Committee who provided valuable support and review, especially David Pierce
(ChevronTexaco Energy Research and Technology Co.) and Bill Reetz (Kansas Department
of Health and Environment).
ii
Table of Contents
Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Research Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 Research Approach. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4 Report Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2. Air Stripper Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1 Packed Tower Air Stripper – Lacrosse, Kansas
........................
7
2.2 Low Profile Air Stripper – Somersworth, New Hampshire . . . . . . . . . . . . . 11
2.3 Packed Tower Air Stripper – Culver City, California
..................
15
2.4 Low Profile Air Stripper – Bridgeport, Connecticut . . . . . . . . . . . . . . . . . . . 22
2.5 Low Profile Air Stripper – Chester, New Jersey . . . . . . . . . . . . . . . . . . . . . . 27
2.6 Packed Tower Air Strippers – Ridgewood, New Jersey
................
29
2.7 Packed Tower Air Stripper – Rockaway Township, New Jersey . . . . . . . . . 32
2.8 Low Profile Air Stripper – Mammoth Lakes, California . . . . . . . . . . . . . . . 38
2.9 Low Profile Air Stripper – Elmira, California . . . . . . . . . . . . . . . . . . . . . . . . 40
3. Analysis Of System Cost And Performance . . . . . . . . . . . . . . . . . . . . . . . 46
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.2 Treatment Train Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.3 Treatment System Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
..........................................
53
..................................................
54
3.4 Treatment System Costs
4. Model Evaluation
4.1 Overview of Modeling Software Programs
..........................
54
4.2 Low Profile Air Stripper – Somersworth, New Hampshire . . . . . . . . . . . . . 55
4.3 Low Profile Air Stripper – Chester, New Jersey . . . . . . . . . . . . . . . . . . . . . . 56
4.4 Packed Tower Air Stripper – Lacrosse, Kansas . . . . . . . . . . . . . . . . . . . . . . . 56
4.5 Packed Tower Air Stripper – Culver City, California
..................
57
4.6 Packed Tower Air Stripper – Rockaway Township, New Jersey . . . . . . . . . 58
4.7 Summary of Modeling Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
iii
5. Summary Of Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
5.1 Case Study Data Collection
.......................................
60
5.2 Case Study Data Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
5.3 Model Validation
................................................
61
5.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Appendices
Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Appendix B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
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Tables
1
Timeline for Remediation and Treatment at LaCrosse, Kansas . . . . . . . . . 7
2
Average Influent Water Quality Parameters at LaCrosse, Kansas . . . . . . . 8
3
Design/Operating Parameters for Packed Tower at LaCrosse, Kansas . . . 9
4
Capital and Annual O&M Costs (1997) at LaCrosse, Kansas . . . . . . . . . . 12
5
Timeline for Remediation and Treatment at
Somersworth, New Hampshire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6
Average Influent Water Quality Parameters at
7
Design/Operating Parameters for Low Profile Air Stripper at
8
Capital and Annual O&M Costs (1996) at Somersworth, New Hampshire . . . 16
9
Average Influent Water Quality Parameters at Culver City, California . . . 17
10
NPDES Permit Limitations at Culver City, California
11
Design/Operating Parameters for Packed Tower Air Stripper at
Culver City, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
12
Influent Contaminant Design Criteria at Culver City, California
.......
18
13
Influent Hydrocarbon Concentrations at Culver City, California
.......
19
14
Air Stripper Performance Data for MTBE at Culver City, California. . . . 20
15
Capital and Annual O&M Costs (1999) at Culver City, California . . . . . . 22
16
Average Influent Water Quality Parameters at Bridgeport, Connecticut . . . 23
17
Bridgeport, Connecticut . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
18
Air Stripper Performance Data for MTBE at Bridgeport, Connecticut
19
Air Stripper Performance Data for BTEX Compounds at
20
Capital and Annual O&M Costs (1995) at Bridgeport, Connecticut. . . . . 27
21
Average Influent Water Quality Parameters at Chester, New Jersey . . . . . 28
22
Chester, New Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
23
Capital and Annual O&M Costs (1998) at Chester, New Jersey . . . . . . . . 29
v
................
..
18
24
24
Average Influent Water Quality Parameters at Ridgewood, New Jersey . . . 29
25
Design/Operating Parameters for Packed Tower Air Stripper at
Ridgewood, New Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
26
Capital and Annual O&M Costs (1991, 1997) at
Ridgewood, New Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
27
Design/Operating Parameters for Packed Air Stripping Tower at
Rockaway Township, New Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
28
VOC Criteria for 1995 Air Stripping Tower at
29
Average Influent Water Quality Parameters at
30
Capital and Annual O&M Costs (1995) at
31
Timeline of Events at Mammoth Lakes, California . . . . . . . . . . . . . . . . . . . 39
32
Influent Constituent Concentrations at Mammoth Lakes, California . . . . 39
33
MTBE Air Stripping Performance Data at Mammoth Lakes, California . . . 40
34
MTBE Off-Gas Treatment Performance Data at
Mammoth Lakes, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
35
Timeline of Remediation at Elmira, California
36
Average Influent Water Quality Parameters at Elmira, California . . . . . . . 41
37a
Design/Operating Parameters for the Low Profile Air Stripper at
Elmira, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
37b
Design/Operating Parameters for the Off-Gas Treatment System
(ADDOXTM) at Elmira, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
38
Capital and Annual O&M Costs (1997) at Elmira, California . . . . . . . . . . 45
39
Comparison of the Design Parameters, Performance, and Costs
Associated with each of the Packed Tower Air Stripper Systems
......................
.......
41
46
40
Comparison of the Design Parameters, Performance, and Costs
Associated with each of the Low Profile Air Stripper Systems . . . . . . . . . 48
41
Modeling Scenarios for Low Profile Air Stripper at
42
Modeling Scenarios for Packed Tower Air Stripper at LaCrosse, Kansas. . . 57
43
Modeling Scenarios for Packed Tower Air Stripper at
vi
A-1 Air Stripper Performance Data for MTBE at LaCrosse, Kansas . . . . . . . . 65
A-2 Air Stripper Performance Data for MTBE at
A-3 Air Stripper Performance Data for MTBE at Culver City, California. . . . 69
A-4a Air Stripper Performance Data for MTBE at Bridgeport, Connecticut
..
70
A-4b Air Stripper Performance Data for BTEX at
A-5 Air Stripper Performance Data for MTBE at
A-6 Off-Gas System Performance Data for MTBE at Elmira, California . . . . 73
B-1
Modeling Data Comparison for Low Profile Air Stripper at
B-2
Modeling Data Comparison for Packed Tower Air Stripper at
LaCrosse, Kansas
(Water Flow Rate = 480 gpm, Air to Water Ratio = 156) . . . . . . . . . . . . . . 76
B-3
LaCrosse, Kansas
(Water Flow Rate = 350 gpm, Air to Water Ratio = 214) . . . . . . . . . . . . . . 77
B-4
Culver City, California . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
B-5
vii
Figures
1
MTBE concentrations at LaCrosse, Kansas. . . . . . . . . . . . . . . . . . . . . . . . . . 10
2
Removal efficiency reliability at LaCrosse, Kansas. . . . . . . . . . . . . . . . . . . 11
3
MTBE concentrations at Somersworth, New Hampshire.
4
MTBE removal efficiency at Somersworth, New Hampshire. . . . . . . . . . . 14
5
Removal efficiency reliability at Somersworth, New Hampshire. . . . . . . . 15
6
MTBE concentrations at Culver City, California.
7
MTBE removal efficiency at Culver City, California. . . . . . . . . . . . . . . . . . 20
8
Air stripping performance at Culver City, California. . . . . . . . . . . . . . . . . . 21
9
MTBE concentrations at Bridgeport, Connecticut. . . . . . . . . . . . . . . . . . . . 25
10a
MTBE removal efficiency at Bridgeport, Connecticut.. . . . . . . . . . . . . . . . 25
10b
BTEX removal efficiency at Bridgeport, Connecticut. . . . . . . . . . . . . . . . . 26
11
Removal efficiency reliability at Bridgeport, Connecticut.. . . . . . . . . . . . . 26
12
MTBE concentrations versus time at Rockaway, New Jersey. . . . . . . . . . . 35
13
MTBE removal efficiency versus time at Rockaway, New Jersey.
14
Removal efficiency reliability at Rockaway, New Jersey. . . . . . . . . . . . . . . 36
15
MTBE influent concentrations at Elmira, California. . . . . . . . . . . . . . . . . . 43
16
Off-gas treatment influent concentrations of BTEX and TPH-G
(1998 to 2000) at Elmira, California. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
17
ADDOXTM performance summary test data at Elmira, California. . . . . . . 44
18
Cost summary of MTBE removal by air stripping. . . . . . . . . . . . . . . . . . . . 53
19
Comparison of modeling results to actual performance.. . . . . . . . . . . . . . . 59
viii
.............
....................
......
14
19
36
List of Acronyms, Symbols, and Abbreviations
ASAPTM
BTEX
CaCO3
cfm
DCE
DIPE
ETBE
GAC
gpm
Hp
H2O2
kwh
LUST
MTBE
µg/L
mg/L
NEEP
NHDES
NPDES
O&M
PCE
ppbv
ppmv
scfm
StEPP
SVE
TAME
TBA
TCE
TPH-D
TPH-G
USEPA
UST
UV
VOC
Aeration System Analysis Program
Benzene, toluene, ethylbenzene, and xylenes (o-, m-, p-xylene)
Calcium carbonate
Cubic feet per minute
Dichloroethylene
Di-isopropyl ether
Ethyl tertiary butyl ether
Granular activated carbon
Gallons per minute
Horsepower
Hydrogen peroxide
Kilowatt hour
Leaking underground storage tank
Methyl tertiary butyl ether
Microgram per liter
Milligram per liter
North East Environmental Products
New Hampshire Department of Environmental Services
National Pollutant Discharge Elimination System
Operation and maintenance
Perchloroethylene
Parts per billion by volume
Parts per million by volume
Standard cubic feet per minute
Software to Estimate Physical Properties
Soil vapor extraction
Tertiary amyl methyl ether
Tertiary butyl alcohol
Trichloroethylene
Total petroleum hydrocarbons quantified as diesel
Total petroleum hydrocarbons quantified as gasoline
U.S. Environmental Protection Agency
Underground storage tank
Ultraviolet
Volatile organic compound
ix
x
Executive Summary
In response to an identified research need to assess the performance of air stripping to
remove methyl tertiary butyl ether (MTBE) from contaminated groundwater, the California
MTBE Research Partnership undertook this project to:
• Collect design, performance, and cost summary data from several packed tower and low
profile air stripper treatment systems addressing MTBE contamination in groundwater
supplies.
• Use the data from these case studies to develop a series of cost and reliability curves.
• Assess the accuracy of several available models used to predict the cost and performance
of packed tower and low profile air strippers.
Data from nine case study sites operating during the late 1990s were obtained and analyzed.
Two models were chosen for evaluation: the Aeration System Analysis Program (ASAPTM)
Packed Tower Model and the North East Environmental Products (NEEP) ShallowTray®
Modeler software.
Results indicate that a variety of different treatment train configurations can use air strippers
to successfully remove a wide range of MTBE concentrations (i.e., from 10 to 2,400,000
micrograms per liter [µg/L]). Removal efficiencies ranged from 65 percent to greater than
99.9 percent.
Capital costs (expressed in year 2000 dollars) ranged from $0.47/1,000 to $104/1,000 gallons
system capacity. Operation and maintenance (O&M) costs were a function of flowrate and
percent MTBE removal. Annual O&M costs ranged from $1/1,000 to $10/1,000 gallons to
achieve greater than 90-percent removal and from $0.15/1,000 to $1/1,000 gallons to achieve
greater than 65-percent removal.
Commercially available models were found to predict actual removal efficiencies within
15 percent, demonstrating that modeling can be a valuable tool for assessing air stripper cost
and performance during conceptual design or remedy selection
1
2
1. Introduction
1.1 Background
In 1995, the Lawrence Livermore National Laboratory reported that greater than 90 percent
of the groundwater plumes (defined as the 10 micrograms per liter [µg/L] benzene isoconcentration level) emanating from underground storage tank (UST) gasoline releases in California
were likely to stabilize (i.e., stop increasing in size) at distances less than 250 feet downgradient of leaking underground storage tank (LUST) releases (Rice et al., 1995). These
plumes — identified primarily by one or more benzene, toluene, ethylbenzene, and xylene
(BTEX) components — moved slowly and eventually stabilized due to natural biodegradation
and retardation. Lawrence Livermore National Laboratory concluded that many BTEX
plumes might not require active remediation due to these natural attenuating processes and
that monitored natural attenuation could be a remedial strategy at many UST sites in
California and other states.
Shortly thereafter, methyl tertiary butyl ether (MTBE), an oxygenate added to gasoline to
increase octane levels and to meet federal and state fuel specifications for oxygen content,
was detected in drinking water wells in the City of Santa Monica, California (US Water
News, 1996). This discovery caused regulatory agencies in California to immediately
reassess cleanup strategies at gasoline UST sites. Groundwater samples collected at UST
sites in California and elsewhere confirmed MTBE occurrence and, with it, new remediation
challenges for UST owners.
Some of the remediation challenges are apparent from MTBE’s physical and chemical
properties. MTBE is highly soluble in water, is only weakly sorbed to most soils, and exhibits
a low tendency to volatilize from water. Consequently, MTBE partitions relatively easily into
water from a gasoline/MTBE mixture, moves approximately at the rate of groundwater flow,
and — if no active remediation is undertaken — can threaten downgradient water supply
wells. Moreover, depending on the release scenario, MTBE may move farther than BTEX
compounds, ultimately impacting a larger volume of groundwater compared to BTEX-only
plumes. The ether structure of MTBE is not very susceptible to biodegradation. MTBE and
other ether oxygenates were initially found to be resistant to biodegradation, thereby limiting
the use of natural attenuation for contaminated groundwater cleanup at UST sites (Suflita and
Mormile, 1993; Yeh and Novak, 1995). These characteristics of MTBE have increased the
need for active remediation technologies at UST sites and the level of interest in the cost and
performance of available ex situ groundwater treatment technologies. For example, the need
for information on drinking water treatment technologies for MTBE was highlighted in a
U.S. Environmental Protection Agency (USEPA) report titled “Oxygenates in Water: Critical
Information and Research Needs” (U.S. Environmental Protection Agency, 1998).
In February 2000, the California MTBE Research Partnership (Partnership) published a
report summarizing the feasibility of using several technologies to remove MTBE from
3
drinking water (California MTBE Research Partnership, 2000). This report contained a
theoretical analysis of treatment technologies with some reference to field applications. To
further elucidate the ability of these technologies to remove MTBE from drinking water, the
Partnership also funded efforts to gather information from field applications to verify the
estimated cost and efficiency of these technologies to remove MTBE from contaminated
water. For example, the Partnership published two reports focusing on MTBE removal using
synthetic resins (California MTBE Research Partnership, 1999) and granular activated
carbon (California MTBE Research Partnership, 2001). Recently, the Partnership published
a comprehensive evaluation of MTBE remediation options (California MTBE Research
Partnership, 2004). Additional data on MTBE treatment systems and costs is available
through the USEPA’s Technology Innovation Office (U.S. Environmental Protection Agency,
2005) and the Partnership.
Air stripping is a well-established technology for removing volatile organic compounds
(VOCs) from groundwater. Two configurations of air strippers include the low profile and
packed tower systems. In a low profile aeration system, contaminated water is pumped to the
top of the stripper, where it flows over an inlet weir onto a baffled aeration tray. Air is forced
upward through perforations in the tray bottom, creating highly turbulent conditions to
maximize the contact of water and air. In a packed tower air stripping system, contaminated
water passes downward by gravity through a circular or rectangular column that is filled with
either randomly packed or structured packing material. Air is introduced into the tower below
the packed bed and flows upward through the column countercurrent to the flow of water.
The successful and cost-effective application of air stripping to remove MTBE has not yet
been demonstrated or widely accepted. The Partnership identified a research need to evaluate
the effectiveness of air stripping for MTBE removal from groundwater, including actual cost
and performance data from operating groundwater treatment systems. Air stripping system
performance and cost data were collected between 1995 and 2001, at the same time as the
collection of data for two other published Partnership reports (California MTBE Research
Partnership, 1999, 2001). The analysis of these data is presented in this report. Between 2001
and 2005, numerous air strippers — both packed tower and shallow tray configurations —
have been successfully used for both municipal drinking water treatment and remedial
applications. The installation of these treatment systems has contributed to the recognition of
air stripping as a cost-effective option for MTBE treatment. However, a summary of cost and
performance data for MTBE removal via air stripping has still not been published, to our
knowledge. Therefore, the summary presented in this report is unique.
1.2 Research Objectives
The overall objective of the work summarized in this report is to evaluate the cost and
performance of air strippers and associated off-gas treatment systems for removing MTBE
from groundwater supplies. The primary objectives of the project include:
4
• Collect performance data, water quality information, and cost summaries for several
packed tower and low profile air strippers and their respective off-gas treatment processes
for treating MTBE.
• Use the data from these case studies to develop a series of cost curves and reliability curves
for packed tower and low profile air strippers as a function of removal efficiency, flow rate,
and water quality. Identify the most sensitive parameters (e.g., water quality) that influence
the cost and reliability of air stripping systems.
• Identify several available models used to estimate the cost and performance of packed
tower air strippers and low profile air strippers. Use the performance data to assess the
accuracy of the predictions generated by these models.
Due to data limitations, the objectives were not fully met. For example, off-gas treatment
system performance data were not available at every site. Data were not sufficient to conduct
a quantitative sensitivity analysis of the most important parameters impacting air stripper
performance. Thus, a qualitative review of air stripper operational and maintenance
challenges was conducted.
1.3 Research Approach
To evaluate the cost and performance of air stripping for MTBE, data from nine case studies
were examined. At each site, air stripping was used to remove MTBE from contaminated
groundwater. Five of the sites used low profile air strippers, and the other four sites used
packed tower air strippers. The case studies included:
1. Packed tower air stripper — LaCrosse, Kansas
2. Low profile air stripper — Somersworth, New Hampshire
3. Packed tower air stripper — Culver City, California
4. Low profile air stripper — Bridgeport, Connecticut
5. Low profile air stripper — Chester, New Jersey
6. Packed tower air stripper — Ridgewood, New Jersey
7. Packed tower air stripper — Rockaway Township, New Jersey
8. Low profile air stripper — Mammoth Lakes, California
9. Low profile air stripper — Elmira, California
Data for this study were provided by environmental consultants, air stripper manufacturers,
and regulators. At some of the sites, cost and performance data could not be shared with the
Partnership due to ongoing litigation.
The site background, description of the air stripping system, system performance, and
technology cost were summarized for each site. System design parameters were tabulated
5
and performance data were plotted. Similarities and differences between the case studies
were examined. For example, the treatment train design, performance, maintenance
requirements, and costs were compared to identify common elements and potential
additional considerations impacting system performance and cost. Cost data were expressed
in year 2000 dollars and were normalized by flow rate to facilitate comparisons between
different case study sites.
