Experience from Start-up and Operation ... Plants, and Testing of a New Deammonification IFAS Configuration

Experience from Start-up and Operation ... Plants, and Testing of a New Deammonification IFAS Configuration

Experience from Start-up and Operation of Deammonification MBBR
Plants, and Testing of a New Deammonification IFAS Configuration
R. Lemaire1, M. Christensson2, H. Zhao3, M. Le Noir2, C. Voon4
1
Veolia Water Technical Department, 1 rue Giovanni Battista Pirelli, 94417 St-Maurice, France
AnoxKaldnes AB, Klosterängsvägen 11A, 226 47 Lund, Sweden
3
Kruger Inc., 4001 Weston Parkway, Cary, NC 27513, USA
4
Veolia Water Solutions and Technologies Australia, Bay Centre, 65 Pirrama Road, Pyrmont NSW 2009
2
Abstract
A single-stage deammonification process utilizing biofilms on moving carriers in a mixed reactor
(ANITA™ Mox) is studied. Partial nitritation and autotrophic N-removal occur simultaneously
within the biofilm, where aerobic and anoxic zones result from oxygen mass transfer limitation.
Ammonium Oxidizing Bacteria (AOB) oxidize NH4 to NO2 in the aerobic zone of the biofilm (i.e.
external biofilm) while Anammox bacteria (AnAOB) located in the anoxic zone of the biofilm (i.e.
internal biofilm) consume NO2 produced by AOB together with the excess NH 4. The process has
been implemented at full-scale as a Moving Bed Biofilm Reactor (MBBR) to treat reject water from
dewatering of digested sludge. Startup of these installations was accelerated using a seeding strategy
whereby 3-15% of carriers with established AOB/AnAOB biofilm were mixed with new carriers. Nremoval rates up to 1.2 kgN/m3react.d have been observed in the full-scale process. The achievable
rate is influenced by substrate transport inside the biofilm, which depends on factors such as biofilm
density, thickness, temperature, and substrate concentrations. One possible strategy to increase the
N-removal is to enhance substrate transport. Using Integrated Fixed-Film Activate Sludge (IFAS) to
separate the nitritation and anammox reactions spatially, instead of adjacent in the same biofilm,
allows the AOB to grow in suspended phase to better utilize DO, while allowing the biofilm to
specialize in AnAOB reaction to achieve higher rates. A lower bulk DO can be used in this mode.
Results from full-scale ANITA Mox MBBR treating sidestream effluent are presented together with
preliminary ANITA Mox IFAS results from a 50m3 full-scale prototype showing an increase in Nremoval rate of up to 3 times that usually achieved in pure MBBR configuration.
Keywords:
Anammox, ANITA Mox, IFAS, MBBR, Nitrogen removal, Sidestream treatment
INTRODUCTION
Energy consumption is often a large component in the total operation costs of a wastewater
treatment plant (WWTP). In the quest for self-sufficient or even energy-positive WWTPs, anaerobic
digestion of primary and secondary sludge is a key element. It is, therefore, important to separate
particulate organic matter from incoming raw wastewater, which can then be partially transformed
into biogas through anaerobic digestion and converted into energy by combined heat and power
(CHP) units. Every action taken towards improving the anaerobic digestion performance - such as
sludge thickening and pre-treatment by mechanical disintegration or thermal hydrolysis, better
digester operation (mixing and continuous feeding), co-digestion of biowastes and other cosubstrates - will bring the WWTP a step closer to self-sufficiency (Chudoba et al., 2010).
Such improvements on the anaerobic transformation of organic matter from primary and secondary
sludge to biogas can result in higher nitrogen levels in the sidestream reject water that is recycled to
the inlet of the WWTP and can constitute up to 20-30% of the total N load. In order to address both
WWTP treatment efficiency (i.e. quality of treated effluent) and energy savings, this increased
nitrogen load has to be removed without further increasing the energy consumption of the plant.
Costly expansion of the aeration capacity and reactor volume together with increased consumption
of external carbon source should also to be avoided.
Dedicated sidestream treatment can be a long-term solution to this situation, especially when
considering energy- and cost-effective autotrophic N-removal processes using anammox bacteria.
Due to the slow growth rate of anammox bacteria, long sludge ages have to be maintained, meaning
that most of the current autotrophic N-removal processes are biofilm systems, with or without
support material, operated as 2-stage systems, such as combined SHARON / Anammox-granular
process (Abma et al., 2007) or 1-stage systems, also referred to as the “Deammonification” process,
such as granular Sequencing Batch Reactors (SBR) (Wett, 2007; Vlaeminck et al., 2008; VazquezPadin et al., 2009) or Moving-Bed Biofilm Reactors (MBBR) (Rosenwinkel and Cornelius, 2005;
Cema, 2009).
Difficulty controlling the coupling between the predominant nitritation activity of flocular sludge
and the predominant anammox activity of the granular sludge have been reported with 1-stage
granular deammonification systems (Wett, 2010; Vlaeminck, 2008). Granule flotation has also been
reported in highly-loaded anammox granular systems, causing wash-out of anammox granules and
the deterioration of the process performance (Chen, 2010). Issues related to high levels of TSS in
the reject water have also been reported with granular systems causing the loss of N-removal
activity and the need to re-seed the system (Lindell and Heinonen, 2013).
Alternatively, MBBR is seen as a robust biofilm technology to perform 1-stage deammonification
where ammonium oxidizing bacteria (AOB) and anammox bacteria are maintained in a biofilm on
suspended MBBR carriers with no risk of biomass wash-out (Cema, 2009). MBBR systems are less
sensitive to incoming TSS, since solids tend wash through the non-clogging sieves (flow-through
system) while carriers with anammox biomass are retained in the MBBR.
In this paper, we present full-scale results for the MBBR deammonification process called
ANITA Mox implemented in 4 plants in Europe (Sjölunda, Växjö – Sweden; Holbæk, Grindsted
– Denmark) with three more in start-up/design/construction in the US (James River WWTP in
Newport News, VA, South Durham WPCF in Durham, NC and Eagan WRP in Chicago, IL) for
sidestream treatment. Detailed performances and design parameters of the operating full-scale
plants together with the strategy developed for a quick start-up and overall energy efficiency
through advanced aeration control strategy are presented.
Results of a new IFAS ANITA Mox process recently tested at Sjölunda WWTP in Malmö, Sweden
are also presented.
Presentation of the ANITA Mox process
ANITA Mox is a 1-stage MBBR deammonification process. Partial nitrification to nitrite and
autotrophic N-removal (i.e. anammox) occur simultaneously within the biofilm. Aerobic and
anoxic zones reside adjacent to each other due to oxygen mass transfer limitation under limited bulk
DO concentration. The biological processes taking place inside the biofilm are illustrated in Figure
1. AOB oxidize NH4 to NO2 in the aerobic zone of the biofilm (i.e. outer part) while anammox
bacteria located in the anoxic zone of the biofilm (i.e. inner part) consume NO2 produced by AOB
together with the residual NH4.
NH4+
Liquid
N2
Nitritation
AOB
NO2
Anammox
Biofilm
Carrier
-
O2
Aerobic
Anoxic
Figure 1. Schematic of 1-stage nitritation/anammox biological processes occurring inside a
carrier’s biofilm.
The use of large-surface-area AnoxKaldnes carrier material, shown in Figure 2, allows for compact
design and simple process operation with very high biomass retention ability through the use of
non-clogging sieves.
Figure 2. BiofilmChip™ M (1200 m2/m3), K3 (500 m2/m3) and Anox™ K5 (800 m2/m3) colonised
ANITA Mox biofilm carriers.
Real-time DO control strategy. An aeration control system has been developed and implemented on
ANITA Mox MBBR reactors. The strategy avoids unwanted oxidation of NO2 into NO3 by nitrite
oxidizing bacteria (NOB) in the aerobic zone of the biofilm maximizing the amount of nitrite
available for the anammox bacteria. The DO setpoint is automatically adjusted based on online inlet
and outlet concentrations of NH4 and NO3 to control the NO3 production below 11% of NH4
removed (i.e. stoichiometric NO3 production by anammox) while keeping high NH4 oxidation
performance in the reactor. This real-time DO control strategy reduces the need of mechanical
mixer in the MBBR due to the continuous aeration pattern.
Strategy to Reduce Start-up time. The very slow growth of anammox bacteria and sensitivity
towards high concentrations of oxygen, nitrite/free nitrous acid and free ammonia during the startup phase result in prolonged biological startup when growing the organisms from scratch. To
shorten the start-up phase, new ANITA Mox processes are seeded with a small fraction of colonized
carriers, which reduce the time required for the development of a mature deammonification biofilm
on the new carriers. The concept of seeding has proven to significantly decrease the start-up time
from around a year to 2-3 months, depending of the amount of seeding (Lemaire et al., 2011) and
are in contradiction with recent studies by Schneider et al. (2009) reporting that seeding with fully
functional deammonification biofilm was not an efficient start-up strategy for MBBR
deammonification systems. To meet the request for seeding carriers, the ANITA Mox full-scale
plant built in 2010 at Sjölunda WWTP is used as a nursery for anammox bacteria growing on
suspended carriers, referred to as the “BioFarm”. The ANITA Mox unit that is in design at the
South Durham WPCF (NC, USA) will also serve as a “BioFarm” to seed future ANITA Mox plants
in the North America region.
Description of Sjölunda WWTP facilities
Sjölunda WWTP (550,000 PE) has a total capacity of 40 tBOD7/d and a Qmax of 4.4 m3/s on the
biological treatment system. The current configuration of the WWTP (Figure 3) is as follows: pretreatment followed by primary settlers (particulate BOD removal), high rate activated sludge (BOD
removal) with clarifiers, revamped trickling filters (nitrification), MBBR (post denitrification) and
DAF. Thickened primary sludge and biological sludge are mixed and sent to 6 anaerobic digesters
(16,000m3, 20d HRT, 35°C). Digested sludge is dewatered continuously by 3 centrifuges operated
50% of the time. Approximately 50% of the reject water flow is treated by an existing SBR
(1920m3) operated in nitritation mode only while the remaining 50% (i.e. around 300 kgN/d) is now
treated by the ANITA Mox system (200m3).
Pre-treatment
High rate AS
Bio-Sludge Thickener
Nitrifying
Trickling
Filters
DAF
Post DN
MBBR
Anaerobic
Digesters
Gravity
Thickener
Centrifuges
Nitritation SBR
40% reject
water flow
ANITATM Mox
MBBR
Figure 3. Layout of Sjölunda WWTP in Malmö, Sweden. Adapted from Mases et al. (2010).
Description of Sundet WWTP facilities
Sundet WWTP in Växjö (Sweden) is designed for 80,000 PE, including industrial wastewater of
approximately 1200 kgBOD/d. The current configuration of the WWTP (Figure 4) is as follows:
pre-treatment followed by 6 parallel lines including a primary settling with chemical addition, an
activated sludge treatment for BOD and N-removal with clarifiers and a tertiary sand filtration unit.