Two commercially available and widely used models for air stripping performance were
evaluated to assess the accuracy of their predictions. Case study parameters (e.g., flow rate,
water temperature, reactor size, and influent contaminant concentrations) were entered into
each model. Model predictions were compared with actual measurements of effluent water
quality at case study sites.
1.4 Report Overview
The research approach provided the framework for the organization of this report.
Section 2 presents the data collected for each of the air stripping systems and associated offgas treatment, and includes a summary of site history, air stripper design, and operating data.
Section 3 presents a summary of cost and performance trends for air stripping that were
identified during the case study data analysis, including system operating parameters,
percent MTBE removal, and unit costs (normalized by system flow rate). The most critical
operating parameters for reducing costs and increasing system reliability were identified.
Section 4 describes two models that are commonly used for predicting air stripper system
cost and performance: the Aeration System Analysis Program (ASAPTM) Packed Tower
Model and the North East Environmental Products (NEEP) ShallowTray® Modeler software.
Key model input parameters and model-predicted system performance are summarized in
this section. Modeling predictions are compared with actual system operating parameters to
evaluate the accuracy of these models.
Section 5 summarizes the main findings of this report and presents strategies for predicting
whether or not air stripping will be a cost-effective and reliable treatment strategy for
removing MTBE and other VOCs from groundwater at a given site.
Section 6 contains a list of publications and other data referenced in this report.
6
2. Air Stripper Case Studies
2.1 PACKED TOWER AIR STRIPPER — LACROSSE, KANSAS
2.1.1 Site Background
In 1992, three gasoline service stations in LaCrosse, Kansas, were identified as sources of
soil and co-mingled groundwater contamination. The LUSTs at each of these three sites
resulted in free-phase gasoline product and a petroleum hydrocarbon plume with MTBE
concentrations exceeding 55,000 µg/L. The extent of groundwater contamination was
characterized using numerous shallow monitoring wells. Sampling results indicated that the
BTEX plume extended approximately 800 feet downgradient of the gasoline station tanks. A
remediation system consisting of soil vapor extraction (SVE), groundwater pump-and-treat,
and product recovery using skimmer pumps was installed in late 1995/early 1996. Due to the
proximity of nearby receptors, the pump-and-treat and product recovery systems were kept
in operation to provide hydraulic containment. The timeline of events related to remediation
and treatment is presented in Table 1.
Table 1. Timeline for Remediation and Treatment at LaCrosse, Kansas
Milestone/Event
Date
Irrigation well sample
February 17, 1997
Public water supply sample
April 7, 1997
City notification
April 23, 1997
Installation of temporary low profile stripper
April 24, 1997
Additional (deeper) wells drilled
April 24, 1997
®
ORC installation
May 10, 1997
Permanent air stripper towers turned on
September 16, 1997
Soil excavations
August 17, 1998
SVE/sparge on
November 13, 1998
Additional deep aquifer sparge on
September 1, 1999
ORC®: Oxygen release compound.
In January 1997, a nearby resident complained of a chemical odor coming from an irrigation
well located less than a mile downgradient of the gasoline service stations. Analytical studies
confirmed that MTBE was present in the well at a concentration of 2,100 µg/L. Two adjacent
municipal wells were subsequently sampled and were also found to be contaminated with
MTBE concentrations of up to 1,050 µg/L. Because the two municipal wells were the only
source of water for the community, an emergency response was formulated to notify local
officials and evaluate treatment options.
Additional monitoring wells were installed between the source area and municipal wells to
confirm that contamination was coming from the three service stations. Nested wells were
drilled to the base of the aquifer and screened at the same depth as the two public supply
7
wells (50 to 70 feet below ground surface [bgs]). Groundwater analytical data from the
nested wells revealed high concentrations of MTBE (up to 1,290 µg/L) in the deeper wells,
with lower to non-detectable concentrations in the shallow wells.
2.1.2 Description of Air Stripping System
Since the two municipal wells were the only sources of potable water for a nearby
community, a treatment system had to be quickly designed to ensure that the wells could
continue to operate. Initially, a five-tray air stripper from the gasoline station pump-and-treat
system installation was relocated to the water treatment facility as an emergency response
measure to remove MTBE from the groundwater prior to water distribution. The tray stripper
was designed to extract water from the clear well at one end and return the treated water at
the opposite end. This pumping arrangement allowed a circulation of treated and raw water,
which diluted MTBE concentrations in the water prior to its delivery into the distribution
system. Flow rates into the tray stripper were limited to 250 gallons per minute (gpm). The
tray stripper was used for 5 months until the packed tower air stripper system was installed.
The permanent air stripping system was designed to treat up to 500 gpm. Influent water
quality parameters are presented in Table 2. The influent to the permanent air stripping
system is pre-chlorinated (0.5 to 1.0 milligrams per liter [mg/L] as residual) at each municipal
well. Prior to entering the air stripping unit, the water is softened with lime, decreasing
hardness from approximately 700 to 110 mg/L as calcium carbonate (CaCO3), and routed
into a settling basin for flocculation. It is then pumped into air stripper towers. Water exiting
the packed towers is recycled back into the settling basin. Overflow water from the settling
basin is directed through a sand and anthracite filter bed, then into a 200,000-gallon
underground clear well and the distribution system.
Table 2. Average Influent Water Quality Parameters at LaCrosse, Kansas
Water Quality Parameter
Concentration
Alkalinity as CaCO3 (mg/L)
131
Aluminum (mg/L)
432
Chloride (mg/L)
127
Corrosivity (mg/L)
0.17
Iron (mg/L)
0.021
Magnesium (mg/L)
17
Nitrate (mg/L)
0.07
Sulfate (mg/L)
347
Total dissolved solids (mg/L)
858
Hardness (mg/L)
115
Turbidity (NTU)
<0.5
pH
8.7
Temperature
Not available
NTU: Nepheleometric turbidity unit.
8
The permanent stripping system consists of two 33-foot tall, 6-foot diameter packed towers.
The towers are partially enclosed within a steel pre-engineered building and contain 21 feet
of 2-inch Jaeger TripackTM packing material. The two units are operated in series to provide
redundancy. The first packed tower air stripper is designed to decrease MTBE concentrations
from up to 1,000 µg/L to less than 20 µg/L, while the second tower is used for water quality
polishing to meet a treatment goal of less than 10 µg/L. The system flow rate ranges from
350 to 480 gpm (in summer months). The blowers can circulate 11,500 cubic feet per minute
(cfm) of air through each tower. The air-to-water design ratio is 150 to 1. Other important
design and operating parameters for the air stripping system are presented in Table 3. The air
strippers are operated by city employees during normal pumping hours (8 am to 4 pm, 6 days
per week). Sampling and routine maintenance duties are performed by facility employees
with as-needed contractor support.
Table 3. Design/Operating Parameters for Packed Tower at LaCrosse, Kansas
Parameter
Design
Tower specifications
6-feet diameter x 33-feet tall Fiberglass
Operating
Packing material
2-inch Jaeger Tri-Pack filled to 21 feet
Configuration
Two towers in parallel
Blower size (Hp)
2 x 15
Pump size (Hp)
3 x 15
Water flow rate (gpm)
500
Air flow rate (cfm)
10,000
Air-water ratio
150:1
156:1 to 214:1
Maximum MTBE concentration (µg/L)
1,000
973
Average MTBE concentration (µg/L)
—
141
Maximum BTEX concentration (µg/L)
Non-detect
Non-detect
MTBE treatment goal (µg/L)
<10
<10
Removal efficiency (%)
90
84
Two towers in series
480 in summer
350 in winter
All off-gases released from the packed tower air strippers are directly discharged into the
atmosphere without treatment.
2.1.3 Air Stripping System Performance
Temporary Tray Strippers
The five-tray air stripper reduced influent MTBE concentrations (200 to 600 µg/L) by an
average of 40 percent. Effluent MTBE concentrations from the tray strippers ranged from 17
to 375 µg/L. The system operated as an emergency response measure until the packed tower
air stripper was installed.
9
Permanent Packed Tower Air Strippers
MTBE influent concentrations ranged from non-detect (less than 10 µg/L) to 973 µg/L. In
most cases (greater than 90 percent of the time), effluent MTBE concentrations were less
than 10 µg/L. The removal efficiency of the air strippers averaged 84 percent over the period
of operation between 1997 and 2000. No significant operation and maintenance (O&M)
problems have been reported to date, and there have been no problems with fouling or
scaling. Manholes on the side of each tower provide visible evidence that the tower packing
material has remained clean. System pressures in each tower have been stable since startup.
MTBE Concentration (µg/L)
The results of sampling events from the temporary tray air strippers (April 25, 1997, to
September 10, 1997) and packed tower air strippers (September 16, 1997, to early 2000) are
presented in Figure 1. The removal efficiency reliability for the two towers is presented in
Figure 1.
MTBE concentrations at LaCrosse, Kansas.
Figure 2. Samples of the influent, first stripper effluent, second stripper effluent, and tap
water are collected on a monthly basis. Detailed performance data is contained in Table A-1
of Appendix A. Total removal rates for MTBE average 95 percent after the second air stripper
tower. As can be seen from available data (Figure 1), occasional spikes in MTBE
concentrations are apparent in the influent water quality, which may be related to the use of
a second public water supply well on Saturdays as the source of pumped groundwater. The
second well has higher concentrations of MTBE (380 to 973 µg/L) compared to the first well
(39.5 to 180 µg/L). Based on these findings, the city has decreased its usage of the second
well by up to a factor of 4. The well is now only used for 5 to 10 hours per month.
10
Removal of Tikme Exceeding Removal Efficiency (%)
Removal Efficiency (%)
Figure 2.
Removal efficiency reliability at LaCrosse, Kansas.
2.1.4 Technology Cost
A breakdown of expenses for the permanent packed tower air strippers is presented in
Table 4. Capital costs in 1997 were approximately $190,000. Annual O&M costs in the late
1990s were approximately $25,300. However, combined with the cost for remedial actions at
the three gasoline station sites, the total cost of site remediation work exceeded 1 million
dollars as of 2000. This includes the installation and 2-year operation of the pump-and-treat
system, installation of two Oxygen Release Compound (ORC) barriers, source excavations,
and in situ sparging systems in both the source and downgradient areas.
2.2 LOW PROFILE AIR STRIPPER — SOMERSWORTH, NEW HAMPSHIRE
During a routine tank inventory monitoring event in September 1996, a gasoline leak from a
UST was detected at a retail gasoline dispensing facility in Somersworth, New Hampshire.
It was estimated that 2,200 gallons of gasoline had leaked from the tanks, resulting in the
presence of separate-phase hydrocarbons (SPH) in the subsurface and a dissolved-phase
hydrocarbon plume. The site was added to the New Hampshire Department of Environmental Services (NHDES) list of spill response sites on October 4, 1996.
In November 1996, three USTs were replaced. An SVE system, temporary groundwater
extraction, and treatment system were installed. The SVE system was installed to address the
area with free-phase hydrocarbon contamination. The temporary groundwater extraction
11
Table 4. Capital and Annual O&M Costs (1997) for LaCrosse, Kansas
Capital Costs
Towers (x 2)
Building
Concrete pad
Intake screens
Blowers and pumps
Freight
Control panel
Electrical, heating, and lighting
Stripper spare parts (including freight)
Total Capital Costs
Amortized annual costs at 7 percent for 30 years
$119,916
$26,765
$11,142
$3,300
$5,724
$4,384
$2,031
$11,000
$5,706
$189,968
$15,309
Annual O&M Costs
Labor (1 hour/week at $70/hour)
Electricity
Sampling (four/month at $39.25 each)
Monthly reports (12 at $50 each)
Quarterly reports (four at $1,500 each)
Total Annual O&M Costs
$3,640
$13,200
$1,884
$600
$6,000
$25,324
Total annual costs
Amortized Costs/1,000 Gallons
$40,633
$0.57 to 0.76*
*Based on 350- to 480-gpm flow rate and 8-hours/day, 6-days/week operation.
system pumped groundwater from six recovery wells into a 21,000-gallon fractionation tank
through a trailer-mounted oil-water separator. The groundwater was then routed through a
carbon treatment system consisting of four granular activated carbon (GAC) vessels
operating in series. In December 1996, a low profile air stripper and an equalization tank
were installed. The system was set up so that the oil-water separator drained into the 200gallon equalization tank. Water was pumped out of the equalization tank and passed through
the low profile air stripper. The chronology of groundwater treatment and soil remediation at
the site is summarized in Table 5.
Table 5. Timeline for Remediation and Treatment at Somersworth, New Hampshire
Milestone/Event
Date
Gasoline leak detected
September 26, 1996
Temporary treatment system start-up
November 22, 1996
Permanent treatment system start-up
December 10, 1996
Treated effluent ceases discharge to wastewater treatment plant
and begins discharge to stormwater system
August 4, 1999
Treatment system shut-down, due to low concentrations in the influent to the
air stripper and low concentrations in the groundwater monitoring wells
12
May 2000
The air stripper in use at this site is a shallow tray low profile air stripper manufactured by
NEEP. The operating water flow rate ranges from 3 to 10 gpm and the air-to-water ratio is
900 to 1. Influent water quality parameters are presented in Table 6, and design and operating
parameters for the air stripper are presented in Table 7.
Table 6. Average Influent Water Quality Parameters at Somersworth, New Hampshire
Value
Iron (mg/L)
5.6
Effluent temperature (°F)
68
Table 7. Design/Operating Parameters for Low Profile Air Stripper
at Somersworth, New Hampshire
Parameter
Design
Operating
Unit specifications
Four trays
~5-feet wide, 6-feet long, and 6.5-feet high
Configuration
Single low profile air stripper
Blower size (Hp)
7.5
Pump size (Hp)
1.5
160
3 to 10, typically 10
Air flow rate (cfm)
900
900
Air-water ratio
42:1
1,070:1
Maximum MTBE influent concentration (µg/L)
1,670,000
Average MTBE influent concentration (µg/L)
76,700
98.3
The system is operated automatically on a continuous basis. Since treatment started, sampling
has been performed once a month on the combined influent of six recovery wells. The
effluent samples are collected from a sampling port at the base of the air stripper. Samples
are analyzed for purgeable organics (USEPA Methods 8021B and 8260B) and total petroleum
hydrocarbons (USEPA Method 418.1).
Treatment system discharge was initially permitted under an NHDES Temporary Surface
Water Discharge Permit and Temporary National Pollutant Discharge Elimination System
(NPDES) Permit Exclusion. The treated groundwater was initially discharged to the municipal
wastewater treatment facility. Since August 1999, all discharges have been made to the storm
drainage system, which leads to Salmon Falls River.
Air stripper off-gas is directly released into the atmosphere without treatment.
13
Influent concentrations of MTBE have ranged from approximately 200 to 1,000,000 µg/L, as
shown in Figure 3. Removal efficiency typically ranged between 95 to 99 percent, with an
average of 98 percent. The only exception occurred in March 1998, when the removal
efficiency dropped to approximately 70 percent due primarily to silt build-up in the air
stripper. Once the air stripper was cleaned, removal efficiencies improved to previous levels.
Currently, the air stripper requires 16 hours of cleaning every quarter. Measured removal
efficiency of the air stripper is graphically represented in Figures 4 and 5, based on data
shown in Table A-2 of Appendix A.
Figure 4. MTBE removal efficiency at Somersworth, New Hampshire.
14
2/12/2000
12/12/1999
10/12/1999
8/12/1999
6/12/1999
4/12/1999
2/12/1999
12/12/1998
10/12/1998
8/12/1998
6/12/1998
4/12/1998
2/12/1998
12/12/1997
10/12/1997
8/12/1997
6/12/1997
4/12/1997
2/12/1997
12/12/1996
MTBE Removal Efficiency (%)
Figure 3. MTBE concentrations at Somersworth, New Hampshire.
Percentage of Time Exceeding Removal Efficiency (%)
Figure 5.
Removal efficiency reliability at Somersworth, New Hampshire.
The air stripping system has been operating reliably since December 1996. No major repairs
or replacement parts have been needed since system operation began. During operation of
the temporary treatment system (November 22, 1996, to December 9, 1996), a total of
92,400 gallons of groundwater were recovered, treated, and discharged. A status report shows
that 2,566,300 gallons of water had been recovered, treated, and discharged from the start-up
date of December 10, 1996, to February 28, 2000.
The capital cost of air stripper installation totaled $43,000 (1996 dollars). As noted in Table 7,
the system was originally designed to treat 160 gpm. If the operating maximum flowrate of
10 gpm had been anticipated, capital costs would have been even lower. Annual O&M costs
have totaled $15,480 (actual costs during the late 1990s), as shown in Table 8. The total cost
for site remediation and groundwater treatment at this site has exceeded 1 million dollars.
Other approved capital costs in 1996 dollars for various aspects of the remediation project
include recovery well installation and start-up ($81,281), temporary groundwater treatment
system installation ($19,997), permanent treatment system installation ($76,091), and SVE
system installation ($36,017).
2.3 PACKED TOWER AIR STRIPPER — CULVER CITY, CALIFORNIA
Groundwater treatment began in Culver City, California, in November 1999 to address
petroleum hydrocarbons, BTEX, MTBE, and tertiary butyl alcohol (TBA) contamination.
Groundwater is extracted from a total of eight wells screened in two drinking water aquifers.
MTBE was first detected in the wells in late 1995, leading to the closure of the well field in
15
Table 8. Capital and Annual O&M Costs (1996) at Somersworth, New Hampshire
Capital Costs
Low profile air stripper
$20,683
Electrical, heating, and lighting
$16,779
Air stripper installation
$5,460
Total capital costs
$42,923
Amortized annual cost at 7 percent for 30 years
$3,459
Annual O&M Costs
Air stripper cleaning and maintenance
(includes labor for 16 hours quarterly at $70/hour)
$6,480
Electricity (based on $0.12/kWh)
$7,000
Sampling (two/month)
$2,000
$15,480
Total annual costs
$18,939
$22.001
1Based on treatment of 2,566,338 gallons between December 1997 and February 2000.
1997. At the time of data collection, legal investigations and site characterization activities
were being undertaken by the City of Santa Monica, USEPA, and the Los Angeles Region of
the California Regional Water Quality Control Board.
An interim treatment system consisting of packed tower air stripper units was installed to
remove contamination from a LUST at an operating gasoline service station. The extraction
system was designed to provide hydraulic control over movement of the MTBE and BTEX
plumes. The water is currently treated and discharged under an NPDES permit issued by the
Los Angeles Region of the California Regional Water Quality Board. The treatment goal for
MTBE under the NPDES permit is consistent with California’s primary drinking water
standard of 13 µg/L.
The groundwater treatment system consists of multiple unit processes to ensure that the
effluent meets NPDES permit discharge requirements. Groundwater from the wells is
pretreated with approximately 20 mg/L hydrogen peroxide (H2O2) to oxidize ferrous iron to
insoluble ferric iron. A series of three surge tanks is then used to precipitate the iron, followed
by bag filters on the third surge tank to remove any remaining iron oxide particles. The
effluent from the bag filters is treated with a sequestrant solution (20 mg/L of Betz Dearborn
Scaletrol PDC9329) to reduce scaling in the stripper packing. After iron precipitation, the
water is routed through three air strippers in series, each of which can be bypassed, if
necessary, due to cleaning or repairs.
16
The packed tower air strippers, manufactured by Air Chem Systems, Inc., are operated in
series. Each air stripper is 6 feet in diameter, 40 feet in height, and contains 25 feet of No. 2
NUPAC™ polypropylene packing material manufactured by Lantec Products, Inc. Typically,
only two of the three stages are used in series during any given time. Treated water from the
air stripper can undergo ultraviolet (UV) treatment in a 180 kilowatt (kW) medium pressure,
horizontal PeroxPure reactor. H2O2 can be added, if desired, to improve the removal
efficiency of MTBE, TBA, or other organic compounds. Water is also passed through GAC
prior to discharge into a stormwater drain.
Off-gas from the air stripping system is treated using a regenerative thermal oxidizer (RTO)
manufactured by Telkamp Systems, Inc., which has a capacity of 10,000 cfm.
The inorganic parameters measured from samples collected at the air stripper inlet and outlet
in February 2000 are presented in Table 9. The major flow and discharge limitations of the
NPDES permit are summarized in Table 10. The system design and operating parameters for
the air strippers are presented in Table 11, and the influent design parameters are presented
in Table 12.
Table 9. Average Influent Water Quality Parameters at Culver City, California
Parameter
Air Stripper Inlet
Air Stripper Outlet
402
376
Non-detect (<5)
24
Hardness (mg/L as CaCO3)
547
549
Iron (TTLC) (mg/L)
1.4
1.4
Iron (filtered) (mg/L)
2.4
2.5
Manganese (TTLC) (mg/L)
2.4
2.5
pH
6.8
8.5
– 0.3
+1.48
Alkalinity (bicarbonate) (mg/L as CaCO3)
Alkalinity (carbonate) (mg/L as CaCO3)
Langlier Saturation Index
TTLC: Total threshold limit concentration.
MTBE Removal
Water samples are collected at the influent and effluent ports of the treatment system, as well
as at the outlet of each air stripper. MTBE concentrations in the groundwater were reduced
by the air stripping system from up to 17,000 µg/L to less than 2 µg/L (detection limit). The
system has an overall removal efficiency of greater than 99.9 percent. The highest
concentration of MTBE measured in samples collected for the outlet of the first air stripping
column (S-01) was 8.4 µg/L (November 15, 1999). MTBE removal efficiency across the first
air stripper tower ranges between 99.8 and 99.9 percent (most removal occurs in the first air
stripper unit).
17
Table 10. NPDES Permit Limitations at Culver City, California
Parameter
Maximum Value
Discharge rate (gpm)
400
TPH-G (µg/L)
100
Benzene (µg/L)
1
Toluene (µg/L)
150
Ethylbenzene (µg/L)
700
Ethylene dibromide (µg/L)
0.05
Total xylenes (µg/L)
1,750
MTBE (µg/L)
13
TBA (µg/L)
1,750
Sulfides (mg/L)
1.0
Biochemical oxygen demand at 20°C (mg/L)
30
Total suspended solids (mg/L)
50
Settleable solids (mg/L)
0.3
Turbidity (NTU)
150
Temperature (°F)
100
pH
Range from 6.0 to 9.0
NTU: Nepheleometric turbidity unit.
Table 11. Design/Operating Parameters for Packed Tower Air Stripper
at Culver City, California
Parameter
Design
Operating
Tower specifications (x 3)
6-feet diameter x 40-feet tall
Packing
No. 2 NUPACTM packing filled to 25 feet
Configuration
Three towers in series
400
200
Inlet water temperature (°F)
100
70
Air flow rate (cfm)
10,000
7,000
Inlet air temperature (°F)
55 to 85
Air-water ratio
200:1
700:1
Influent normal: 8,000
Influent maximum: 16,000
1st stage: 3,450 to17,000
2nd stage: 8.4
3rd stage: 1.4
Maximum: 35
All stages: Non-detect (<2)
>9
99.9
Table 12. Influent Contaminant Design Criteria at Culver City, California
Constituent
Normal (µg/L)
Maximum (µg/L)
MTBE
8,000
16,000
Benzene
1,000
5,000
Toluene
5,000
10,000
Ethylbenzene
1,000
4,000
Total xylenes
10,000
20,000
Other petroleum hydrocarbons
2,000
4,000
18
Influent MTBE concentrations have decreased steadily since the start-up of the system. In
November 1999, the concentration was 17,000 µg/L. In December 1999 and in March 2000,
MTBE influent concentrations dropped to 7,750 and 3,650 µg/L, respectively. Influent
concentrations measured in April and May 2000 showed MTBE concentrations of 3,300 and
2,900 µg/L, respectively. Influent concentrations over time of MTBE and other gasoline
constituents are presented in Table 13 and Figure 6. Performance data for the three air
strippers are summarized in Table 14 and Figures 7 and 8. Detailed performance data is
contained in Table A-3 of Appendix A.
Table 13. Influent Hydrocarbon Concentrations at Culver City, California
Nov. 1999
(µg/L)
Dec. 1999
(µg/L)
March 20001
(µg/L)
April 20001
(µg/L)
May 20001
(µg/L)
14,000
14,000
10,000
10,000
10,000
Benzene
570
885
510
540
400
Toluene
860
3,500
1,800
1,800
1,500
Ethylbenzene
340
615
330
340
380
Xylenes
1,660
3,600
2,200
2,400
2,100
MTBE
17,000
7,750
2,800
3,300
2,900
TBA
3,500
1,200
570
330
260
Constituent
TPH-G
MTBE Concentration (mg/L)
1Influent concentration based on two to three sets of analytical results provided by two different analytical laboratories.
Data Point ID
Figure 6.
MTBE concentrations at Culver City, California.
19
Table 14. Air Stripper Performance Data for MTBE at Culver City, California
Date
Influent (µg/L)
S-01 (µg/L)
S-02 (µg/L)
S-03 (µg/L)
Effluent (µg/L)
11/10/99
17,000
NA
NA
NA
ND (<1)
11/15/99
3,818
8.4
1.4
1.4
NA
12/20/99
6,300
NA
NA
NA
ND (<1)
12/21/99
2,400
NA
NA
ND (<1)
NA
01/13/00
4,500
NA
NA
NA
ND (<1)
01/21/00
5,100
1.3
ND (<1)
1.1
NA
02/01/00
4,200
1.1
Offline
1.0
ND (<1)
02/12/00
3,000
ND (<1)
Offline
ND (<1)
ND (<1)
02/16/00
3,200
1.3
Offline
1.5
ND (<1)
02/25/00
3,000
ND (<1)
Offline
ND (<1)
ND (<1)
1
03/01/00
2,500
ND (<1)
Offline
ND (<1)
ND (<1)
03/09/00
2,900
ND (<1)
Offline
ND (<1)
ND (<1)
03/15/00
4,100
ND (<1)
Offline
ND (<1)
ND (<1)
1
3,300
NA
Offline
ND (<1)
ND (<5)
1
2,900
NA
Offline
ND (<1)
ND (<5)
04/04/00
05/09/00
1Influent concentrations based on two to three sets of analytical results provided by two different analytical laboratories.
NA: Not available.
ND: Non-detect.
Trial #
Figure 7.
MTBE removal efficiency at Culver City, California.
20
Figure 8.
Air stripping performance at Culver City, California.
Total Petroleum Hydrocarbon Quantified as Gasoline (TPH-G)/BTEX Removal
The air stripping system removed total petroleum hydrocarbon quantified as gasoline (TPH-G)/
BTEX from groundwater to below laboratory detection limits (approximately 1 µg/L), with
an overall removal efficiency equal to or greater than 99.9 percent. Moreover, all effluent
samples from the first stripping column had non-detectable levels of TPH-G/BTEX,
suggesting that TPH-G/BTEX removal essentially occurred in the first stripping column.
TBA Removal
Average monthly influent concentrations of TBA ranged from 260 to 3,500 µg/L between
November 1999 to May 2000. During this period, TBA removal efficiency in the air stripping
system increased from approximately 74 percent to greater than 90 percent. Most of the TBA
removal occurred in the first air stripping column. The improvement in TBA removal
efficiency over time is potentially due to the development of a microbial community on the
surfaces of the air stripper packing that is capable of TBA degradation.
The only apparent problem with air stripper operation was the build-up of scale in the pretreatment system. The system operates continuously. Between its start-up date of November 12,
1999, and March 15, 2000, this system treated 11,537,000 gallons of water. Based on this
data, the flow rate of treated water is approximately 67 gpm. From March to May 2000,
groundwater extraction rates were approximately 64 to 66 gpm.
21
The capital cost of the entire system (including pretreatment, the three air strippers, off-gas
treatment, and GAC polishing) was approximately $1,714,000. Annual operating costs
(including electricity, GAC, chemicals, labor, and supplies) are estimated to be $360,000. A
breakdown of these costs is presented in Table 15. These costs are based on June 1998
estimates; actual costs may be higher or lower.
Table 15. Capital and Annual O&M Costs (1999) at Culver City, California
Capital Costs
Pretreatment system, air strippers, off-gas treatment, and GAC polishing
$1,714,000
Total capital costs
$1,714,000
Amortized annual cost at 7 percent for 30 years
$138,125
Annual O&M Costs
Utility costs (electrical power and natural gas)
$145,000
Granular activated carbon
$20,000
Chemical costs (catalyst and scale control)
$67,000
General O&M (labor and miscellaneous supplies)
$127,000
$359,000
Total annual costs
$497,125
1
Amortized Costs/1000 Gallons
$14.50
1Based on a calculated treated groundwater flow rate of 94,000 gallons per day at continuous operation.
2.4 LOW PROFILE AIR STRIPPER — BRIDGEPORT, CONNECTICUT
In April 1995, groundwater treatment was installed to remediate a site impacted by a gasoline
spill from a product terminal in Bridgeport, Connecticut. The system produced such consistently
low MTBE concentrations that it ceased operation sometime in 1998.
A heat exchanger was used to increase the temperature of the water from 55°F to
approximately 65°F as a pretreatment step. After heating, the water enters the shallow tray
low profile air stripping units, which are arranged in two parallel trains of two units. The air
strippers are manufactured by Ejector Systems, Inc. (Model LP-5005). Water exiting the air
strippers is further treated using GAC and sand dual media filtration. The water flow rate is
approximately 11 gpm and the gas flow rate is approximately 500 standard cubic feet per
minute (scfm), resulting in an air-to-water ratio of 340 to 1. The influent water quality
parameters at the site are presented in Table 16. Design and operating parameters for the air
stripping treatment system are summarized in Table 17.
22
Table 16. Average Influent Water Quality Parameters at Bridgeport, Connecticut
Concentration
Calcium (mg/L)
61
Iron (mg/L)
21
Manganese (mg/L)
5.2
Phosphate (mg/L)
0.2
Inlet pH
6.6
Temperature (°F)
55 to 65
Table 17. Design/Operating Parameters for Low Profile Air Stripper
at Bridgeport, Connecticut
Parameter
Design
Operating
Unit specifications (x 4)
Low profile air stripper
Configuration
Two parallel systems of two in series
20
11
Gas flow rate (cfm)
1,000
500
Air-water ratio
375:1
340:1
Maximum influent MTBE concentration (µg/L)
Primary AS: 2,400,000
Secondary AS: 14,000
Maximum influent BTEX concentration (µg/L)
Primary AS: 34,000
Secondary AS: 70
50
99.9
AS: Air stripper.
The off-gas released from the primary air stripper is treated with a catalytic oxidizer.
Off-gases released from the secondary air stripper are directly exhausted to the atmosphere.
Initially, concentrations of MTBE entering the primary air stripper unit ranged from 280,000
to 2,400,000 µg/L. Concentrations entering the secondary air stripper unit ranged from 100
to 14,000 µg/L. Treated effluent MTBE concentrations ranged from 50 to 200 µg/L. Samples
were collected on a monthly basis for a period of 1 year following the start-up of the
treatment system, but regular sampling was discontinued soon after due to very low MTBE
levels. By 1998, MTBE concentrations were low enough (i.e., 50 to 200 µg/L) for treatment
system operation to cease. Influent and effluent data for MTBE and BTEX are presented in
Tables 18 and 19, respectively. Influent and effluent MTBE data are represented in Figure 9.
Removal efficiencies and performance data for the air stripper are illustrated in Figures 10a,
10b, and 11. All figures were generated using the detailed performance data shown in
Tables A-4a and 4b of Appendix A.
23
Table 18. Air Stripper Performance Data for MTBE at Bridgeport, Connecticut
Influent
(µg/L)
Primary Stripper Effluent
(µg/L)
Secondary Stripper
Effluent (µg/L)
April 1995
2,400,000
3,100
<50
May 1995
1,100,000
14,000
<50
June 1995
1,100,000
2,700
<50
July 1995
960,000
1,100
<50
August 1995
630,000
90
<50
September 1995
360,000
150
<50
October 1995
490,000
160
<50
November 1995
480,000
250
<50
December 1995
480,000
3,500
100
February 1996
580,000
1,400
<50
March 1996
200,000
6,600
200
Date
Table 19. Air Stripper Performance Data for BTEX Compounds at Bridgeport, Connecticut
Influent (µg/L)
Primary Stripper Effluent
(µg/L)
Secondary Stripper
Effluent (µg/L)
April 1995
34,000
50
<10
Mary 1995
14,600
<10
<10
June 1995
26,900
60
20
July 1995
22.600
70
20
August 1995
18,500
30
20
September 1995
11,000
<10
<10
October 1995
21,000
<10
<10
November 1995
15,900
<10
<10
December 1995
19,300
30
<10
February 1996
16,500
<10
<10
March 1996
15,100
30
<10
Date
24
MTBE Concentration (mg/L)
Figure 9.
MTBE concentrations at Bridgeport, Connecticut.
Through S1
Through S2
Through S1 & S2
Figure 10a.
MTBE removal efficiency at Bridgeport, Connecticut.
25
Through S1
Through S2
Through S1 & S2
Percentage of Time Exceeding Removal Efficiency (%)
Figure 10b.
BTEX removal efficiency at Bridgeport, Connecticut.
Figure 11.
Removal efficiency reliability at Bridgeport, Connecticut.
26
The capital cost of the system was approximately $530,000 (1995 dollars). Annual O&M
costs were approximately $48,000 during the mid-1990s. A breakdown of these costs for
removing MTBE from groundwater is presented in Table 20.
Table 20. Capital and Annual O&M Costs (1995) at Bridgeport, Connecticut
Capital Costs
Towers (x 4)
$132,500
Total Capital Costs
$530,000
$42,711
Annual O&M Costs
Operating costs not related to MTBE treatment
$84,000
Power requirement
$6,000
Labor
$5,760
Parts replacement
$8,100
Air stripper cleaning
$5,220
System oversight
$6,000
$48,000
Total annual costs
$90,711
$15.701
1Based on an 11-gpm flow rate with continuous operation.
2.5 LOW PROFILE AIR STRIPPER — CHESTER, NEW JERSEY
In 1998, a low profile air stripper was installed at a site in Chester, New Jersey, to remove
MTBE from a domestic well. The well water is pumped on an as-needed basis at 50 gpm.
The treated water is stored prior to its use and then pumped at 15 gpm through the
distribution system. The treatment system had been operating for over 18 months at the time
of data collection for this report.
Prior to air stripping, extracted groundwater is passed through a two-step pretreatment
system consisting of acid neutralization and water softening. Following pretreatment, the
well water is routed to a four-tray shallow tray low profile air stripper manufactured by NEEP
(Model #2341-P). The well water is then polished using GAC and chlorinated prior to use.
27
Influent water quality parameters of the extracted groundwater are shown in Table 21. Design
and operating data for the air stripping system are presented in Table 22. Since the start-up
of the system, no problems have been encountered and no parts have been replaced. System
maintenance (i.e., cleaning and inspection) is performed on a semi-annual basis.
The off-gas from the air stripper is directly exhausted to the atmosphere without prior
treatment.
Table 21. Average Influent Water Quality Parameters at Chester, New Jersey
Concentration
257
pH
6.1
Temperature range (°F)
40 to 45
Table 22. Design/Operating Parameters for Low Profile Air Stripper at Chester, New Jersey
Parameter
Design
Operating
Unit specifications
Four trays
~5-feet wide, 3.5-feet long, and 6.5-feet high
Configuration
Single low profile air stripper
1 to 50
15
Air flow rate (cfm)
300
150
Air-water ratio
45:1
75:1
Not available
220
Maximum MTBE influent concentration (µg/L)
MTBE effluent concentration (µg/L)
14
Other contaminants
TCE
941
1Includes post-treatment GAC polishing step performance.
TCE: Trichloroethylene.
Trichloroethylene (TCE) was detected in the well water at the beginning of system start-up.
However, the treatment system has successfully reduced TCE to non-detectable levels.
MTBE concentrations were reduced from up to 220 µg/L in the influent groundwater to
concentrations as low as 14 µg/L after the GAC polish, giving an average MTBE removal
efficiency of 94 percent for the entire system. Unfortunately, the effluent MTBE
concentration out of the air stripper was not measured. Removal efficiency is less than or
equal to 94 percent for the air stripper units.
28
The capital cost for installing the air stripper was $15,000 (1998 dollars), and an annual
amount of $4,460 is needed for O&M. A detailed description of the costs related to the
treatment system is presented in Table 23.
Table 23. Capital and Annual O&M Costs (1998) at Chester, New Jersey
Capital Costs
Total Capital Costs
$15,000
$1,209
Annual O&M Costs
Power requirements
$3,267
Chemical addition (chlorine)
$75
Labor (16 hours/year at $70/hour)
$1,120
$4,462
Total annual costs
$5,671
$1.401
1Calculation based on 15-gpm flow rate and operation for periods of 12 hours/day, 7 days/week.
2.6 PACKED TOWER AIR STRIPPERS — RIDGEWOOD, NEW JERSEY
The treatment facility in Ridgewood, New Jersey, is an air stripping facility designed to
remove VOCs from two municipal wells. The facility was originally designed to treat up to
635 gpm, although only 525 gpm is currently being pumped from the wells, which operate
75 percent of the time.