The treated wastewater is then discharged to the lake Norra Bergunda. Thickened primary and
biological sludge, as well as sludge from other smaller WWTPs, are digested to two mesophilic
digesters, before being dewatered in centrifuges. The reject water is now treated in an ANITA Mox
reactor before being sent back to the inlet of the WWTP. The ANITA Mox is designed to treat 320
kgN/d and will be upgraded in the future to treat up to 430 kgN/d when food residuals will be codigested, sanitized and digested a second time in a newly built digester.
Inlet
Grit and grease
removal
Primary settling
Biological treatment
Gas holder
Sludge
thickening
Digester
Clarifier
Tertiary
filtration
Lake
CHP unit
Centrifuges
Landspreading
ANITA Mox
Figure 4. Layout of Sundet WWTP in Växjö, Sweden.
Description of Holbaek WWTP facilities
Holbæk WWTP is designed for 60,000 PE (3,670 kgBOD/d) treating the wastewater from several
neighboring municipalities. About 90-95% of the total inlet of the plant is municipal waste water
with a 5-10% fraction from industries. Preliminary treatment consists of screens and sand-grease
removal before the primary sedimentation tanks. Biological treatment takes place in a group of 6
Sequencing Batch Reactors (SBRs). Sludge is treated in an anaerobic digester. Iron sulfate is used
for P removal. The treated water is discharged to the sea with the following effluent limits: BOD 15
mg/l; TN 4 mg/l summer and 6 mg/l in winter; and TP 1 mg/l.
Digested sludge is dewatered through a filter press, producing reject water in batches. A 50 m 3
equalization tank allows the ANITA Mox reactor to receive a relatively constant rate of 10 m 3/h
with a designed capacity of 120 kgN/day (i.e. including both reject water and leachate). The process
was built reusing an existing 600 m3 tank which allows for some spare volume and a design at 2021 C. The lower-than-normal temperature is due to the need of treating leachate from a nearby
landfill.
Description of Grindsted WWTP facilities
Grindsted WWTP is designed for 70,000 PE (4,200 kgBOD/d). Water-intensive industries, such as
slaughterhouses, which are connected to the municipal sewer account for close to 2/3 of the WWTP
BOD and TN load. The incoming wastewater is screened for sand and grease removal while the
BOD and N are removed biologically in a BIODENITRO process. Phosphorous is removed by coprecipitation in the BIODENITRO tank. The treated water is discharged to a nearby watercourse
with the following effluent limits: BOD 10 mg/l; TN 8 mg/l and TP 1.5 mg/l.
The origin of the solids sent to a BioPasteur® digester with a 247 kW CHP unit is 45% primary and
secondary WWTP sludge, 35% organic household waste and 20% organic industrial waste. Reject
water from the downstream screw press is then treated in a 140m3 ANITA Mox reactor design for
100 kgN/d.
MATERIALS AND METHODS
Design parameters of Full-scale ANITA Mox plants
The reject water composition and sludge dewatering operation at Sjölunda, Sundet, Holbaek and
Grinsted WWTP are detailed in Table 1 while the main design and operating parameters of the fullscale ANITA Mox reactors are presented in Table 2.
Table 1. Reject Water characteristics at Sjölunda, Sundet, Holbaek and Grindsted WWTP.
Characteristics
Units
Sjölunda
Sundet
Holbæk
Type of sludge digested
--
primary +
secondary
primary +
secondary +
food waste
primary +
secondary
Total flow – mean
NH4 – mean (# sample)
TKN – mean (# sample)
CODs – mean (# sample)
BOD7 – mean (# sample)
HCO3- – mean (# sample)
TSS – mean (# sample)
m3/d
mgN/L
mgN/L
mg/L
mg/L
mg/L
mgSS/L
650
906 (420)
1041 (48)
288 (81)
185 (69)
4,570 (57)
859 (132)
160
851 (92)
914 (92)
--4,650 (16)
513 (92)
125
833 (72)
------
Grindsted
primary +
secondary +
food waste +
industrialwaste
125
1221 (30)
------
Table 2. Design and operating parameters of full-scale ANITA Mox MBBRs
Parameters
Effluent
Sjölunda WWTP
Municipal reject water Municipal reject water
Volume
4 x 50m3 (=200m3)
Design N-load
200 kgN/d
Carrier type
Temperature
K3 / K5 / BioChipM
22-34°C (no control)
0.5-1.5 mgO2/L
Advanced DO control
strategy
Continuous aeration
(Coarse bubbles)
August 2010
DO
Aeration
Start-up
Sundet WWTP
300m3 (existing tank)
320 kgN/d (1st phase)
430 kgN/d (2nd phase)
Anox K5
26-34°C (no control)
0.5-1.5 mgO2/L
Advanced DO control
strategy
Continuous aeration
(Fine bubbles)
December 2011
Holbæk WWTP
Mix reject water /
landfill leachate
600m3 (existing tank)
Grindsted WWTP
Co-digestion reject
water
140m3 (new tank)
120 kgN/d
100 kgN/d
Anox K3
15-30°C (no control)
0.5-1.5 mgO2/L
Advanced DO control
strategy
Continuous aeration
(Coarse bubbles)
May 2012
Anox K5
25-35°C (no control)
0.5-1.5 mgO2/L
Advanced DO control
strategy
Continuous aeration
(Coarse bubbles)
July 2013
ANITA Mox at Sjölunda WWTP. This full-scale unit was made of 4 parallel 50m3 and 6m deep
reactors in order to test different carrier filling degree (from 40-50%) and different types of
AnoxKaldnes carrier media (Table 2). This plant is also used as “BioFarm” to provide some seeded
carriers to shorten the start-up phase of other full-scale ANITA Mox plant. NH4, NO3 (WTW),
temperature and pH (Endress+Hausser) are measured on-line in the reject water feed and inside
each reactor. Airflow and DO (Endress+Hausser) are also measured and controlled in each reactor.