The treatment facility was originally constructed in 1991 and consisted of a single air
stripping tower designed to remove 99 percent of perchloroethylene (PCE) in the blended
influent. Several influent water quality parameters for the blended groundwater supply are
summarized in Table 24. Raw water from the two wells was pumped through the air stripper
and into a clear well where chlorine was added for disinfection. From the clear well, the
treated water was pumped into the municipal distribution system. In 1997, a second air
Table 24. Average Influent Water Quality Parameters at Ridgewood, New Jersey
Temperature (°F)
50 to 55
pH
7.7
Alkalinity (mg/L as CaCO3)
160 to 170
200 to 250
29
stripping tower was added to the facility in response to the detection of MTBE in one of the
wells. The facility was reconfigured such that the new air stripping tower (AST-2) was
dedicated to treating water from the well containing MTBE, while the original air stripping
tower (AST-1) was dedicated to the well without MTBE. The treated water from both air
stripping towers was discharged into the clear well, after which the water was disinfected and
distributed. The facility has continued to operate in this configuration.
As mentioned, AST-1 was originally designed to remove 99 percent of the PCE in the blended
influent from the two wells. The design information for AST-1 is presented in Table 25.
AST-2 was added in 1997 and designed to reduce MTBE concentrations in the influent from
689 to 15 µg/L (97.8 percent removal). This concentration was selected as a target concentration since it is close to MTBE’s taste and odor threshold. The new air stripping tower has the
Table 25. Design/Operating Parameters for Packed Tower Air Stripper
at Ridgewood, New Jersey
AST-1
Parameter
Design
AST-2
Operating
1
Design
Operating
1
Manufacturer
Hydro Group, Inc.
Hydro Group, Inc.
Model number
PCS-69.23
PCS-69.23
Year installed
1991
1997
2
Shell material
Aluminum
Aluminum with interior coating
Tower diameter (feet)
5.75
5.75
Packed bed depth (feet)
23
23
Packing media
2-inch Tri-Packs3
2-inch Tri-Packs
Other contaminants
PCE
PCE
Maximum influent MTBE
concentration (µg/L)
689
Average influent MTBE
90
Effluent MTBE
15 (goal);
70 (standard)
15
Percent removal (%)
97.8
83.3
635
300
225
225
Liquid loading rate (gpm/sf)
24.6
11.6
8.7
8.7
Air flow rate (cfm)
4,280
4,280
7,500
7,500
Air-water ratio
50:1
110:1
250:1
250:1
Number of air blowers
1
1
Blower motor size (Hp)
5
10
1Now Layne Christensen Company, Bridgewater, New Jersey.
2Tower shell interior coated with epoxy in 1997.
3Jaeger Products, Inc., Houston, Texas.
30
same physical dimensions as AST-1, but was designed to handle a lower liquid loading rate
at a higher air-to-water ratio than AST-1 (see Table 25).
With the addition of AST-2, the operating parameters of AST-1 were modified because this
air stripper was now treating only one well. Neither AST-1 nor AST-2 required off-gas
treatment systems. A summary of the current operating configurations for both towers is
provided in Table 25.
Following the installation of AST-2, MTBE was no longer detected in the raw well water. The
treatment system continued operating to remove PCE. The only information available
regarding MTBE removal rates at this facility is from system performance reports
immediately prior to the installation of AST-2. For the first few months following the
detection of MTBE, the original system was successful in reducing MTBE concentrations in
the water to levels below New Jersey’s maximum contaminant level (MCL) of 70 µg/L
MTBE. At that time, the concentration of MTBE in the blended raw water from the two wells
averaged approximately 90 µg/L. With AST-1 operating at a liquid loading rate of
20 gpm/square feet (sf) and an air-to-water ratio of 60 to 1, approximately 30 percent MTBE
removal was achieved.
Although no operating data is available to confirm satisfactory operation of the air stripping
tower that was specifically designed to remove MTBE (AST-2), this case study illustrates that
the original air stripper, which was not designed for MTBE removal, was able to achieve
some reduction in MTBE.
The construction cost of the original air stripping system (AST-1) in 1991 was approximately
$450,000 (which includes the air stripper, blower, piping, and controls, in addition to a
concrete clear well, booster pumps, and a building to house the pumps, blowers, and controls).
The cost associated with the addition of AST-2 in 1997 was approximately $200,000 (which
includes the purchase of a new tower, blower, piping, and controls). This accounts for the
construction costs associated with the extension of the existing building to house the new
blower, in addition to the cost associated with an internal epoxy coating for the original air
stripper (AST-1). Thus, the total capital cost of the facility is approximately $770,000. The
O&M costs associated with the facility are approximately $72,000 per year. A breakdown of
all the costs is presented in Table 26.
31
Table 26. Capital and Annual O&M Costs (1991, 1997) at Ridgewood, New Jersey
Capital Costs
Installation of AST-1
(Includes tower, blower, piping, controls, concrete clear well, booster pumps and
building to house tower, blower, and controls)
$450,000
Installation of AST-2
(Includes tower, blower, piping, controls, and building expansion)
$200,000
Total Capital Costs1
$770,000
$62,050
Annual O&M Costs
Power requirements (unit cost of $0.12 kWh)
$53,000
Sampling
$5,000
Labor (5 hours/week at $40/hour)
$11,000
Miscellaneous expenses
$3,000
$72,000
Total annual costs1
$134,000
$0.642
1Cost is based on year 2000 values.
2Based on a 525-gpm flow rate and 75 percent of the time operation.
2.7 PACKED TOWER AIR STRIPPER — ROCKAWAY TOWNSHIP, NEW JERSEY
A packed tower air stripper was installed in 1982 to treat volatile organic contaminants,
including TCE, PCE, trans-1,2-dichloroethylene (DCE), di-isopropyl ether (DIPE), and
MTBE, in the groundwater supply for Rockaway, New Jersey. The air stripper was originally
a pretreatment step for GAC, but replaced GAC in 1983 as raw water DIPE and MTBE
concentrations declined. The GAC system was maintained in operable condition to serve as
a backup for the air stripper.
This mode of operation continued until 1995, when the original air stripper was replaced with
a new one. The new air stripping tower was not designed to remove DIPE and MTBE because
their concentrations were declining over time. Within approximately 2 years of tower replacement, though, a second accidental UST release occurred, causing MTBE to appear once
again in the supply wells. Since the MTBE levels resulting from the second release were
relatively low (approximately 5 to 10 µg/L), the Township was able to modify the existing air
stripping tower to provide adequate treatment. The modified system configuration is still
maintained and has been effective in producing treated water with MTBE levels below
1 µg/L.
32
1982 Treatment System
The air stripping tower installed in 1982 was manufactured by Layne (currently known as
Layne Christensen Company of Bridgewater, New Jersey). It was one of the first air stripping
systems in the United States designed for VOC removal from municipal water supplies. To
determine the design criteria for the air stripper, a series of pilot-scale tests was conducted at
the Township’s well site. Based on these tests, the air stripping tower was designed to achieve
99.9-percent removal of DIPE, which was determined to be primarily responsible for taste
and odor problems. The design parameters of the 1982 air stripping tower are summarized in
Table 27. The treated water was stored in a clear well followed by either polishing with GAC
and chlorine disinfection or chlorine disinfection and direct routing into the distribution
system. No off-gas treatment was required for this system.
Table 27. Design/Operating Parameters for Packed Air Stripping Tower
at Rockaway Township, New Jersey
1982 Tower
Operating
1995 Tower
Parameter
Design
Design
Operating
Manufacturer
Layne
Remedial Systems, Inc.
Shell material
Aluminum
Fiberglass Reinforced Plastic
Tower diameter (feet)
9
9
Packed bed depth (feet)
25
25
1
Packing media
3-inch Tellerettes
3.5-inch LanPacs2
Other contaminants
TCE, PCE, trans-1,2-DCE, DIPE
TCE, PCE, trans-1,2-DCE
Maximum MTBE influent
60
Effluent MTBE
<1
5 to 10
<1
<1
95
65
1,400
1,500
Liquid loading rate (gpm/sf)
22
23.6
Air flow rate (cfm)
37,500
20,000
Air-water ratio
100:1
100:1
Number of air blowers
2
1
Blower motor size (Hp)
100
30
1Ceilcote Co., Beria, Ohio.
2Lantec Products, Inc., Agoura Hills, California.
DCE: Dichloroethylene.
DIPE: Di-isopropyl ether.
33
35
The replacement air stripping tower that was brought online in 1995 was manufactured by
Remedial Systems, Inc., and was designed to meet VOC removal criteria (Table 28). The
expected influent concentration for MTBE was relatively low. As a result, MTBE did not
govern the air stripping tower design. By 1995, detections of MTBE and DIPE had ceased in
the Township’s water supply. From the criteria listed in Table 28, it is clear that the most
stringent requirement was the 99.9-percent removal of TCE that was still present in the
Township’s groundwater supply. The design parameters for the second air stripping tower to
meet these criteria are summarized in Table 27. The significant difference between the airto-water ratios for the original and replacement air stripping towers is primarily due to the
fact that TCE has a much higher Henry’s Law constant than MTBE and, therefore, is easier
to remove from water. The design specifications for the replacement system were developed
without the benefit of a pilot study. This was possible since the design of air stripping towers
for removal of common VOCs, such as TCE, had become fairly routine by 1995 and
sufficient operating data was available to use for this design.
Table 28. VOC Criteria for 1995 Air Stripping Tower at Rockaway Township, New Jersey
Compound
Design Influent
Concentration (µg/L)
Design Effluent
Concentration (µg/L)
Design Removal
Efficiency (%)
Chloroform
10
1
90
cis-1,2-dichlorethylene
15
5
67
1,1-dicholorethane
10
1
90
1,1-dichlorethylene
10
1
90
MTBE
5
1
80
PCE
5
0.5
90
1,1,1-trichlorethane
30
10
67
TCE
500
0.5
99.9
5
0.5
90
Carbon tetrachloride
In 1997, MTBE was again detected in the Township’s water supply. The Township responded by
replacing the existing 30 horsepower (Hp) blower motor with a new 35 Hp motor to increase
air flow through the air stripping tower. This modification resulted in an air flow increase of
approximately 200 cfm, which did not significantly affect the design air-to-water ratio.
Although sampling data are not available for analysis in this report, the air stripping tower
consistently achieved 95-percent removal of MTBE during the first 12 months of operation
(February 1982 to February 1983). Influent MTBE concentrations during this period ranged
from 50 to 60 µg/L and, thereafter, decreased to below 10 µg/L. Since the detection limit for
34
MTBE is 0.5 µg/L, analyzing the air stripping tower performance after February 1983
became difficult. The only measure of performance from 1983 to 1995 is that the air
stripping tower operating alone was able to eliminate taste and odor problems in the
Township’s drinking water supply.
A summary of representative influent water quality parameters is provided in Table 29. As
shown in Figure 12 and Table A-5 of Appendix A, the concentration of MTBE in the
combined raw influent ranged from non-detect (less than 0.5 µg/L) to 11.4 µg/L. During this
same 30-month time period, the maximum MTBE concentration in the air stripping tower
effluent was 2.0 µg/L. Furthermore, MTBE was non-detect in 47 of the 69 samples collected.
Table 29. Average Influent Water Quality Parameters at Rockaway Township, New Jersey
Value
Temperature (°F)
50 to 55
Total dissolved solids (mg/L)
374
Manganese (mg/L)
0.01
Iron (mg/L)
0.05
Hardness as CaCO3 (mg/L)
217
pH
7.37
– 0.28–
MTBE Concentration (ppb)
Corrosivity
Sample Date
Figure 12.
MTBE concentrations versus time at Rockaway, New Jersey.
35
MTBE Removal Efficiency
Although the low influent MTBE levels make it difficult to analyze the performance of this
air stripping tower, it was possible to draw some conclusions from the data where MTBE was
detected in the effluent. Figure 13 shows that while the air stripping tower performance
varied widely over the period of operation, the average MTBE removal efficiency was
approximately 65 percent. Figure 14, which depicts the performance reliability curve for this
system, indicates that this tower removed 80 percent of MTBE approximately 45 percent of
the time. However, the system was operating at low MTBE influent concentrations, which
Sampling Date
Percentage of Time Exceeding Removal Efficiency
Figure 13.
MTBE removal efficiency versus time at Rockaway, New Jersey
Removal Efficiency
Figure 14.
Removal efficiency reliability at Rockaway, New Jersey.
36
may have resulted in reduced removal efficiency. Although percent MTBE removal was low,
the data available for the 1995 air stripping tower indicate that this system is capable of
achieving a moderate degree of MTBE removal, even though it was not specifically designed
for this VOC.
The total construction cost of the air stripping system in 1982 was approximately $375,000.
Using historical Consumer Price Index values published by the U.S. Department of Labor,
this equates to $645,750 in year 2000 dollars. While this cost may seem excessive in
comparison to modern air stripping systems, the cost should be considered in the context of
the time: a limited number of manufacturers were available in 1982 and experience with
full-scale construction was limited.
The estimated annual O&M costs associated with the air stripping tower were approximately
$160,000 (in year 2000 dollars). These costs include power ($135,000),1 sampling ($11,000),
labor ($11,000),2 and an allowance for other miscellaneous repairs and replacement parts
($3,000).
A breakdown of costs for the 1995 treatment system is shown in Table 30. The construction
cost associated with the replacement air stripping tower in 1995 was approximately
$300,000, which included the costs for a new tower, clear well, air blower, piping, and a small
building to house the blowers and booster pumps. This cost also included the demolition of
the existing tower and blower, as well as the relocation of existing booster pumps. To develop
a representative cost estimate for the air stripping system that is currently in operation at
Rockaway Township, the following assumptions were made:
• First, an allowance for the demolition of the existing equipment was deducted from the
construction cost given above since this would not be typically required for the construction
of a new air stripping tower.
• Second, the cost associated with the two booster pumps was added to the construction cost
since these units would typically be installed as part of the air stripping system.
• Finally, the cost of upgrading the blower motor in 1997 was added to the total cost.
The net result, scaled to reflect year 2000 dollars, led to an estimated construction cost of
$370,000.
1 Based on a unit cost of $0.12/kilowatt hour (kwh).
2 Based on 5 hours per week at $40/hour (including fringe benefits).
37
Table 30. Capital and Annual O&M Costs (1995, 2000) at Rockaway Township, New Jersey
Capital Costs
Installation of current air stripping operation in 1995 (Includes tower, blower,
piping, controls, clear well, booster pumps, and building to house tower, blower,
booster pumps, and controls)
$300,000
$370,000
$29,800
Annual O&M Costs
Power requirements (unit cost of $0.12/kWh)
$95,000
Sampling
$11,000
Labor (5 hours/week at $40/hour)
$11,000
Miscellaneous expenses
$3,000
Total Annual O&M Costs1
$120,000
Total annual costs
$150,000
2
$0.22
1Cost is based on year 2000 values.
2Based on a 1,300-gpm flow rate and continuous operation.
The estimated annual O&M costs associated with the replacement air stripping tower are
approximately $120,000 in year 2000 dollars. These costs include power ($95,000),3
sampling ($11,000), labor ($11,000),4 and an allowance for other miscellaneous repairs and
replacement parts ($3,000). Note that the power costs for the replacement system are
significantly lower due to the fact that the two original 100 Hp blower motors have been
replaced with a single 35 Hp unit.
2.8 LOW PROFILE AIR STRIPPER — MAMMOTH LAKES, CALIFORNIA
In 1999, a fuel leak in a UST was detected in Mammoth Lakes, California. Concentrations
of MTBE measured in six groundwater monitoring wells in the vicinity of the leak ranged
from non-detect (less than 5 µg/L) to as high as 463,000 µg/L. An interim groundwater
treatment system was installed and used from January 2000 until March 2000. During this
interim period, treated water was stored onsite in a 21,000-gallon storage tank. The full-scale
treatment system was officially started in March 2000. Treated groundwater is now
discharged to Dry Creek in accordance with an NPDES permit. An SVE system has also
been installed at the site. Organic vapors that are extracted from the subsurface are destroyed
using a catalytic/thermal oxidation unit. A timeline of events at the site is presented in Table 31.
3 Based on a unit cost of $0.12/kwh.
4 Based on 5 hours per week at $40/hour (including fringe benefits).
38
Table 31. Timeline of Events at Mammoth Lakes, California
Milestone/Event
Date
Vapor extraction system change-over from 250 to 350 cfm thermal
oxidizer unit
January 13, 2000
Treatment system start-up and testing
February 29, 2000
Treatment system begins discharge to Dry Creek
March 10, 2000
Vapor extraction system unit shut down and maintenance
May 24, 2000
Vapor extraction system restarted
June 16, 2000
Four extraction wells are used to contain the groundwater plume. The system flow rate varies
from approximately 2 to 15.5 gpm and averages 6.5 gpm. The water is heated and passed
through two biologically activated GAC vessels to reduce concentrations of total nitrogen,
total phosphorus, and bacteria prior to treatment with a shallow tray low profile air stripper.
A liquid-phase GAC treats air stripper effluent prior to collection in a 21,000 gallon tank and
discharge to Dry Creek. Influent concentrations for a number of constituents in the
groundwater are shown in Table 32. Since the system start-up through June 2000, a total of
1,016,000 gallons of water have been treated.
Table 32. Influent Constituent Concentrations for at Mammoth Lakes, California
Constituent
Influent Concentrations (µg/L)
TPH-G
2,000 to 940,000
MTBE
660 to 97,000
Benzene
62 to 1,500
Air stripper off-gas is treated using two vapor-phase GAC vessels prior to discharge to the
atmosphere. The flow rate of air through this treatment system is approximately 2,400 cfm.
MTBE effluent concentrations through the air stripper and the entire system can be found in
Table 33. Removal efficiencies are greater than 99.9 percent through the air stripper. Off-gas
treatment concentrations can be found in Table 34. Off-gas treatment removal efficiencies
range from 93 to 99.7 percent.
No cost data was readily available for this site.
39
Table 33. MTBE Air Stripping Performance Data at Mammoth Lakes, California
Date
Influent (µg/L)
Air Stripper Effluent (µg/L)
Discharge Effluent (µg/L)
02/29/00
4,100
1.7
<0.5
03/01/00
4,000
0.6
<0.5
03/10/00
5,300
2.1
<0.5
03/11/00
6,200
NA
NA
03/13/00
660
<0.5
<0.5
03/16/00
900
0.6
<0.5
03/22/00
5,800
<0.5
NA
03/29/00
5,400
NA
NA
04/05/00
12,000
NA
NA
04/12/00
8,500
NA
NA
04/19/00
12,492
<0.5
<0.5
04/26/00
38,000
NA
NA
05/04/00
35,000
NA
<0.5
05/10/00
35,000
NA
NA
05/16/00
18,000
NA
NA
05/24/00
8,600
1
<0.5
06/01/00
15,000
1
<0.5
06/14/00
9,900
2
<0.5
NA: Not analyzed.
Table 34. MTBE Off-Gas Treatment Performance Data at Mammoth Lakes, California
Date
MTBE
Influent Off-Gas
(ppmv)
MTBE
Effluent Off-Gas
after First GAC Vessel
(ppmv)
MTBE
Effluent Off-Gas
after Second GAC Vessel
(ppmv)
03/13/00
0.015
0.002
<0.001
06/01/00
0.59
0.001
0.002
06/14/00
0.34
0.002
<0.001
2.9 LOW PROFILE AIR STRIPPER — ELMIRA, CALIFORNIA
In 1997, the remediation of a petroleum pipeline leak in Elmira, California, began with the
installation of two extraction and treatment systems. A timeline of the site remediation events
is included in Table 35. One of the systems included a low profile air stripping unit and
adsorption off-gas treatment system. The air stripping system performance data and background information at the site were limited. However, performance information was available
for the off-gas treatment system.
40
Table 35. Timeline of Remediation at Elmira, California
Milestone/Event
Date
Residents in Elmira, California, begin complaining about petroleum odors. Petroleum
leak is discovered. Saturation of soil in the area of municipal sewer is detected.
Prior to 1997
Installation of extraction and treatment system (air stripper, liquid-phase GAC vessels in
series, and vapor-phase GAC).
Installation of new off-gas treatment system (ADDOXTM).
1997
February 2000
Groundwater is extracted at an average rate of 25 gpm and passed through a treatment train
consisting of the following: an oil/water separator, bag filter, solar heating array, low profile
air stripper, and two liquid-phase GAC vessels operating in series. Anti-scalant, biogrowth
control, and anti-foaming chemicals are added prior to the air stripper. The solar heating step
improves air stripper efficiency. Influent water quality parameters at this site are listed in
Table 36. Design parameters for the air stripping system are included in Table 37a.
Table 36. Average Influent Water Quality Parameters at Elmira, California
Value
Alkalinity as CaCO3 (mg/L)
250 to 350
pH (estimated average)
7.5
Total organic carbon (estimated average) (ppm)
3.6
Temperature (average) (°F)
62
Table 37a. Design/Operating Parameters for the Low Profile Air Stripper at Elmira, California
Parameter
Design
Operating
Low Profile stripper specifications
4-foot, 2-inch wide x 6-foot, 2-inch long x 6-foot, 8-inch tall
Four trays
Configuration
One air stripper
Blower size
15 Hp, originally
10 Hp blower added at inlet for off-gas treatment
30 to 60 gpm
115 gpm
25 (average)
30 (maximum)
Air flow rate (cfm)
600
300 (average)
525 (maximum)
Air-water ratio
39
90
210,000
NA
Maximum BTEX concentration (µg/L)
9,800
NA
13 (required)
1 (design)
NA
>99.9
NA
NA: Not available.
41
One air stripper
The low profile air stripper is manufactured by NEEP. The system has operated continuously
with the exception of brief shutdown periods for scheduled and unscheduled maintenance
and carbon changeouts. The system had been operating for approximately 3 years at the time
of data collection for this report. Approximately 23,300,000 gallons had been treated as of
July 2000. Samples are collected monthly at the air stripper influent and GAC effluent and
are analyzed for total petroleum hydrocarbon (gas and diesel range), BTEX, MTBE, DIPE,
TBA, ethyl tertiary butyl ether (ETBE), and tertiary-amyl methyl ether (TAME).
Vapor-phase GAC vessels were originally installed to treat the air stripper off-gas. These
were in use for approximately 3 years. In February 2000, a new off-gas treatment system
called ADDOXTM (Model ADDOX6), manufactured by NEEP, was installed to provide more
cost-effective off-gas treatment. GAC vessels remained at the site on standby. The ADDOXTM
system had been in operation for several months at the time of data collection for this report.
This unit remains under a “testing phase” by NEEP to assess the degree of O&M required
by the system. An ADDOXTM system consists of two or more reaction chambers filled with
an inorganic, non-combustible media. At least one chamber adsorbs, while the other desorbs,
destroys, and regenerates. VOC-laden air enters the adsorbing chamber and the contaminants
are captured on the adsorbent beds; clean air is then allowed to exit the chamber. The
contaminants are released from the bed when a stream of clean, preheated air is blown into
the chamber during the regeneration phase. The VOCs are oxidized into carbon dioxide and
water through an exothermic catalytic oxidation reaction. The heat from the reaction
increases VOC desorption from the media. According to a NEEP ADDOXTM system vendor,
the adsorption/desorption cycle is every 4 hours for the system operating at this site.
The system is designed to treat a maximum air flow rate of 600 scfm and a maximum VOC
adsorption and destruction rate of 4.4 pounds per hour. The system is 11.5 feet long, 7.5 feet
wide, and 9 feet tall, and designed to treat an off-gas stream containing total VOC
concentrations of 255 parts per million by volume (ppmv), of which 151 ppmv is MTBE.
Design parameters for the off-gas treatment system are included in Table 37b.
Table 37b. Design/Operating Parameters for the Off-Gas Treatment System (ADDOXTM)
at Elmira, California
Parameter
Design
Specifications
7-feet, 6-inches wide x 11-feet, 6-inches long x 9-feet tall
Configuration
Two inorganic media beds alternating between adsorption and
desorption/regeneration phases
Blower size (Hp)
2
Air flow rate (cfm)
600 for adsorption,
60 for desorption
600 for adsorption,
60 for desorption
Maximum MTBE concentration (ppmv)
500
393
Maximum BTEX concentration (ppmv)
6.6
NA
MTBE treatment goal (ppmv)
<3
NA
>98
>99
NA: Not available.
42
Operating
Influent MTBE concentrations range from 1,700 to 100,000 µg/L. The final effluent from the
system has consistently met NPDES discharge requirements. From start-up in September
1997 through December 1999, MTBE concentrations have decreased from a range of 70,000
to 100,000 µg/L to a range of 20,000 to 26,000 µg/L. This influent data is presented in
Figure 15, based on detailed performance data shown in Table A-6 of Appendix A.
Unfortunately, the performance of the air stripper cannot be independently evaluated from
the rest of the treatment train because air stripper effluent has not been regularly monitored.
Figure 15.
MTBE influent concentrations at Elmira, California. Note: Effluent MTBE data are not available.
VOC concentrations entering the off-gas treatment system (vapor-phase GAC) from December
1998 through March 2000 are provided in Figure 16. In almost every sampling event, effluent
concentrations were reduced to non-detect (less than 0.1 ppmv). Unfortunately, a limited
number of samples from the original off-gas treatment system contained detectable levels of
MTBE. As shown in Figure 17, the ADDOXTM off-gas treatment system is more reliable than
the vapor-phase GAC. During the first 3 months of operation, the ADDOX6 system treated
600 cfm off-gas containing 65 to 393 ppmv MTBE. Destruction efficiency ranged from 88.3
percent to greater than 99.9 percent.
Annual operating costs for the air stripper include the costs of power, labor, sampling, parts, and
chemicals associated with cleaning, maintenance, and repairs. Annual O&M costs range from
$18,350 to $31,050 (late 1990s). Approximately 4 to 6 hours per week are required to
43
Total Hydrocarbons
TPHg
Benzene
Toluene
Ethylbenzene
Concentration (ppmv)
Xylenes
Note: Effluent samples were taken on
12/01/98 and 1/12/99 show that constituent
concentrations were <0.1 ppmv (ND), with
the exception of the total hydrocarbons
on 12/01/98, which had concentration
of 2.16 ppmv.
VOC Concentration (ppmv)
Figure 16.
Off-gas treatment influent concentrations of BTEX and TPH-G (1998 to 2000) at Elmira, California.
Note: MTBE influent concentrations are shown in Figure 17.
Sample Date
Figure 17.
ADDOXTM performance summary test data at Elmira, California.
44
maintain the entire treatment system. At the time of data collection, the air stripper had only
required cleaning three times (approximately once per year). Minimal replacement parts have
been needed. The capital cost for the air stripper unit and control system ranged from $25,000
to $30,000 (1997 dollars); the capital cost for air stripper appurtenances, including the filters,
oil/water separator, and vapor-phase GAC vessels, was between $75,000 and $100,000.
The capital cost of the ADDOX6 off-gas treatment system is approximately $70,000. The
annual operating cost is projected based solely on the initial operating costs, since the unit
has only been in operation since February 2000. NEEP’s initial O&M cost estimate is based
on assumptions about contaminant levels, the time for adsorption and desorption cycles,
quarterly sampling, and an electrical usage rate of $4,205 per year ($11.52/day). Actual
maintenance and cleaning costs for the system were unknown at the time of data collection
for this report. No major repairs or problems have occurred since system start-up. Routine
maintenance and troubleshooting can be monitored by the NEEP headquarters in New
Hampshire through a modem interface that is installed in the control panel. Capital and
annual operating costs for the ADDOXTM system are included in Table 38.
Table 38. Capital and Annual O&M Costs (1997) at Elmira, California
Capital Costs
Air stripper
ADDOX
$25,000 to $30,000
TM
$70,000
Controls and appurtenances
$75,000 to $100,000
$185,000
$14,910
Annual O&M Costs
Labor (4 to 6 hours/week at $110/hour)
$23,400 to $33,800
Electricity
$7,500 to $10,000
Electricity for ADDOX6
$4,205
Parts for cleaning, maintenance, and repairs
$10,000 to $20,000
Sampling (once per month at $400)
$4,800
1
$61,355
Total annual costs
$76,263
2
$3.53
1Total amounts are based on an average of the given amounts.
2Based on continuous operation at 25 gpm.
45
3. Analysis of System Cost and Performance
3.1 INTRODUCTION
As illustrated by these case studies, a variety of air stripper designs and treatment system
configurations can successfully meet the challenges posed by a range of MTBE
concentrations, influent water quality profiles, and effluent requirements. The nine case
studies presented in Section 2 illustrate the variability in system flow rates, operating
parameters, and air stripper configurations used for full-scale groundwater treatment. A
comparison of the design parameters, performance data, and costs associated with each of
the treatment system is presented in Tables 39 and 40. Although many differences in the
treatment systems are apparent in these tables, several common elements are noticeable as
well. These are detailed in the following sections discussing treatment train design, air
stripper performance, and cost considerations.
Table 39. Comparison of the Design Parameters, Performance, and Costs
Associated with Each of the Packed Tower Air Stripping Systems
LaCrosse,
Kansas
Culver City,
California
Ridgewood,
New Jersey
Rockaway Township,
New Jersey
Drinking water
Yes
No
Yes
Yes
Off-gas treatment
No
Thermal oxidation
No
No
0.021
2.4
Not available
0.05
131
400
160 to 170
Not available
Stripper configuration
6-feet diameter
x 33-feet tall
Fiberglass
(x 2 series)
6-feet diameter
x 39.5-feet tall
(x 3 in series)
5.75-feet
diameter
x 23-feet tall
Two aluminum
towers
(AST-1 and
AST-2)
9-feet diameter
x 25-feet tall
Two strippers
(AS-2 replaced
AS-1 in 1995)
Stripper
operation
start-up date
September 1997
October 1999
1991 (AST-1)
1997 (AST-2)
February 1982 (AS-1)
1995 (AS-2)
Current
Current
Current
1995 (AS-1)
Current (AS-2)
Flow rate (gpm)
350 (winter)
480 (summer)
200
300 (AST-1)
225 (AST-2)
1400 (AS-1)
1500 (AS-2)
Operation mode
8hours/day;
6 day/week
Continuous
75 percent
Continuous
156:1 to 214:1
670:1
110:1 (AST-1)
250:1 (AST-2)
100:1
973
17,000
689 (AST-1)
60 (AS-1)
10 (AS-2)
Location
Iron (mg/L)
Alkalinity as CaCO3
(mg/L)
Stripper operation
termination date
Air-water ratio
Maximum MTBE
(Continued on Next Page)
46
Associated with Each of the Packed Tower Air Stripping Systems
(Continued from Previous Page)
LaCrosse,
Kansas
Culver City,
California
Ridgewood,
New Jersey
Rockaway Township,
New Jersey
Average MTBE (µg/L)
153
4,000
90 (AST-1)
5 to 10 (AS-2)
Effluent MTBE (µg/L)
<10
<2
<70 (Goal)
<1 (Goal)
Location
None
BTEX, TPH-G,TBA
PCE
PCE; TCE; 1,1,1-TCA;
chloroform;
cis-1,2-DCE;
1,1-DCE; 1,1-DCA;
carbon tetrachloride
Total capital costs
$189,968
$1,714,000
$770,000
$300,000
Annual O&M costs
$25,324
$359,000
$72,000
$120,000
Annual cost
$40,633
$497,125
$134,052
$150,000
$0.57 to $0.76
$14.00
$0.64
$0.22
Capital costs
(year 2000 dollars)
$203,816
$1,771,613
$826,131
$338,976
Amortized capital costs
at 7 percent for 30
years
(year 2000 dollars)
$16,425
$142,768
$66,575
$27,317
Annual O&M costs
(year 2000 dollars)
$27,170
$371,067
$77,249
$120,000
Annual cost
(year 2000 dollars)
$43,595
$513,835
$143,824
$147,317
$/1,000 gallons
(year 2000 dollars)
$0.65
$4.89
$1.62
$0.19
Other contaminants
$/1,000 gallons
DCA: Dichloroethane.
DCE: Dichloroethylene.
TCA: Trichloroethane.
47
Associated with Each of the Low Profile Air Stripping Systems
Somersworth,
New
Hampshire
Bridgeport,
Connecticut
Chester,
New Jersey
Mammoth
Lakes,
California
Elmira,
California
Drinking water
No
No
Yes
No
No
Off-gas treatment
No
Catalytic
oxidation
No
GAC
ADDOXTM
treatment
Iron (mg/L)
5.6
21
NA
NA
NA
Alkalinity as
CaCO3 (mg/L)
NA
NA
NA
NA
250 to 350
Stripper
configuration
One 4 tray
low profile
air stripper
Two sets of
parallel low
profile air
strippers (primary
and secondary)
One 4 tray
low profile
air stripper
One
low profile
air stripper
One
low profile
air stripper
Stripper operation
start-up date
December 1996
April 1995
Fall 1998
February 2000
1997
Stripper operation
termination date
May 2000
1998
Current
Current
Current
Flow rate (gpm)
2 to 10
Typically 10
11
15
2 to 15.5
Average 6.5
25
Operation mode
Continuous
Continuous
12 hours/day,
7 days/week
Continuous
Continuous
1,070:1
340:1
75:1
1,870:1
90:1
1,670,000
2,400,000
220
97,000
NA
(210,000 design)
Average MTBE
(µg/L)
77,000
780,000
NA
NA
NA
(9,800 design)
Effluent MTBE
(µg/L)
<5,000
50
14
<0.5
<1.0 (design)
Other
contaminants
BTEX
BTEX
TCE
BTEX, TPH-G
BTEX, TBA, DIPE,
ETBE, TAME,
TPH-G, TPH-D
Total capital costs
$42,923
$530,000
$15,000
NA
$185,000
Annual O&M costs
$15,480
$48,000
$4,462
NA
$61,355
Annual cost
$18,939
$90,710
$5,670
NA
$76,263
Location
Air-water ratio
Maximum MTBE
concentration
(µg/L)
48
Associated with Each of the Low Profile Air Stripping Systems
Somersworth,
New
Hampshire
Bridgeport,
Connecticut
Chester,
New Jersey
Mammoth
Lakes,
California
Elmira,
California
$/1,000 gallons
$22.00
$15.69
$1.44
NA
$3.53
Capital costs
(year 2000 dollars)
$47,109
$598,858
$15,504
NA
$198,486
Amortized capital
costs at 7 percent for
30 years
(year 2000 dollars)
$3,796
$48,260
$1,249
NA
$15,995
Annual O&M costs
(year 2000 dollars)
$16,990
$52,681
$4,897
NA
$67,338
Annual cost (year
2000 dollars)
$20,786
$100,941
$6,147
NA
$83,333
$/1,000 gallons (year
2000 dollars)
$13.88
$17.46
$1.04
NA
$6.34
Location
NA: Not available.
3.2 TREATMENT TRAIN DESIGN
3.2.1 Pretreatment
In seven of the nine case studies summarized in this report, the extracted groundwater
underwent some type of pretreatment prior to air stripping. The types of pretreatment used
included pH adjustment, water softening, water heating, iron precipitation, oil/water separation,
and biological GAC to reduce nutrient loading prior to the air stripper. The addition of
chemicals to reduce scaling, biological growth, and foaming was also common.
The two case studies examined in this report that did not employ pretreatment were both
packed tower air stripper systems (located in Ridgewood, New Jersey, and Rockaway Township, New Jersey). Both of the systems were primarily designed to treat other VOCs (PCE
and DIPE). MTBE concentrations in the first system were variable, but never required
significant reduction (i.e., the required percent removal was less than 22 percent). In the
second system, influent MTBE concentrations were low, ranging from non-detect (less than
0.5 µg/L) to 12 µg/L and, therefore, did not require significant reduction. Systems without
pretreatment understandably may encounter more operational difficulties associated with
scaling and biofouling, which will reduce the removal efficiency of the air stripper system.
49
3.2.2 Air Stripper System
The configuration of the air stripper unit is one of the most obvious design choices. The case
studies included in this review demonstrate that the appropriate configuration is determined
primarily by the system flow rate. Systems with flow rates greater than 100 gpm were packed
tower configuration; those less than 100 gpm were low profile air strippers. Other site
constraints may influence the choice of air stripper design, particularly for systems with flow
rates between 50 and 200 gpm. Packed tower units are more compact and require a reduced
footprint area. However, the packed tower configuration is also more conspicuous than a low
profile air stripper. The heights of packed tower systems analyzed in this report ranged from
25 to 35 feet.
Air stripping units were used at two of the case study sites as interim treatment systems. Due
to site-specific time constraints for implementing the interim remedy, pilot-testing was not
conducted prior to system installation and full-scale use. At another site (Ridgewood, New
Jersey), the air stripping unit was originally designed to address VOC contamination.
Therefore, the design process was quite different at these sites. The use of air stripping as a
temporary or interim remedy at these sites illustrates the convenience of this technology for
quickly addressing MTBE contamination.
Long-term or permanent air stripping system designs vary from site to site due to the desired
amount of redundancy (i.e., factor of safety) and desired effluent quality. Since MTBE is not
regulated under the Safe Drinking Water Act, air stripper systems in different states are
required to meet different effluent concentrations for MTBE. Two of the case studies appear
to have been over-designed; treatment train components were installed to ensure system
reliability, but were not needed. At one of these two sites, the unused treatment train
component was taken offline, but was later needed in response to a second UST release that
increased influent MTBE concentrations. The balance between over-designing and underdesigning is site-specific. Long-term site plans, available funding, and state, local, and owner
perceptions of acceptable system reliability and redundancy must be taken into account.
The potential decline in MTBE influent concentrations over time should be considered
during treatment system design. At five of the nine case studies discussed in this report,
MTBE concentrations declined over time. Two of the systems no longer needed to operate
after the first 3 to 6 years because MTBE concentrations were consistently low or non-detect.
The ability to scale down the treatment system in response to declining influent
concentrations would improve system cost-effectiveness.