ANITA Mox at Sundet WWTP. This second full-scale plant consists of a single 300m3 covered
reactor. It is a refurbished 3m deep SBR, using the existing fine-bubble aeration system (Table 2).
To meet future N-load increases, the reactor design was made very flexible with possibilities to
upgrade the treatment capacity by increasing the carriers filling degree to match the increase reject
water load expected in the future (addition of co-waste in the digester). The plant is using the Anox
K5 carrier with a protected surface of 800 m2/m3 as shown in Figure 2. NH4, NO3 (WTW),
temperature and pH (Endress+Hausser) are measured on-line in the MBBR together with NH4
(WTW) in the incoming reject water. Airflow and DO (Endress+Hausser) are also measured and
controlled in the reactor.
ANITA Mox at Holbæk WWTP. An existing 600m3 reactor was converted into an ANITA Mox
MBBR to treat a mixture of municipal sludge digestion centrate and leachate from a nearby landfill.
The design load is 120 kgN/d with a minimum temperature as low as 15°C due to the low
temperature of leachate in winter time and the relatively long HRT in the 600m3 MBBR.
ANITA Mox at Grinsted WWTP. A new 140m3 MBBR ANITA Mox reactor using AnoxK5 carriers
was built to treat the reject water from the co-digestion unit. NH4 level is rather high with value up
to 1.8 gN-NH4/L depending on the type of co-waste fed to the digester. TSS level is also quite high
at time (up to 4-5 g/L) but most incoming TSS are passing through the MBBR with limited impact
on the process performance and sent back to the head of the plant.
ANITA Mox at James River WWTP. This system is currently under start-up. It consists of one
400m3 reactor filled with Anox K5 media to treat 285 m3/d of centrate. Design influent ammonia is
890 mg/L at 30°C design temperature.
ANITA Mox at South Durham WWTP. This system is in design with an anticipated start-up in 2015.
It will consist of a two parallel 318 m3 reactors filled with Anox K5 media to treat 300 m3/d of
centrate. Design influent ammonia is 1,000 mg/L at 24°C design temperature.
ANITA Mox at Eagan WRP. This system is in construction with an estimated start-up in mid-2014.
It will consist of 4 parallel MBBR ANITA Mox (retrofit into 4 existing DAF tanks) to treat 940
kgN/d of centrate.
Analytical Method
Chemical analysis. Mixed liquor samples were filtered at 1.6 µm before analysis for NH4, NO3,
NO2 and soluble COD (Dr Lange kits, Hach Lange). TSS were analyzed according to the standard
methods (APHA, 1995).
Off gas analysis. To evaluate the N2O emissions from the ANITA Mox process, continuous off-gas
measurements have been performed during normal operation conditions at Sjölunda WWTP. Offgas was pumped continuously at 30L/h to a non-dispersive infrared analyser (VA-3000, Horiba) to
determine the N2O gas fractions (in ppmv). The flux of N2O emitted (gN-N2O/d) was calculated
considering that the outlet air flow rate (Nm3/h) was equal to the inlet air supply given by the mass
flow controller. The quantify N2O emitted from the MBBR was expressed in % of gN-N2Oemitted per
gNremoved. Four periods between 1 to 6 days long in 2011 without any major operational
disturbances or problems with the online off-gas were chosen to evaluate the N2O emissions from
the ANITA Mox process.
Energy efficiency. Energy consumption was measured on the 50 m3 MBBR equipped with Biofilm
Chip M at Sjölunda WWTP with continuous aeration and therefore no need for mechanical mixing.
The total energy consumption of the ANITA Mox was therefore only based on the energy
consumption of the blower. Three different time periods were chosen during which NH4 and NO3
level in the influent and effluent, aeration intensity and blower power consumption were
continuously monitored. The same method was applied on the ANITA Mox at Sundet WWTP once
a specific air flow meter was installed on the air supply to the MBBR tank.
Specific anammox batch tests. Maximum anammox capacity was measured in 3L reactors with N2
sparging (2 L/h) to provide mixing and maintain anoxic condition. Temperature was kept at 30°C
with a thermostat bath. A known number of carriers (typical 100 pieces) were added to a synthetic
medium containing NH4-N (25 mg/L), NO2-N (25 mg/L), PO4-P (2.5 mg/L), NaHCO3 (2 g/L) and
trace metal solution (2 ml/L). Samples were taken every 5-10 minutes and maximum N-removal
capacity was determined by plotting nitrogen concentration per surface area vs time.
RESULTS AND DISCUSSION
Performances of the ANITA Mox process at Sjölunda WWTP
Due to limitations of seeding media available and in order to optimize the start-up procedure, the 4
ANITA Mox reactors (i.e. MBBR1, MBBR2, MBBR3 and MBBR4) were started up at different
time. Table 3 summarizes the start-up conditions of MBBR1, which was started first, and MBBR4
which was the last one to be started. MBBR1 was seeded with 0.9m3 of colonized carriers coming
from a 2m3 Pilot-Plant (Lemaire et al. 2011). MBBR4 was initially started-up in Feb11 while
outside T°C were well below 0°C resulting in some issues with freezing pipes during stoppages due
to site maintenance of centrifuges. MBBR4 was re-started in Dec11 after 84% of the reactor media
(i.e. 21m3) were taken away to start up the new ANITA Mox unit at Sundet WWTP (Table 3).