3.2.3 Post-Treatment
Post-treatment processes were common at sites examined in this report, regardless of whether
treated water was used for drinking water or merely discharged into the environment. Posttreatment was not needed at only two systems prior to discharge or disinfection and use.
50
Liquid-phase GAC was employed at six treatment systems; sand and anthracite filtration was
used at the seventh site. These filtration systems were designed to polish water quality and
provide an extra degree of safety to ensure that treatment system effluent met discharge
requirements. Post-treatment filtration was not designed to achieve VOC removal at any of
the case study sites.
One of the sites needed to employ additional post-treatment for VOC removal. At the packed
tower air stripping system in Culver City, California, a UV/H2O2 system was installed after
the air stripping unit to disinfect and provide additional removal of oxygenates, including
TBA. Although air stripping was found to remove up to 90 percent of TBA at one of the case
study sites (Culver City, California), TBA is more difficult to remove from water than MTBE
and may govern air stripping design or require the use of post-air stripper advanced oxidation
to meet effluent TBA requirements. In summary, while post-treatment is commonly used to
address other VOCs or provide a safety factor, it is not common to use several treatment
technologies in series to remove MTBE.
3.2.4 Off-Gas Treatment
Four of the nine sites included in the case study analysis treated off-gases from the air stripper
units before emitting them to the atmosphere. Technologies used include thermal oxidation,
catalytic oxidation, vapor-phase GAC, and an adsorption/thermal desorption and destruction
system commercially available as the ADDOXTM system. While regulations vary nationwide,
the need for an off-gas treatment system is typically governed by the expected mass released
to the atmosphere per day. Emission requirements depend on state and local air quality
regulations and on the proximity of potential receptors. Data from the four case studies was
not sufficient to compare the design considerations of different types of off-gas treatment
systems.
3.3 TREATMENT SYSTEM PERFORMANCE
3.3.1 MTBE Removal
The case studies demonstrate that air strippers can successfully treat groundwater with
influent MTBE concentrations as high as 2,400,000 µg/L (Bridgeport, Connecticut) and as
low as 10 µg/L (Rockaway Township, New Jersey). Depending on the design and operation
of the air stripping system, average MTBE removal efficiencies ranged from 65 percent to
greater than 99.99 percent at the nine case studies included in this report.
For the packed tower air stripping systems, average MTBE removal efficiencies were greater
than 90 percent, with the exception of the site in Rockaway Township, New Jersey (where,
on average, only 65 percent of MTBE was removed), and the site in Ridgewood, New Jersey
(where approximately 30 percent was removed). However, the system at Rockaway
Township, New Jersey, had low influent MTBE concentrations. Effluent MTBE
51
concentrations at this system were typically non-detect (less than 0.5 µg/L) and never
exceeded 2 µg/L. The system at Ridgewood, New Jersey, was not designed for MTBE
removal, but rather for PCE treatment. At the other packed tower treatment systems, effluent
MTBE concentrations ranged from less than 2 µg/L to approximately 70 µg/L and were
consistently below the state-specific standard for MTBE.
For the low profile air stripping systems, average MTBE removal efficiencies were all
greater than 90 percent. Average MTBE concentrations in treatment system effluent ranged
from non-detect (less than 1 µg/L) to approximately 460 µg/L (site at Somersworth, New
Hampshire). As with the packed tower air strippers, low profile air stripper performance was
sufficient to meet the state MTBE standard.
Although four of the case study air stripping systems implemented off-gas treatment,
performance data were only available for two of the systems (Mammoth Lakes, California,
and Elmira, California). At Mammoth Lakes, influent concentrations to the vapor-phase
GAC system ranged from 15 to 590 parts per billion by volume (ppbv) MTBE. Capture and
destruction values for MTBE ranged from 93.3 to 99.7 percent. At Elmira, California,
influent concentrations to the ADDOXTM off-gas treatment system were higher, ranging from
65,000 to 393,000 ppbv MTBE. Capture and destruction efficiency for the ADDOXTM
system ranged from 88.3 to 99.9 percent.
3.3.2 System Reliability
Fouling and scaling were not an issue for most of the case study treatment systems,
presumably because of the pretreatment systems described in Section 3.2.1. Iron
concentrations were fairly low in treatment system influent, ranging from 0.02 to 21 mg/L.
Iron precipitation is lessened by a neutral or slightly acidic pH. Typically, the pH of influent
water was neutral or slightly basic; pH ranged from 6.6 to 8.7. At one system (Somersworth,
New Hampshire), a buildup of silt resulted in a temporary system shutdown. This was
addressed by increasing the frequency of air stripper cleaning.
A common theme among the case studies was fluctuations in influent MTBE concentrations
that resulted in fluctuations in effluent concentrations. One response to increase system
reliability is to address influent fluctuations. As discussed in Section 2.1.3, spikes in influent
MTBE concentrations at the site in LaCrosse, Kansas, were dampened by limiting pumping
from the most contaminated well. Another possibility is to install a blending tank prior to the
air stripper influent. At other sites (e.g., Somersworth, New Hampshire), the efficiency of the
air stripper system declined gradually over time as silt and other particles built up. After
cleaning, air stripper efficiency improved greatly. Swings in operating efficiency can be
addressed by better pretreatment systems or increasing the frequency of cleaning.
Air stripper efficiency also decreases with temperature. Several air stripper systems reported
this as a consideration (LaCrosse, Kansas, and Bridgeport, Connecticut). However,
52
temperature effects do not seem to be as important as the buildup of silt or changes in influent
concentrations. For example, at the Connecticut site, the lowest removal efficiency was
measured in August 1995. The impact of reduced temperatures during the winter months is
not apparent in the case study performance data presented in this report. However, air
stripping systems located in colder climates will have noticeably higher O&M costs during
the winter months since these systems are typically equipped with heating elements.
3.4 TREATMENT SYSTEM COSTS
Capital costs for the air stripping systems were reported to range from $15,000 ($ 1998) to
$1.7 million (late 1990s). When expressed in year 2000 dollars to enable a direct comparison
between system costs, capital costs ranged from $15,500 to $1.77 million. Normalized by the
design capacity of the system, capital costs ranged from $0.47/1,000 to $104/1,000 gallons
capacity. Taking the design log removal of MTBE into account, capital costs still ranged
widely, from $0.47/1,000 to $85/1,000 gallons/log removal.
Costs per kilogallon ($2000)
Based on our review of the nine case studies presented in this report, O&M costs for air
strippers were a function of both system flow rate and performance, as shown in Figure 18.
The data illustrate efficiency of scale (i.e., lower unit O&M costs [$/1,000 gallons treated] as
the size of the air stripping unit increased). The data also demonstrate that costs increase with
percent removal of MTBE, as expected. Costs ranged from approximately $1 to $10/1,000
gallons for systems achieving greater than 90 percent removal. Costs were approximately
$0.15 to $1/1,000 gallons for treatment systems achieving between 65- and 90-percent
removal.
Flowrate (gpm)
Figure 18.
Cost summary of MTBE removal by air stripping.
Note: No cost data available for the site at Mammoth Lakes, California.
53
4. Model Evaluation
4.1 OVERVIEW OF MODELING SOFTWARE PROGRAMS
The performance data from five of the nine air stripper case studies were used to evaluate the
accuracy of two models that are commonly used to estimate the performance of low profile and
packed tower air strippers. The models chosen for this exercise include NEEP ShallowTray®
Modeler software and the ASAPTM Packed Tower Model (Michigan Technological University,
2005).
4.1.1 North East Environmental Products (NEEP) Shallow Tray®
Low Profile Air Stripper Model
NEEP is a manufacturer of packed tower air strippers and low profile shallow tray air
strippers (North East Environmental Products, 2005). As part of the quality testing, NEEP
analyzed the performance of its commercially available ShallowTray® low profile air stripper
by analyzing over 10,000 samples to test the air stripper’s performance at full-scale for
removing VOCs (USEPA Method 624). Results were used to create performance curves
illustrating removal efficiency at different VOC concentrations, temperatures, and flow rates.
These performance curves are used in the proprietary ShallowTray® Modeler software to
simplify the process of predicting the performance of ShallowTray® air stripping systems
under different operating conditions. The ShallowTray® model calculates removal versus
flow rate for several contaminants, including BTEX, MTBE, and chlorinated VOCs. The
model accounts for contaminant solubility, vapor pressure, water temperature, air temperature, and influent concentrations.
4.1.2 Aeration System Analysis Program (ASAPTM) Packed Tower Model
The ASAPTM model was developed at Michigan Technological University and is commercially available separately or in a package with other modeling software as a comprehensive
modeling tool known as the Environmental Technologies Design Option Tool (ETDOT)
(Michigan Technological University, 2005). ASAPTM uses mass transfer calculations to
predict the performance of various air stripping designs, including packed towers, systems
with bubble or diffused aeration, and systems with surface aeration. Since these calculations
require chemical-specific properties (e.g., molecular weight, boiling point, Henry’s law
constant, liquid and gas diffusion coefficients, aqueous solubility), ASAPTM is linked to a
program called Software to Estimate Physical Properties (StEPP), which contains the
physical and chemical properties for over 600 compounds, many of which are designated
USEPA priority pollutants. StEPP calculates the value of these properties at the specified
temperature and pressure.
The ASAPTM Packed Tower Aeration Model is designed to predict the performance of
counter-current packed tower air strippers. This model calculates removal efficiency using
54
several simplifying assumptions, including steady-state, plug-flow reactor conditions for
both air and water streams, clean influent air stream, and equilibrium of contaminant
concentrations in air and water phases, as described by Henry’s Law (ASAP, 2005). The
model can be used to assess the preliminary design and feasibility of air stripping processes,
plan pilot-scale studies, or interpret pilot-scale results.
Model calculations can be performed in either the design or rating mode. In the design mode,
the user specifies the required removal efficiency and the packed tower is then sized to meet
the treatment objectives for all contaminants. Model output includes the packed tower design
and effluent concentration for each contaminant of concern. In the rating mode, the
performance of an operating packed tower can be compared with the expected performance
to see if the air stripper is operating effectively. Actual operating parameters (e.g.,
temperature, contaminants, concentrations, packing material characteristics) are entered into
the model by the user or chosen from the model’s built-in database. The model-predicted
removal efficiency is compared with observed removal efficiencies to see if the air stripper
is meeting expectations. Additional information about the ASAPTM model can be found
online (Michigan Technological University, 2005) or in Hokanson et al., 1995.
4.2 LOW PROFILE AIR STRIPPER — SOMERSWORTH, NEW HAMPSHIRE
4.2.1 Modeled Scenarios
The removal efficiency predicted by the NEEP ShallowTray® Model was compared with the
actual performance of the low profile air stripper operating in Somersworth, New
Hampshire. Six different sets of parameters, or “cases,” were modeled, as shown in Table 41.
Each case was tested at temperatures ranging between 66 to 70°F, centered around the
average temperature of the effluent of 68°F. Cases One and Two had water flow rates of 3 and
10 gpm, respectively, to reflect the minimum and maximum water flow rates of the system.
Case Three used an air-to-water ratio of approximately 800, which was typically maintained
during system operation. For these three cases, the maximum air flow rate of 900 scfm was
held constant to reflect the measured air-to-water ratio of 1,070. For Cases Four, Five, and
Six, the water flow rate of 10 gpm was kept constant and the air flow rate was varied at 600,
675, and 750 scfm, respectively. Data for each case can be found in Table B-1 of Appendix B.
Table 41. Modeling Scenarios for Low Profile Air Stripper at Somersworth, New Hampshire
Parameter
Water flow rate
(gpm)
Air flow rate
(scfm)
Air-water ratio
Temperature (°F)
Actual
Case 1
Case 2
Case 3
Case 4
Case 5
Case 6
3 to 10,
typically 10
3
10
8.4
10
10
10
900
900
900
900
600
675
750
1,070:1
2,244:1
673:1
801:1
450:1
505:1
560:1
68
66 to 70
66 to 70
66 to 70
66 to 70
66 to 70
66 to 70
55
4.2.2 Discussion
A comparison of the theoretical and actual effluent MTBE concentrations shows that the
model predicted greater MTBE removal than what was actually observed. From August 1997
through April 1998, actual effluent concentrations were significantly higher than the
estimated effluent concentrations, most likely due to the build-up of silt that occurred in the
stripper. In Cases Four, Five, and Six, the effluent concentrations were greater than the first
three cases, but the model still predicted lower effluent concentrations than produced by the
actual system.
4.3 LOW PROFILE AIR STRIPPER — CHESTER, NEW JERSEY
Data from the site at Chester, New Jersey, was verified using the NEEP ShallowTray®
Modeler software. Only one scenario was modeled for this site, which can be described as
follows:
• NEEP Shallow Tray Low Profile Air Stripper: Model # 2641.
• Water flow rate 15 gpm.
• Air flow rate 150 scfm.
• Typical air-to-water ratio 75 to 1.
• Operational water temperature 40 to 45°F.
Based on performance data, the influent MTBE concentration was fixed at 220 µg/L.
4.3.2 Discussion
The model estimated an effluent MTBE concentration ranging from 74 to 86 µg/L for the
varying temperatures, resulting in removal efficiencies ranging from 61 to 67 percent. The
only effluent MTBE concentration provided for this site (less than 14 µg/L) was measured
after the GAC polishing step, so no direct comparison to actual performance can be made.
Therefore, the overall removal efficiency through the GAC polishing step is estimated to be
greater than 81 percent, based on model data.
4.4 PACKED TOWER AIR STRIPPER — LACROSSE, KANSAS
The removal efficiency predicted by the ASAPTM Packed Tower Model was compared with
data from the packed tower air stripper operating in LaCrosse, Kansas. Two different cases
were modeled to reflect differences between summer and winter flow rates. Typical operating
56
parameters and modeled cases are shown in Table 42. As indicated, flow rates of 480 and 350
gpm were used to represent summer and winter flow rates. Temperatures of 60 and 70°F were
used for all of the tested parameters since the influent water temperature was unknown. An
air flow rate of 10,000 cfm was used in the model, resulting in air-to-water ratios of 156 and
214. MTBE influent concentrations ranged from 46 to 954 µg/L for both modeled and actual
scenarios. Effluent data was modeled for each of the two stages of the packed towers.
Table 42. Modeling Scenarios for Packed Tower Air Stripper at LaCrosse, Kansas
Parameter
Air flow rate (scfm)
Air-water ratio
Temperature (°F)
Actual
Case 1
Case 2
480 (summer)
350 (winter)
480
350
10,000
10,000
10,000
156:1 to 214:1
156:1
214:1
Not available
60 to 70
60 to 70
4.4.2 Discussion
A comparison of the actual and theoretical concentrations modeled at each stage of the air
stripper is presented in Tables B-2 and B-3 of Appendix B. The predicted effluent
concentrations demonstrate better removal efficiencies than the actual effluent data. For 480
gpm, the model predicted a removal efficiency of 99 percent; for 350 gpm, the model
predicted a removal efficiency of 99.5 percent. Actual data showed that the removal
efficiency ranged from 41 to 100 percent.
4.5 PACKED TOWER AIR STRIPPER — CULVER CITY, CALIFORNIA
ASAPTM model predictions were compared with actual removal efficiencies at a packed tower
air stripper operating in Culver City, California. Packing properties (i.e., nominal size 2.5
inches, geometric surface area 55 square feet per cubic feet [ft2/ft3], polypropylene material
density 5.1 pounds per cubic feet [lbs/ft3]) were inputted to the user-defined database
because the actual packing material (No. 2 NUPACTM) was not available in the model. A
temperature of 70°F was tested in the model to reflect the temperature range observed in the
operational data for the system. Design parameters used in the model included the following:
• Water flow rate 200 gpm.
• Air flow rate 7,000 scfm.
• Typical air-to-water ratio 700 to 1.
• Operational temperature 70°F.
57
Actual MTBE concentrations entering the air stripper at Culver City, California, from
November 1999 through March 2000 were used in the model.
4.5.2 Discussion
Based on a comparison of the data, the model predicted lower effluent concentrations (0.04
to 0.06 µg/L) than the actual effluent data (1.1 to 8.4 µg/L). A comparison of the actual and
theoretical concentrations modeled at each stage of the air stripper is presented in Table B-4
of Appendix B.
4.6 PACKED TOWER AIR STRIPPER — ROCKAWAY TOWNSHIP, NEW JERSEY
4.6.1 Modeled Scenario
The predicted air stripper removal using the ASAPTM model was compared with actual
removal from a packed tower air stripper operating in Rockaway Township, New Jersey.
Temperatures of 50 and 55°F were used in the two modeling cases to reflect operational data
for the system. A water flow rate of 1,500 gpm and an air-to-water ratio of 100 were used in
the model. Actual influent MTBE concentrations observed in the performance data for the
1995 treatment system were also used in the model. Actual operating parameters and
modeled input parameters for each case are shown in Table 43.
Table 43. Modeling Scenarios for Packed Tower Air Stripper
at Rockaway Township, New Jersey
Parameter
Actual
Case 1
Case 2
1,500
1,500
1,500
Air flow rate (cfm)
20,000
20,000
20,000
Air-water ratio
100:1
100:1
100:1
50 to 55
50
55
Temperature (°F)
4.6.2 Discussion
A comparison of the actual and theoretical concentrations modeled at each stage of the air
stripper is presented in Table B-5 of Appendix B. The comparison shows that the model
predicted lower effluent concentrations than the actual effluent data. The model predicted
removal efficiencies ranging between 93 and 96 percent through the air stripper; actual
removal efficiencies ranged between 14 and 91 percent.
4.7 SUMMARY OF MODELING RESULTS
The ASAPTM model predicted slightly better removal efficiency and slightly lower effluent
MTBE concentrations than actual packed tower air stripping units at the four sites included
58
Predicted Removal
in the modeling analysis. There may be several reasons for this discrepancy. The ASAPTM
model assumes that the hydraulic configuration of the packed tower reactor is plug flow for
both air and water streams. This is the most efficient configuration. During actual system
operation, some mixing, short-circuiting, or other non-ideal flow patterns may occur,
reducing the effectiveness of contaminant-phase transfer from liquid to vapor. The percent
removal predicted using the NEEP model was in general agreement with the observed
concentration at the field site. A comparison of modeling results and actual system
performance is shown in Figure 19.
Actual Removal
Figure 19.
Comparison of modeling results to actual performance.
On average, observed removal efficiencies were approximately 15 percent lower (ranging
2 percent higher to 50 percent lower) than modeling predictions. The highest discrepancy
between predicted and observed percent removal occurred for the site at Rockaway
Township, New Jersey, where concentrations of MTBE were already fairly low in the influent
(ranging from less than 0.5 to 6.9 µg/L MTBE over the period of operation used for the
modeling exercise). Model predictions showed better agreement with actual system
performance at systems with higher influent MTBE concentrations (e.g., Culver City,
California, and Somersworth, New Hampshire). The ability of these models to accurately
predict air stripper performance contributes to the growing acceptance of air stripping as a
proven technology to remove MTBE from groundwater supplies.