Table 3. Operation conditions during start-up of MBBR1 and MBBR4 at Sjölunda WWTP
MBBR1
MBBR4
Type of media used
BiofilmChip M
Anox K5
Total filling degree
40%
50%
0.9m3 from ANITA Mox 4m3 of remaining K5 carriers
Seeding media used
Pilot Plant
after 21m3 were taking out
Seeding % of total carrier surface
3%
16%
Start-up time
August 2010
December 2011
Outdoors T°C during start-up
18°C - 20°C
-10°C - 5°C
Long-term performances of MBBR1, the first ANITA Mox full-scale reactor started up at Sjölunda
WWTP are presented in Christensson et al. (2013). NH4 level in the effluent was always below 100150 mgN-NH4/L and the ratio NO3-prod. : NH4-rem. was in the range of 8-15% which is close to
the stoichiometric ratio (i.e. 11%) if nitrate was only produced by anammox bacteria with no further
oxidation of nitrite into nitrate by NOB and no reduction of nitrate by heterotrophic denitrifiers. The
real-time DO control strategy developed for the ANITA Mox process was very successful in
limiting the activity of NOB in the system and therefore assuring that most of the nitrite produced
by the AOB is actually used by the anammox bacteria. The nitrite concentration in the outlet was
always very low (i.e. <5 mgN/L) although transitory accumulations of nitrite up to 120 mgN-NO2/L
were observed during the start-up period with no real incidence on the MBBR performances. The
fact that nitrite was barely present in the MBBR indicates that the system was likely NO2 limited
and that anammox activity was limited by the supply of NO2 from the AOB. After only 4 months
operation and with only 3% of seeding material, NH4-removal rate reached 1.2 kgN/m3react.d with
90% NH4-removal efficiency. In spite of variation in N-load the NH4-removal stayed high, typically
>90%, for the entire operation period while TN removal averaged 80%. These performances were
obtained (i) without any pre-treatment of the reject water, (ii) without any chemical addition of
methanol, acid or base solution, (iii) with no need of mechanical mixers in the MBBR (i.e.
continuous aeration strategy sufficient for mixing carriers) and (iv) without any heating system even
during the cold winter months in Sweden.
In addition to serve as a “BioFarm” nursery for rapid start-up of new ANITA Mox plant, the four
50m3 MBBR unit at Sjölunda WWTP are also used to test different operating strategies, different
type of carriers, and build-up some solid in-depth expertise for 1-stage MBBR deammonification
process. Long term operation of the ANITA Mox process at Sjölunda WWTP has proven to be a
robust and stable process towards variations in loads of reject water supply, variations in suspended
solids, power failure and pumping issues often encountered at treatment plants while still
maintaining high N-removal performances.
1200
200
1100
180
700
140
120
600
100
500
80
400
60
(a)
200
NO3 out, NO2 out (mgN/L)
800
300
NH4-load & removal rates (kgN/m3.d)
160
NH4-N in
NH4-N out
NO3-N out
NO2-N out
900
40
100
20
0
1,4
1,3
1,2
1,1
1
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0
0
31
29
27
25
NH4-N load
NH4-N rem
T°C
T°C
NH4 in/out (mgN/L)
1000
23
21
19
(b)
17
15
280 290 300 310 320 330 340 350 360 370 380 390 400 410 420 430 440
Days
Figure 5. MBBR4 performances after second start-up: NH4, NO3 and NO2 measured in inlet and
outlet (a); NH4 loading and removal rates and T°C in MBBR4 (b).
Figure 5 shows inlet and outlet concentrations, as well as N-loading and removal rate after the
second start-up of MBBR4 on Day 308 when 21m3 of Anox K5 carriers (i.e. corresponding to 84%
of the total media amount in the reactor) were taken out in order to seed the ANITA Mox reactor at
Sundet WWTP for fast start-up (Table 3). Only 4m3 of media remained in the MBBR4 reactor (i.e.
16% seeding), and another 21m3 of virgin Anox K5 carriers were added to quickly reach again
maximum removal performances. This new start-up explains the relatively high NH4 level in the
outlet (i.e. up to 300-400 mg/L) during the first 70 days after virgin media were added (Figure 5a).
After only 70 days and with only 16% initial seeded carriers remaining, NH4-removal rate in
MBBR4 reached back 1 kgN/m3react.d.
Energy Efficiency
During the 3 periods where energy consumption was measured, MBBR1 was removing between 48
and 60 kgN-NH4/d depending on the influent concentration (corresponding to between 43 and 56 kg
TN/d). The blower was operating continuously ensuring a DO in the reactors that varied between
0.5 and 1.5 mgO2/L. The average power consumption for the 3 different periods of the 50m3
ANITA Mox MBBR at Sjölunda WWTP varies between 1.45-1.75 kWh/kgN-NH4 removed. This
number is expected to vary depending on the size and the geometry of the ANITA Mox reactor. The
MBBRs used in this ANITA Mox installation were rather small (50m3 each) with a high
wall/volume surface ratio and therefore lower energy consumption can be expected for larger
MBBRs with sufficient water depth (i.e. >5m) to have good oxygen transfer rate. This energy
consumption represents only around 50-60% of the energy consumption of the nitritation SBR
treating the same reject water at Sjölunda WWTP, which is reported to be around 2.9 kWh/kgNNH4 removed (Gustavsson, 2010). Likewise, the energy consumption of this ANITA Mox plant is
much lower than what has been previously reported from other 1-stage MBBR-type Anammox
processes: 2.3 kWh/kgN-removed at Himmerfjärden WWTP in Sweden, and 5.6 kWh/kgNremoved at Hattingen WWTP in Germany, both operating as DeAmmon processes with intermittent
aeration (Gustavsson, 2010). This relatively low energy consumption in Sjölunda WWTP
demonstrates the efficiency of the aeration control strategy which adapts in real-time the aeration
intensity to the real process need.
N2O Emission
The N2O was measured in the off-gas of the MBBRs at Sjölunda WWTP during 4 separate periods
under typical operating conditions. The N2O emissions measured in the off-gas fluctuated between
0-200 ppmv with the average N2O emissions during the 4 measuring periods being in the interval of
40-110 ppmv which equals to 0.2-0.9% of N-removed (Table 4). The lowest N2O emissions (i.e.
0.2%) were obtained when the average DO level in the water phase was about 0.5 mgO2/L higher
than during the other periods and the NH4 level in the MBBR was lower than usual (<50 mgN/L).
Table 4. Average N2O emissions from the ANITA Mox process in Sjölunda.
Duration Data points
N-N2O prod.
Mean N2O level
Period (2011)
(h)
(No.)
(% N-removed)
(ppmv)
25-27/04
55
345
0.9
113
17-23/06
137
855
0.7
104
27-28/06
20
127
0.2
37
08-13/07
127
780
0.8
108
The N2O emissions from the ANITA Mox process (0.2-0.9% of N-removed) are in the low range of
what has been previously reported for different full-scale sidestream anammox processes.
Kampschreur et al. 2008 measured an overall N2O emission of 2.3% of N-removed in a 2-stage
nitritation (SHARON) / anammox (air-lift granular). However, Kampschreur et al. 2009 reported
lower N2O emission (1.7% of N-removed) in a 1-stage airlift granular reactor treating industrial
effluent. Joss et al. (2009) reported lower N2O emission in 1-stage granular SBR with continuous
aeration strategy (0.4% of N-removed) than with intermittent aeration (0.6% of N-removed).
Finally, Weissenbacher et al. (2010) measured N2O emission of 1.5% of N-removed in the
DEMON granular SBR in Strass, Austria. When comparing the ANITA Mox N2O emissions with
that from the sidestream nitrifying SBR treating the same reject water at Sjölunda WWTP (i.e. up to
4.1% of N-NH4 oxidized, Gustavsson et al. 2011), the GHG footprint is clearly in favor of the
ANITA Mox.
Performances of the ANITA Mox process at Sundet WWTP
The ANITA Mox process was started up at Sundet WWTP by seeding with 21m 3 of Anox K5
carriers from Sjölunda BioFarm (i.e. MBBR4) in December 2011. The seeding media represented
13% of total carrier in the reactor. Since the process was started up during the coldest winter
months, the temperature was kept around 28°C by batch wise heating of water when needed during
the first month of operation. To promote growth of anammox bacteria the reactor was fed with an
amount of reject water corresponding to an N-load slightly higher than the initial N-removal
capacity of the seeding media. The influent flow was continuously increased to promote the growth
of deammonification biofilm on the virgin media and the total amount of reject water was treated in
the ANITA Mox process after only 2 months of operation.
Results of the ANITA Mox plant operation since start-up are presented in Figure 6 and 7. Influent
NH4 level varied between 800-1100 mgN-NH4/L while effluent NH4 level was always below 200
mgN-NH4/L (most of the time <100 mgN-NH4/L) with an average NH4 removal of 88% (Figure 6a
and 7). Nitrate level in the MBBR outlet was below 100 mgN-NO3/L corresponding to a NO3-prod.
: NH4-rem. ratio in the range of 8-10% (Figure 6a and 6c). Since this value is lower than the
stoichiometric ratio of 11%, it is likely that some of the nitrate produced by anammox bacteria was
removed through heterotrophic denitrification. The reject water of Sundet WWTP contains very
little carbon source but the hydraulic retention time (HRT) in the reactor was longer than the design
value (i.e. 48h HRT compared to 24h expected initially) due a daily reject water flowrate of 150200 m3/d (Figure 6b) which was much lower than the 330 m3/d expected during the design phase.
The observed heterotrophic denitrification was probably due to some endogenous denitrification in
the system due to the very long HRT and the high T°C. Nitrite peaks over 10 mgN-NO2/L were
never observed even during start-up period and the average concentration was 2.6 mgN-NO2/L
(Figure 6a). These results are very similar to those from Sjölunda WWTP, confirming that nitrite
production is the limiting factor for the process. Since start-up, the applied N-load and N-removal
rate increased gradually to reach 0.55 kgN/m3.d and 0.5 kgN-NH4/m3.d respectively (Figure 6b).
The N-loading rate applied at Sundet WWTP was limited by the supply of reject water on site and
not by the process performance itself with only a maximum of 200 kgN/d available for the ANITA
Mox instead of 320 kgN/d initially expected by the site operator. N-loading and N-removal rate at
Sundet WWTP are expected to increase as soon as the amount of sludge and external organic waste
digested on site will increase and reach its design capacity.
200
1200
NH4-N in
NH4-N out
1100
NO2-N out
(a)
1000
NH4 in/out (mgN/L)
NO3-N out
180
160
900
140
800
120
700
100
600
500
80
400
60
300
NO3 out, NO2 out (mgN/L)
1300
40
200
20
100
0
0
NH4-N load
Reject Water Flow (m3/d)
0,5
(b)
500
0,4
400
0,3
300
0,2
200
0,1
100
0
%NH4rem, %TNrem, ratio NO3/NH4
600
0
0,9
38
0,8
36
0,7
34
0,6
32
0,5
30
0,4
TN removal %
NH4-N removal %
ratio NO3-prod/NH4-rem
T°C
0,3
0,2
T°C
NH4 load & NH4 removal rate (kgN/m3.d)
NH4-N rem
Reject water flow (m3/d)
0,6
28
(c)
0,1
26
24
22
0
20
0
30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540 570 600 630
Days
Figure 6. Operation results of Sundet ANITA Mox plant: NH4, NO3 and NO2 measured in inlet and
outlet (a); NH4 loading and removal rates and reject water daily flow in the MBBR (b); TN and NH4
removal efficiency, ratio NO3-prod. : NH4-rem. and T°C in the MBBR (c).