59
5. Summary of Findings
The California MTBE Research Partnership identified a research need to assess the efficacy
of air stripping for removing MTBE from contaminated groundwater. MTBE contamination
has been reported at UST sites across the country. Although air stripping is a well-established
technology for VOCs, like PCE, the technology has not yet been demonstrated to be costeffective or reliable for MTBE treatment. As summarized in this report, the Partnership
identified nine sites where air strippers are being used to address MTBE contamination in
groundwater. The Partnership obtained cost and performance data for each of the sites and
analyzed the data to assess the benefits, limitations, and costs of air stripping for MTBE. Two
commercially available models for predicting air stripping performance were assessed by
comparing model predictions with operating performance at several of the case study sites.
Study findings, conclusions, and recommendations are summarized in this section.
5.1 CASE STUDY DATA COLLECTION
Through research efforts, nine air stripper systems operating at full-scale to address MTBE
contamination were identified. Information about site history, air stripper system design,
configuration, influent MTBE concentrations, other influent water quality parameters,
effluent MTBE goals, capital costs, and annual O&M costs were collected for each site.
These data were provided to the Partnership by environmental consultants, air stripper manufacturers, and state regulators. Some of the data could not be shared with the Partnership due
to ongoing litigation. Nevertheless, enough data was available to proceed with data analysis
and model validation.
5.2 CASE STUDY DATA ANALYSIS
The case study analysis indicated that a variety of different treatment train configurations can
use air strippers to successfully remove a wide range of MTBE concentrations. Influent
MTBE concentrations were as high as 2,400,000 µg/L and as low as 10 µg/L in the case
studies included in this report. Average MTBE removal efficiencies ranged from 65 percent
to greater than 99.9 percent, with the lower range occurring in systems that did not require
significant MTBE reduction.
Most of the air stripper system designs included some form of pretreatment to reduce the
possibility of scaling, biological growth, and foaming. Heating elements were included prior
to air stripping in colder climates. Fouling and scaling were not an issue for most of the case
study treatment systems because of this pretreatment. A buildup of silt occurred in one
system, resulting in a temporary system shutdown. This problem was addressed by cleaning
the air stripper more frequently. Sites that did not employ pretreatment were designed to
primarily remove other VOCs and did not require significant MTBE reduction.
60
Air stripper configuration was primarily determined by the economics of different flow rates.
Systems with flow rates below approximately 100 gpm were low profile systems; those with
flow rates greater than 100 gpm were packed tower configurations. Air strippers were used
as interim treatment systems at some of the sites. Since air stripping is quick to implement,
it is advantageous compared to other treatment methods (e.g., biological systems). Another
advantage of air strippers is the applicability to other VOC contaminants. However, at sites
with MTBE and TBA, the desired TBA removal may drive air stripping design considerations
or necessitate post-treatment specific to TBA.
Post-treatment was not needed for MTBE removal; however, GAC or other filtration systems
were frequently used as a polishing step. Off-gases treatment technologies were needed at
four of the nine case study sites. Technologies included thermal oxidation, catalytic
oxidation, vapor-phase GAC, and an adsorption/thermal desorption system known as
ADDOXTM. Data were not sufficient to compare the cost and performance of different types
of off-gas treatment systems.
Influent MTBE concentrations declined over time at five of the nine case study sites. Two of
the air stripping systems were no longer needed after 3 and 6 years of operations since
influent concentrations were below discharge standards or were non-detect. Fluctuations in
influent MTBE concentrations and swings in operating efficiency were common at the air
stripper case studies, but were successfully addressed by changing well usage patterns and
increasing the frequency of cleaning. Air stripper efficiency also decreases with temperature.
However, temperature effects were secondary to the effects of silt buildup or changes in
influent concentrations. Systems in colder climates will understandably have higher O&M
costs in winter due to heating costs.
Capital costs for the air stripper systems ranged from $43,000 ($1997) to $1.7 million (late
1990s). Normalized by flow rate and expressed in year 2000 dollars, capital costs ranged
from $0.47/1,000 to $103/1,000 gallons ($0.47/1,000 or $85/1,000 gallons/log removal).
O&M costs were also a function of system flow rate and percent MTBE removal. Costs
ranged from $1 to $10/1,000 gallons for systems achieving greater than 90-percent removal.
Costs were approximately $0.15 to $1/1,000 gallons for systems achieving between 65- and
90-percent removal.
5.3 MODEL VALIDATION
Two different air stripping models were validated using performance data from several low
profile and packed tower air stripper case studies. The ASAPTM model created at Michigan
Technological University was used to simulate the performance of three packed tower air
strippers operating at LaCrosse, Kansas; Culver City, California; and Rockaway Township,
New Jersey. In this modeling program, operating parameters, such as influent MTBE
concentrations, air-to-water ratio, water flow rate, temperature, tower dimensions, and
packing media, were specified. The model was used to predict effluent MTBE
61
concentrations. Predicted effluent concentrations were slightly lower than the observed
concentrations at all four sites. Thus, the model-predicted removal efficiencies were slightly
greater than observed efficiencies.
For the low profile air strippers, a model created by NEEP was used to estimate effluent
MTBE concentrations. A number of parameters were specified in the model, including airto-water ratio, temperature, and flow rates. As with the ASAPTM model, the NEEP model
predicted slightly lower effluent MTBE concentrations than those observed at the low profile
air stripper operating in Somersville, New Hampshire. Despite the optimistic bias of these
two models in predicting more MTBE removal than was actually observed, the models
agreed with observed removal efficiency within 15 percent. Model predictions showed even
better agreement with actual system performance at systems with higher influent MTBE
concentrations. The data illustrate that commercially available models are fairly accurate in
predicting actual air stripper performance.
5.4 CONCLUSIONS
Based on this review of air stripper systems that are operating to address MTBE
contamination, air strippers can be used to successfully and reliably remove MTBE from
drinking water supply systems or groundwater remediation systems. This study provides a
brief overview of water quality parameters, air stripper design and performance data, and
cost summaries for each case study. MTBE was successfully removed, with efficiencies
greater than 90 percent, over a wide range of influent concentrations. Commercially available
models have been demonstrated to predict actual MTBE removal efficiency to within 15
percent. Although model predictions of removal efficiency were biased slightly high, the
models provide a valuable tool for assessing air stripper performance during remedy
selection and conceptual treatment system design. Expressed in year 2000 dollars, capital
costs ranged widely, from $0.47/1,000 to $103/1,000 gallons capacity. O&M costs associated
with the case studies ranged from $0.15 to $11/1,000 gallons of water treated.
62
6. References
California MTBE Research Partnership (1999). Evaluation of the Applicability of Synthetic Resin
Sorbents for MTBE Removal from Water. National Water Research Institute, Fountain Valley,
California.
California MTBE Research Partnership (2000). Treatment Technologies for Removal of MTBE from
Drinking Water: Air Stripping, Advanced Oxidation Processes, Granular Activated Carbon, Synthetic
Resin Sorbents, Second Edition. National Water Research Institute, Fountain Valley, California.
California MTBE Research Partnership (2001). Treating MTBE-Impacted Drinking Water Using
Granular Activated Carbon. National Water Research Institute, Fountain Valley, California.
California MTBE Research Partnership (2004). Evaluation of MTBE Remediation Options. National
Water Research Institute, Fountain Valley, California.
Hokanson, D.R., T.N. Rogers, D.W. Hand, F. Gobin, M.D. Miller, J.C. Crittenden, and J.E. Finn
(1995). “A Physical Property Resource Tool for Water Treatment Unit Operations.” Proceedings of
AWWA Annual Conference, Anaheim, California, pp. 411-422.
Michigan Technological University (2005). Environmental Technologies Design Option Tool,
ETDOT TM. Available online at www.cpas.mtu.edu/etdot.
North East Environmental Products (2005). North East Environmental Products, Inc Integrated
Environmental Technologies. Available online at www.neepsystems.com
Suflita, J.M., and M.R. Mormile (1993). “Anaerobic Biodegradation of Known and Potential
Gasoline Oxygenates in the Terrestrial Subsurface.” Environmental Science and Technology, 27(6):
976-978.
US Water News (1996). “Santa Monica Water Supply Threatened by MTBE.” US Water News Online.
July. Available online at www.uswaternews.com/archives/arcquality/6smonica.html
U.S. Environmental Protection Agency (1998). Oxygenates in Water: Critical Information and
Research Needs. Office of Research and Development, Washington, D.C. EPA/600/R-98/048.
U.S. Environmental Protection Agency (2005). Contaminant Focus: Methyl Tertiary Butyl Ether.
Technology Innovation Program. Available online at www.clu-in.org.
Yeh, C.K., and J.T. Novak (1995). “The Effect of Hydrogen Peroxide on the Degradation of Methyl
and Ethyl Tert-Butyl Ether in Soils.” Water Environment Research, 67(5): 828-834.
63
64
Appendix A
Table A-1.
Air Stripper Performance Data for MTBE at La Cross, Kansas
To
Tower (µg/L)
2nd Tower
Removal
Efficiency
(%)
Tap
(µg/L)
–
287
26
353
398
–
242
39
255
4/27/1997
393
–
210
47
240
4/28/1997
400
–
224
44
250
4/29/1997
589
–
359
39
310
5/6/1997
80.6
–
56.1
30
57.6
5/13/1997
140
–
74.3
47
61.5
5/21/1997
129
–
146
-13
94.4
5/27/1997
153
–
153
0
131
6/4/1997
143
–
16.3
89
176
6/16/1997
66
–
83.3
-26
83.6
6/23/1997
130
–
275
-112
318
7/1/1997
129
–
77.3
40
82.6
7/8/1997
143
–
154
-8
–
7/10/1997
–
–
154
7/16/1997
143
–
97.4
32
103
7/22/1997
84.3
–
84
0
86.4
7/30/1997
143
–
79.2
45
78
8/5/1997
139
–
162
-17
276
8/12/1997
156
–
76.5
51
56.1
8/26/1997
164
–
368
-124
310
9/2/1997
167
–
163
2
158
9/9/1997
162
–
149
8
149
9/10/1997
161
16.1
90
<0.2
99
152
9/16/1997
138
13.8
90
<0.2
99
6.88
9/17/1997
142
12.6
91
<0.2
98
5.75
9/18/1997
139
14
90
<0.2
99
<0.2
9/23/1997
151
13.3
91
<0.2
98
<0.2
9/24/1997
147
14.1
90
<0.2
99
<0.2
9/30/1997
136
14.3
89
<0.2
99
3.87
10/8/1997
107
11.4
89
<0.2
98
<0.2
10/14/1997
115
<0.2
100
<0.2
–
<0.2
10/21/1997
46.1
14.9
68
<0.2
99
66.1
Date
Influent
(µg/L)
Between
Stripper
(µg/L)
4/25/1997
389
4/26/1997
1st Tower
Removal
Efficiency
(%)
154
65
Table A-1.
Date
Influent
(µg/L)
Between
Stripper
(µg/L)
1st Tower
Removal
Efficiency
(%)
To
Tower (µg/L)
2nd Tower
Removal
Efficiency
(%)
Tap
(µg/L)
10/29/1997
129
11
91
<0.2
98
3.96
11/18/1997
140
14
90
<0.2
99
58
12/9/1997
52.6
13.1
75
3.33
75
3.64
12/29/1997
954
168
82
29.4
83
48.9
1/13/1998
159
35.1
78
19.3
45
231
1/26/1998
197
51.4
74
–
–
71.2
2/11/1998
93.9
17.9
81
4.02
78
<0.2
2/24/1998
125
23.9
81
5.01
79
38.1
3/3/1998
290
171
41
51.1
70
12.9
3/3/1998
973
220
77
51.4
77
14.2
3/10/1998
71.8
15.8
78
3.92
75
6.07
3/10/1998
98.5
20
80
4.75
76
6.75
3/18/1998
93.2
19
80
2.99
84
7.41
3/18/1998
85.1
18
79
4.05
78
9.11
3/24/1998
90
17.1
81
–
–
3/24/1998
99.3
18.6
81
–
–
3/25/1998
–
–
4
3.78
3/25/1998
–
–
4/1/1998
88.4
17.2
81
3.92
3.68
79
3.64
9.83
4/1/1998
110
19.9
82
4.08
79
10.5
4/9/1998
115
18
84
3.1
83
17.3
4/15/1998
99.7
<0.2
100
<0.2
–
<0.2
4/21/1998
84
13.9
83
<0.2
99
<0.2
4/28/1998
97.6
13.3
86
<0.2
98
5.32
5/6/1998
83
8.4
90
<0.2
98
11.4
5/13/1998
110
10
91
<0.2
98
5.5
5/20/1998
98
15
85
2.6
83
16
5/27/1998
39.5
6.92
82
1.26
82
4.36
6/2/1998
91
16
82
2.5
84
5.6
6/9/1998
100
16
84
2.9
82
12
6/16/1998
92
16
83
2.6
84
3.7
6/24/1998
73
12
84
7.4
38
3.5
7/1/1998
87
13
85
2
85
2.8
7/7/1998
82.9
11.4
86
1.2
89
1.17
7/14/1998
227
29.5
87
2.46
92
7.14
7/21/1998
62.6
10.5
83
<0.2
98
2.85
7/28/1998
94.9
10.4
89
1.04
90
4.39
66
Table A-1.
Date
Influent
(µg/L)
Between
Stripper
(µg/L)
1st Tower
Removal
Efficiency
(%)
To
Tower (µg/L)
2nd Tower
Removal
Efficiency
(%)
Tap
(µg/L)
8/4/1998
108
12.7
88
2.08
84
20.8
8/11/1998
110
12.2
89
<0.2
98
27.5
8/19/1998
87.7
11.2
87
1.34
88
10.7
8/26/1998
70.4
12.6
82
<0.2
98
2.84
9/1/1998
108
15.2
86
3.03
80
23.6
9/9/1998
86.1
16.7
81
2.42
86
4.94
9/16/1998
85.3
15
82
2.55
83
5.01
9/30/1998
731
124
83
19.6
84
6.52
10/6/1998
88.9
16.5
81
4.32
74
3.78
10/14/1998
101
19.7
80
4.55
77
<0.2
10/20/1998
86.4
12.4
86
2.37
81
7.02
10/28/1998
77.7
12.7
84
2.53
80
6.09
11/3/1998
107
11.7
89
3.19
73
2.83
11/12/1998
73.3
17.6
76
5.22
70
7.96
11/18/1998
116
15.1
87
7.41
51
14.8
11/24/1998
121
12.6
90
1.03
92
1.38
12/2/1998
94
9.86
90
0.58
94
1.63
12/8/1998
143
16.5
88
3.29
80
3.58
12/16/1998
102
16
84
3.05
81
4.85
12/21/1998
339
52.6
84
9.82
81
2.9
12/28/1998
93.3
11.6
88
1.31
89
7.38
1/6/1999
72.8
8.9
88
1.45
84
2.93
1/12/1999
76.7
11.4
85
1.78
84
11
2/3/1999
87.6
11.8
87
1.29
89
2.52
3/3/1999
108
14.3
87
2.65
81
2.82
4/6/1999
<0.2
<0.2
5/5/1999
108
4.9
95
0.28
94
35.8
6/1/1999
134
29.4
78
7.98
73
15.2
7/7/1999
87.4
12.2
86
2.53
79
13
7/7/1999
132
19.6
85
–
–
8/3/1999
–
–
4.11
8.68
<0.2
<0.2
9/1/1999
78
11.5
85
1.62
86
1.28
9/29/1999
127
24
81
4.81
80
7.05
11/3/1999
109
17.5
84
3.04
83
5.93
12/1/1999
136
32.1
76
8.13
75
12.2
1/5/2000
161
26.4
84
8.04
70
24.2
2/1/2000
137
39.7
71
9.34
76
12.2
67
Table A-2.
Air Stripper Performance Data for MTBE at Somersworth, New Hampshire
Date
Flow
(gallons)
Influent
(µg/L)
Midfluent
(µg/L)
Effluent
(µg/L)
11/22/96
4,463
988,000
8
<5.0
11/23/96
7,290
1,290,000
<2.0
<5.0
11/24/96
72,359
886,000
<2.0
<5.0
11/27/96
45,998
1,670,000
<2.0
<5.0
12/4/96
76,511
694,000
73,300
<5.0
12/10/96
1,376
NA
NA
<5.0
12/11/96
4,450
NA
NA
<5.0
12/12/96
12,590
129,000
33,900
149
12/16/96
61,908
412,000
31,100
388
12/23/96
85,713
322,000
709
15
12/30/96
129,389
305,000
1,200
15
1/8/97
173,845
380,000
5,520
13
2/4/97
1,240,000
<2.0
2/28/97
65,300
32
4/10/97
32,100
147
4/30/97
26,500
61
6/3/97
16,100
20
6/25/97
19,700
41
7/31/97
39,800
126
8/28/97
12,400
607
10/15/97
25,500
157
11/20/97
13,400
613
12/18/97
7,920
4
1/12/98
72,300
249
2/19/98
80,000
990
3/24/98
61,700
18,800
4/13/98
20,200
1,010
4/28/98
22,100
33
5/26/98
26,800
10
6/29/98
9,810
284
7/29/98
16,700
8
8/27/98
107,000
12
9/30/98
12,300
95
11/23/98
12,700
60
12/21/98
10,400
29
1/20/99
4,200
32
68
Table A-2.
Air Stripper Performance Data for MTBE at Somersworth, New Hampshire
Date
Flow
(gallons)
Influent
(µg/L)
Midfluent
(µg/L)
Effluent
(µg/L)
3/1/99
945
18
4/5/99
1,660
36
5/4/99
1,040
<2.0
6/2/99
1,400
22
7/7/99
1,100
<10.0
8/4/99
700
<5.0
8/11/99
2,400
<5.0
8/18/99
2,900
<5.0
8/25/99
3,000
41
8/31/99
8,800
<5.0
9/29/99
1,800
<5.0
10/27/99
540
<5.0
11/30/99
520
<5.0
12/28/99
470
<5.0
1/27/00
210
<5.0
2/28/00
230
<5.0
3/30/00
130
<5.0
NA = Not available.
Table A-3.
Air Stripper Performance Data for MTBE at Culver City, California
Trial #
Influent
(µg/L)
Effluent S1
(µg/L)
%
Removal
Effluent S2
(µg/L)
%
Removal
1
3,818
8.4
99.78
1.4
99.96
2
2,400
<1.2
99.95
<1.2
99.95
3
5,100
1.3
99.97
1.1
99.98
4
3,100
<1.2
99.96
<1.2
99.96
5
3,200
1.3
99.96
1.5
99.95
6
2,500
<1.2
99.95
<1.2
99.95
69
Table A-4a.