0,6
y = 0,88x
R² = 0,97
NH4 removed (kgNH4-N/m3.d)
0,5
0,4
0,3
0,2
0,1
0
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
NH4 load (kgNH4-N/m3.d)
3
Figure 7. NH4 load and removal rate (kgN/m .d) in Sundet WWTP ANITA Mox since start-up.
Energy Efficiency
Air blower supplying oxygen for the ANITA Mox reactor is also used to supply air to the plant grit
chamber making it very difficult to estimate the exact amount of air supplied to the ANITA Mox
reactor and its resulting energy consumption. A dedicated air flow meter measuring the exact
airflow sent to the MBBR tank was installed by the site operator mid-June 2013 making it possible
to estimate the specific energy consumption of the sidestream unit. With an average air flow of 245
Nm3/h since mid-June 2013, the energy consumption was estimated at 1.1 kWh/kgN-removed over
that period. This is lower than the energy requirement measured in the 50m3 MBBR at Sjölunda
WWTP (1.45-1.75 kWh/kgN-NH4 removed) confirming the high surface wall/volume ratio effect in
smaller unit. The use of fine bubble diffusers explained this relatively low energy requirement for
Sundet ANITA Mox plant together with the advanced aeration control strategy implemented.
Performances of the ANITA Mox process at Holbaek WWTP
At Holbæk WWTP an existing storage tank was available for reject water treatment. In addition,
treatment of leachate from a nearby landfill was required and this could be achieved by converting
the storage tank into an ANITA Mox. With given design load (120 kg N/d) and existing volume
(600 m3), there was no need using any carrier with very high protective surface area, why the
AnoxKaldnes K3 carrier (500 m2/m3) was chosen with a filling degree of 32%. Due to addition of
leachate water, temperature was expected to be lower and this was taken into consideration in the
design. The ANITA Mox process was started up in May 2012 by adding 20 m3 seeded K3 carrier
from the BioFarm at Sjölunda WWTP to 177m3 virgin K3 carrier, corresponding to 10% seeding.
During the first 10 weeks the nitrogen loading and removal increased steadily until a removal rate
of above 1 g N/m2, d (0.17 kg N/m2,d), Figure 8, was reached. At this stage reject water supply
started to be limited and also unstable due to issues with dewatering equipment. Shortly after this,
temperature in the reactor started to decrease and also failure of the on-line aeration equipment
occurred, leading to over-aeration with increased nitrate production up to as high as 120 mg NO3N/l. Getting aeration control back in operation again quickly optimised the aeration conditions and
decreased the nitrate produced to ammonia removed to values below the stoichiometric ratio (11%)
if nitrate were only produced by anammox bacteria, reaching values as low as 4-5%, indicating
reduction of nitrate by heterotrophic bacteria.
200
1000
180
900
(a)
800
700
NH4-N in (mg/l)
NH4-N out (mg/l)
NO3-N out (mg/l)
NO2-N out (mg/l)
600
500
400
NH4 load & removal (kgN/m³.d)
140
120
100
80
60
300
200
40
100
20
0
0
N-load (kgN/m3d)
N-removed (kgN/m3d)
T°C
35
0,2
30
0,15
25
0,1
20
(b)
0,05
0
% NH4 & N-rem, % NO3-prod/NH4-rem
160
T°C
NH4in and NH4out (mgN/L)
1100
NO2out and NO3out (mgN/L)
Due to winter conditions in Denmark, low temperature in combination with low loading and long
retention time dropped the temperature in the reactor well below 20°C for around 100 days of
operation, sometimes reaching as low as 15°C. In spite of this low temperature, ammonia removal
and nitrogen removal efficiency could be kept around 80% and 75%, respectively. During spring
and summer, temperature increased and the ANITA Mox continued to treat all available reject
water and additional leachate water to a high nitrogen removal efficiency (>90%).
15
10
90
80
70
60
50
% N-removal
40
% NH4-removal
30
% NO3-N prod/NH4-N rem
20
(c)
10
0
0
50
100
150
200
250
300
350
400
450
Days
Figure 8. Operation results of Holbaek ANITA Mox plant: NH4, NO3 and NO2 measured in inlet
and outlet (a); NH4 loading and removal rates and T°C (b); TN and NH4 removal efficiency, ratio
NO3-prod. : NH4-rem. (c).
Full-scale demonstration of IFAS ANITA Mox
The relatively high rate of N-removal in a MBBR biofilm comprised of aerobic/anammox bacteria
is explained by synergistic interaction between AnAOB and AOB bacteria in the biofilm. This
synergy is constrained by transport limitations and substrate availability inside the biofilm, which
depend on different environmental factors such as morphology, biofilm density and thickness,
temperature, substrate concentrations and shear stress. In order to improve the ANITA Mox MBBR
performance, substrate transport must be enhanced. Several studies investigated the effect of
combining suspended cultures and fixed biomass into one Integrated Fixed-Film Activate Sludge
(IFAS) for municipal (Al-Sharekh and Hamoda, 2001; Ødegaard et al., 2000) and industrial
(Wessman et al., 2004) wastewater treatment. Paul et al., (2006) have reported that a clear spatial
distribution of microbial population between floccular biomass (heterotrophs) and fixed biomass
(nitrifiers) leads to higher COD and N-removal performances.