Air Stripper Performance Data for MTBE at Bridgeport, Connecticut
Date
Influent
(µg/L)
Effluent
S1
(µg/L)
Percent
Removal
S1
Effluent
S2
(µg/L)
Percent
Removal
S2
Overall
Percent
Removal
4/1/95
2,400,000
3,100
99.87
50
98.39
99.998
5/1/95
1,100,000
14,000
98.73
50
99.64
99.995
6/1/95
1,100,000
2,700
99.75
50
98.15
99.995
7/1/95
960,000
1,100
99.89
50
95.45
99.995
8/1/95
630,000
90
99.99
50
44.44
99.992
9/1/95
360,000
150
99.96
50
66.67
99.986
10/1/95
490,000
160
99.97
50
68.75
99.990
11/1/95
480,000
250
99.95
50
80.00
99.990
12/1/95
480,000
3,500
99.27
100
97.14
99.979
2/1/96
580,000
1,400
99.76
50
96.43
99.991
3/1/96
200,000
6,600
96.70
200
96.97
99.900
Table A-4b.
Air Stripper Performance Data for BTEX at Bridgeport, Connecticut
Date
Influent
(µg/L)
Effluent
S1
(µg/L)
Percent
Removal
S1
Effluent
S2
(µg/L)
Percent
Removal
S2
Overall
Percent
Removal
4/1/95
34,000
50
99.853
10
80.000
99.971
5/1/95
14,550
10
99.931
10
0.000
99.931
6/1/95
26,900
60
99.777
20
66.667
99.926
7/1/95
22,620
70
99.691
20
71.429
99.912
8/1/95
18,500
30
99.838
20
33.333
99.892
9/1/95
10,970
10
99.909
10
0.000
99.909
10/1/95
20,990
10
99.952
10
0.000
99.952
11/1/95
15,930
10
99.937
10
0.000
99.937
12/1/95
19,260
30
99.844
10
66.667
99.948
2/1/96
16,470
10
99.939
10
0.000
99.939
3/1/96
15,140
30
99.802
10
66.667
99.934
70
Table A-5.
Air Stripper Performance Data for MTBE at Rockaway Township, New Jersey
Date
Influent
(µg/L)
Effluent
(µg/L)
Efficiency
(%)
9/3/97
10.68
1.70
84
9/10/97
6.11
1.20
80
9/17/97
7.20
1.00
86
9/24/97
11.38
1.50
87
10/1/97
9.28
1.20
87
10/8/97
6.54
1.10
83
10/15/97
6.40
0.60
91
10/24/97
3.90
0.80
79
10/29/97
4.20
1.60
62
11/5/97
1.40
<0.5
64
11/12/97
1.60
<0.5
69
11/26/97
1.06
0.60
43
12/3/97
1.20
<0.5
58
12/24/97
0.80
<0.5
38
12/31/97
0.80
<0.5
38
1/14/98
0.70
<0.5
29
1/21/98
1.40
<0.5
64
1/28/98
3.50
0.90
74
2/4/98
1.60
0.60
63
2/18/98
1.10
0.80
27
2/25/98
2.00
<0.5
75
3/4/98
1.18
<0.5
58
3/11/98
0.90
<0.5
44
3/18/98
1.20
<0.5
58
3/25/98
1.12
0.80
28
4/1/98
2.10
0.70
67
4/8/98
1.32
0.90
32
4/15/98
1.38
1.20
13
4/22/98
0.90
<0.5
44
4/29/98
0.80
<0.5
38
5/6/98
0.77
<0.5
35
5/13/98
0.80
<0.5
38
5/20/98
0.60
<0.5
17
6/3/98
0.80
<0.5
38
7/1/98
0.60
<0.5
17
8/19/98
1.70
<0.5
71
71
Table A-5.
Air Stripper Performance Data for MTBE at Rockaway Township, New Jersey
Date
Influent
(µg/L)
Effluent
(µg/L)
Efficiency
(%)
9/2/98
5.00
2.00
60
10/14/98
6.90
1.20
83
10/21/98
4.70
0.90
81
10/28/98
2.70
0.60
78
11/4/98
1.60
0.80
50
11/18/98
1.19
<0.5
58
11/25/98
0.93
<0.5
46
12/30/98
<0.5
<0.5
0
2/24/99
<0.5
<0.5
0
5/6/99
<0.5
<0.5
0
5/20/99
<0.5
<0.5
0
6/3/99
<0.5
<0.5
0
6/17/99
<0.5
<0.5
0
7/1/99
1.14
<0.5
56
7/15/99
0.90
<0.5
44
7/29/99
1.09
<0.5
54
8/12/99
0.98
<0.5
49
8/26/99
<0.5
<0.5
0
9/23/99
0.95
<0.5
47
10/6/99
0.88
<0.5
43
10/21/99
0.85
<0.5
41
11/4/99
1.13
<0.5
56
11/18/99
0.89
<0.5
44
12/1/99
<0.5
<0.5
0
12/16/99
1.32
<0.5
62
12/30/99
0.65
<0.5
23
1/6/00
1.05
<0.5
52
1/13/00
1.01
<0.5
50
1/27/00
0.85
<0.5
41
2/3/00
1.02
<0.5
51
2/10/00
0.96
<0.5
48
3/7/00
<0.5
<0.5
0
3/21/00
<0.5
<0.5
0
72
Table A-6.
Off-Gas System Performance Data for MTBE at Elmira, California
Date
Influent (ppmv)
Effluent (ppmv)
2/17/00
393
0
2/17/00
294
0
2/17/00
243
0
3/15/00
102
0
3/15/00
83
0
3/14/00
95
0.5
3/14/00
94
0.5
3/14/00
102
0
3/14/00
65
0
3/14/00
96
0
3/14/00
105
0
3/20/00
160
1
3/22/00
120
14
3/24/00
140
0
3/29/00
140
0
4/3/00
110
0
4/5/00
140
0
4/7/00
150
0
4/12/00
160
0
4/26/00
173
0
73
Appendix B
Table B-1.
Modeling Data Comparison for Low Profile Air Stripper at Somersworth, New Hampshire
Date
Influent
(µg/L)
Effluent
(µg/L)
Case 11
(µg/L)
Case 21
(µg/L)
Case 31
(µg/L)
Case 41
(µg/L)
Case 51
(µg/L)
Case 61
(µg/L)
11/22/96
988000
<5.0
0.02-0.08
0.44-1.18
0.23-0.66
2.64-6.32
1.48-3.69
0.92-2.36
11/23/96
1290000
<5.0
0.03-0.1
0.57-1.54
0.31-0.86
3.45-8.26
1.94-4.82
1.20-3.08
11/24/96
886000
<5.0
0.02-0.07
0.39-1.06
0.21-0.59
2.37-5.67
1.33-3.31
0.82-2.12
11/27/96
1670000
<5.0
0.04-0.14
0.74-1.99
0.40-1.12
4.47-10.7
2.51-6.24
1.55-3.99
12/04/96
694000
<5.0
0.02-0.06
0.31-0.83
0.16-0.46
1.86-4.44
1.04-2.59
0.65-1.66
12/12/96
129000
149
0-0.01
0.06-0.15
0.03-0.09
0.35-0.83
0.19-0.48
0.12-0.31
12/16/96
412000
388
0.01-0.03
0.18-0.49
0.10-0.28
1.10-2.64
0.62-1.54
0.38-0.98
12/23/96
322000
14.8
0.01-0.03
0.14-0.38
0.08-0.22
0.86-2.06
0.48-1.20
0.30-0.77
12/30/96
305000
14.8
0.01-0.02
0.13-0.36
0.07-0.20
0.82-1.95
0.46-1.14
0.28-0.73
01/08/97
380000
13.4
0.01-0.03
0.17-0.45
0.09-0.25
1.02-2.43
0.57-1.42
0.35-0.91
02/04/97
1240000
<2.0
0.03-0.10
0.55-1.48
0.29-0.83
3.32-7.94
1.86-4.64
1.15-2.96
02/28/97
65300
31.9
0-0.01
0.03-0.08
0.02-0.04
0.17-0.42
0.10-0.24
0.06-0.16
04/10/97
32100
147
0
0.01-0.04
0.01-0.02
0.09-0.21
0.05-0.12
0.03-0.08
04/30/97
26500
61.2
0
0.01-0.03
0.01-0.02
0.07-0.17
0.04-0.10
0.02-0.06
06/03/97
16100
20
0
0.01-0.02
0-0.01
0.04-0.10
0.02-0.06
0.01-0.04
06/25/97
19700
41.3
0
0.01-0.02
0-0.01
0.05-0.13
0.03-0.07
0.02-0.05
07/31/97
39800
126
0
0.02-0.05
0.01-0.03
0.11-0.25
0.06-0.15
0.04-0.10
08/28/97
12400
607
0
0.01
0-0.01
0.03-0.08
0.02-0.05
0.01-0.03
10/15/97
25500
157
0
0.01-0.03
0.01-0.02
0.07-0.16
0.04-0.10
0.02-0.06
11/20/97
13400
613
0
0.01-0.02
0-0.01
0.04-0.09
0.02-0.05
0.01-0.03
12/18/97
7920
4.3
0
0
0-0.01
0.02-0.05
0.01-0.03
0.01-0.02
01/12/98
72300
249
0-0.01
0.03-0.09
0.02-0.05
0.19-0.46
0.11-0.27
0.07-0.17
02/19/98
80000
990
0-0.01
0.04-0.10
0.02-0.05
0.21-0.51
0.12-0.30
0.07-0.19
03/24/98
61700
18800
0-0.01
0.03-0.07
0.01-0.04
0.17-0.39
0.09-0.23
0.06-0.15
04/13/98
20200
1010
0
0.01-0.02
0-0.01
0.05-0.13
0.03-0.08
0.02-0.05
04/28/98
22100
33.4
0
0.01-0.03
0.01
0.06-0.14
0.03-0.08
0.02-0.05
05/26/98
26800
9.8
0
0.01-0.03
0.01-0.02
0.07-0.17
0.04-0.10
0.02-0.05
06/29/98
9810
284
0
0-0.01
0-0.01
0.03-0.06
0.01-0.04
0.01-0.02
07/29/98
16700
8
0
0.01-0.02
0-0.01
0.04-0.11
0.03-0.06
0.02-0.04
08/27/98
107000
11.5
0
0.05-0.13
0.03-0.07
0.29-0.68
0.16-0.40
0.10-0.26
09/30/98
12300
94.9
0
0.01
0-0.01
0.03-0.08
0.02-0.05
0.01-0.03
1Data
for all six cases ranges for 66 to 70°F.
74
Table B-1.
Modeling Data Comparison for Low Profile Air Stripper at Somersworth, New Hampshire
Date
Influent
(µg/L)
Effluent
(µg/L)
Case 11
(µg/L)
Case 21
(µg/L)
Case 31
(µg/L)
Case 41
(µg/L)
Case 51
(µg/L)
Case 61
(µg/L)
11/23/98
12700
59.7
0
0.01-0.02
0-0.01
0.03-0.08
0.02-0.05
0.01-0.03
12/21/98
10400
28.9
0
0-0.01
0-0.01
0.03-0.07
0.02-0.04
0.01-0.02
01/20/99
4200
32.2
0
0-0.01
0
0.01-0.03
0.01-0.02
0-0.01
03/01/99
945
17.8
0
0
0
0-0.01
0
0
04/05/99
1660
36.2
0
0
0
0-0.01
0-0.01
0
05/04/99
1040
<2.0
0
0
0
0-0.01
0
0
06/02/99
1400
22
0
0
0
0-0.01
0-0.01
0
07/07/99
1100
<10.0
0
0
0
0-0.01
0
0
08/04/99
700
<5.0
0
0
0
0
0
0
08/11/99
2400
<5.0
0
0
0
0.01-0.02
0-0.01
0-0.01
08/18/99
2900
<5.0
0
0
0
0.01-0.02
0-0.01
0-0.01
08/25/99
3000
41
0
0
0
0.01-0.02
0-0.01
0-0.01
08/31/99
8800
<5.0
0
0
0-0.01
0.02-0.06
0.01-0.03
0.01-0.02
09/29/99
1800
<5.0
0
0
0
0-0.01
0-0.01
0
10/27/99
540
<5.0
0
0
0
0
0
0
11/30/99
520
<5.0
0
0
0
0
0
0
12/28/99
470
<5.0
0
0
0
0
0
0
01/27/00
210
<5.0
0
0
0
0
0
0
02/28/00
230
<5.0
0
0
0
0
0
0
03/30/00
130
<5.0
0
0
0
0
0
0
1Data
for all six cases ranges for 66 to 70°F.
75
Table B-2.
Modeling Data Comparison for Packed Water Air Stripper at LaCrosse, Kansas
(Water Flow Rate = 480 gpm, Air-to-Water Ratio = 156)
Actual
Influent
(µg/L)
Actual
Effluent
1st Tower
(µg/L)
ASAPTM
Influent
at 60°F
(µg/L)
ASAPTM
Effluent
at 70°F
(µg/L)
Actual
Effluent
2nd Tower
(µg/L)
ASAPTM
Effluent
at 60°F
(µg/L)
ASAPTM
Effluent
at 70°F
(µg/L)
136
14.3
1.303
0.407
ND
0.137
0.0428
107
11.4
1.03
0.32
ND
0.109
0.0341
115
ND
1.10
0.344
ND
—
—
46.1
14.9
0.442
0.138
ND
0.143
0.0445
129
11
1.24
0.386
ND
0.105
0.386
140
14
1.34
0.418
ND
0.134
0.0419
52.6
13.1
0.504
0.157
3.33
0.125
0.0392
954
168
9.14
2.85
29.4
1.61
0.502
159
35.1
1.52
0.475
19.3
0.336
0.105
197
51.4
1.89
0.589
NA
0.492
0.154
93.9
17.9
0.899
0.281
4.02
0.171
0.0535
125
23.9
1.197
0.374
5.01
0.229
0.0714
290
171
2.78
0.867
51.1
1.638
0.511
973
220
9.32
2.91
51.4
2.107
0.658
71.8
15.8
0.688
0.215
3.92
0.151
0.0472
98.5
20
0.944
0.294
4.75
0.192
0.0598
93.2
19
0.893
0.279
2.99
0.182
0.0568
85.1
18
0.815
0.254
4.05
0.172
0.0538
ND = Non-detect.
NA = Not available.
76
Table B-3.
Modeling Data Comparison for Packed Water Air Stripper at LaCrosse, Kansas
(Water Flow Rate = 350 gpm, Air-to-Water Ratio = 214)
Actual
Influent
(µg/L)
Actual
Effluent
1st Tower
(µg/L)
ASAPTM
Influent
at 60°F
(µg/L)
ASAPTM
Effluent
at 70°F
(µg/L)
Actual
Effluent
2nd Tower
(µg/L)
ASAPTM
Effluent
at 60°F
(µg/L)
ASAPTM
Effluent
at 70°F
(µg/L)
136
14.3
0.627
0.170
ND
0.0659
0.0179
107
11.4
0.493
0.134
ND
0.0525
0.0142
115
ND
0.530
0.144
ND
—
—
46.1
14.9
0.212
0.0575
ND
0.0687
0.0186
129
11
0.594
0.161
ND
0.0507
0.0137
140
14
0.645
0.175
ND
0.0645
0.0175
52.6
13.1
0.242
0.0657
3.33
0.0604
0.0164
954
168
4.40
1.19
29.4
0.774
0.210
159
35.1
0.733
0.198
19.3
0.162
0.0438
197
51.4
0.908
0.246
NA
0.237
0.0642
93.9
17.9
0.433
0.117
4.02
0.0825
0.0223
125
23.9
0.576
0.156
5.01
0.110
0.0298
290
171
1.34
0.362
51.1
0.788
0.213
973
220
4.48
1.22
51.4
1.014
0.275
71.8
15.8
0.331
0.896
3.92
0.0728
0.0197
98.5
20
0.454
0.123
4.75
0.0922
0.0250
93.2
19
0.429
0.116
2.99
0.0875
0.0237
85.1
18
0.392
0.106
4.05
0.0829
0.0225
ND: Non-detect (<0.5 µg/L).
NA = Not available.
77
Table B-4.
Modeling Data Comparison for Low Profile Air Stripper at Culver City, California
Date
Influent
(µg/L)
Effluent from
S-01 (µg/L)
ASAPTM
Effluent at 70°F
(µg/L)
11/10/99
17,000
NA
0.205
11/15/99
3,818
8.4
0.0460
12/20/99
6,300
NA
0.0758
12/21/99
2,400
NA
0.0289
01/13/00
4,500
NA
0.0542
01/21/00
5,100
1.3
0.0614
02/01/00
4,200
1.1
0.0506
02/12/00
3,000
ND
0.0361
02/16/00
3,200
1.3
0.0385
02/25/00
3,000
ND
0.0361
03/01/00
2,500
ND
0.0301
03/09/00
2,900
ND
0.0349
03/15/00
4,100
ND
0.0494
ND = Non-detect.
NA = Not available.
78
Table B-5.
Modeling Data Comparison for Low Profile Air Stripper at Rockaway Township, New Jersey
Date
Influent
(µg/L)
Effluent
(µg/L)
ASAPTM
Effluent at 50°F
(µg/L)
ASAPTM
Effluent at 55°F
(µg/L)
10/15/97
6.4
0.6
0.40
0.27
10/24/97
3.9
0.8
0.24
0.17
10/29/97
4.2
1.6
0.26
0.18
11/05/97
1.4
0.5
0.087
0.059
11/12/97
1.6
0.5
0.10
0.068
11/26/97
0.7
0.6
0.044
0.030
12/10/97
0.8
1
0.050
0.034
01/07/98
0.7
1.3
0.044
0.030
01/14/98
0.7
0.5
0.044
0.030
01/28/98
3.5
0.9
0.22
0.015
02/04/98
1.6
0.6
0.10
0.068
02/11/98
1.7
1.8
0.11
0.072
02/18/98
1.1
0.8
0.069
0.047
03/25/98
0.7
0.8
0.044
0.030
04/01/98
2.1
0.7
0.13
0.089
04/08/98
0.8
0.9
0.050
0.034
04/15/98
0.8
1.2
0.050
0.034
10/14/98
6.9
1.2
0.43
0.29
10/21/98
4.7
0.9
0.29
0.20
10/28/98
2.7
0.6
0.17
0.16
11/04/98
1.6
0.8
0.10
0.068
10/06/99
0.88
<0.5
0.055
0.055
10/21/99
1.1
<0.5
0.069
0.069
11/04/99
1.13
<0.5
0.070
0.070
11/18/99
0.89
<0.5
0.055
0.055
12/16/99
1.32
<0.5
0.082
0.082
12/30/99
1.4
<0.5
0.088
0.087
01/06/00
1.21
<0.5
0.075
0.075
01/13/00
1.32
<0.5
0.082
0.082
01/27/00
1.32
<0.5
0.082
0.082
02/03/00
1.88
<0.5
0.12
0.12
02/10/00
1.43
<0.5
0.089
0.089
03/07/00
0.5
<0.5
0.031
0.031
03/21/00
0.6
<0.5
0.097
0.037
79
80

Removal of MTBE from Drinking Water Using Air Stripping: Case

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