Figure 9 depicts a conceptual model of MBBR and IFAS modes. The IFAS concept was applied to
ANITA Mox at lab scale (Zhao et al, 2013), yielding nitrogen removal rates 3-4 times higher than
the MBBR reactor operating in parallel on the same wastewater. The study also showed a
relationship between MLSS concentration and removal rate, as well as a distinct difference in
biological population composition between suspended and attached phases.
Figure 9. Conceptual model of distribution of bacterial populations involved in N-removal and
biofilm structure in pure MBBR versus IFAS ANITA Mox configurations (from Veuillet et al.
2013).
A full-scale IFAS demonstration system was started in the MBBR ANITA Mox plant at Sjölunda
WWTP. One of the four MBBR tanks filled at 50% with K5 carriers was converted to an IFAS
reactor by installing a conical clarifier for sludge retention (Feb 2013, Day 960). The clarifier had to
be fitted inside of the existing MBBR due to space constraint on site (Figure 10). The clarifier has a
surface area of 5.0 m2 and a total volume of 7m3.
Compared to typical operation for MBBR ANITA Mox, the IFAS reactor was operated at lower DO
(0.2-0.6mgO2/L versus 1.0-1.3mgO2/L) and at higher MLSS level (2-4g/L versus 0.02-0.2g/L).
Figure 10 - Retrofit of Existing MBBR ANITATMMox to IFAS Configuration
Preliminary results IFAS prototype. Figure 11 presents the results obtained before and after the
installation of the clarifier for operation as IFAS. The clarifier was installed on Day 960 and a stable
sludge separation performance was achieved after Day 985. During the stable period, average
ammonia removal efficiency was 95% and average TN removal efficiency was 85% while the ratio
NO3-N prod/NH4-N rem was around 10% (Figure 11c).
NH4in
NH4out
NO3out
NO2out
140
120
100
80
60
40
(a)
20
NO3 out, NO2 out (mgN/L)
NH4 in, NH4 out (mgN/L)
NH4 load & removal (kgN/m3.d)
%NH4 and %TN removal
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
0
NH4-load
3
NH4-removal
2,5
2
1,5
1
(b)
0,5
0
90
80
70
60
50
40
30
20
10
0
MBBR Transition
IFAS
%TN-removal
%NH4-removal
%NO3-prod : NH4-rem
(c)
930
950
970
990
1010
1030
1050
1070
1090
1110
1130
1150
Days
Figure 11. ANITA Mox performance before and after switching to IFAS configuration: NH4, NO3
and NO2 measured in inlet and outlet (a); NH4-N loading and removal rates (b); NH4-N and TN
removal efficiencies and % of NO3-N produced (c).
NH4-N loading and removal rates increased sharply after switching to IFAS mode reaching
2.2kgN/m3.d (Figure 11b) before dropping back to 1.2kgN/m3.d due to a shortage of reject water
and foaming in the reactor with the built-in clarifier, which led to difficulty controlling the MLSS
concentration. After modifying the operation, NH4-N loading and removal rates reached
2.2kgN/m3.d on Day 1030 and then gradually increased to reach around 3kgN/m3.d. Despite of the
MLSS variation in the IFAS tank mostly due to fluctuating influent TSS concentration (Figure 12),
nitritation in the suspended sludge was enhanced at bulk DO concentration between 0.2 to 0.5mg/L.
Compared to the pure MBBR operation, higher nitrite was observed (4 to 8mgNO2-N/L) with the
IFAS configuration. As indicated by the low ratio of NO3-N prod/ NH4-N rem measured in the
reactor (<10%), the low DO condition applied in the IFAS reactor was sufficient to repress the
NOB growth in the suspended sludge even with the higher nitrite level. Due to the improvements on
both nitritation and anammox activities with the IFAS mode and optimal microbial population
distribution between biofilm and suspended sludge, the NH4 removal rate increased by 200-300%
compared to the pure MBBR configuration.
MLSS (mg/L)
TSSin (mg/L)
SVI (mL/g)
180
160
140
120
100
80
SVI (mL/g)
TSSin & MLSS (mg/L)
200
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
60
40
20
930
950
970
990
1010
1030
1050
Days
1070
1090
1110
1130
0
1150
Figure 12. IFAS ANITA Mox suspended sludge concentration, SVI and TSS level in the incoming
reject water.
This IFAS full-scale prototype also provided very useful design parameters with regard to the
clarifier in term of SVI, sludge concentration factor, TSS level in treated effluent, and influence of
incoming TSS (Figure 12). The goal of the clarifier in the IFAS ANITA Mox process for sidestream
treatment is only to increase the MLSS in the MBBR tank and provide better nitritation
performances through advanced control of the SRT and bulk DO in the tank. The clarifier is not
used to retain anammox bacteria in the system. Sludge settling performance in the clarifier effluent
is not a critical parameter for the clarifier design, since this stream is sent back to the head of the
plant.
The choice between pure MBBR and IFAS configuration for sidestream treatment is site-specific
and depends on the existing tank volume available for reuse as a deammonification process. The
IFAS reactor is more compact than MBBR making it suitable when space is an important factor.
The need for a downstream clarifier and RAS pumping must be factored into the evaluation when
considering IFAS for sidestream treatment together with the TSS level fluctuation in the effluent to
be treated.
For mainstream deammonification, the IFAS solution has the advantage of being more readily
retrofitted in existing activated sludge systems. Mainstream IFAS ANITA Mox is currently being
tested at pilot scale at three WWTPs with different configurations and climates (i.e. after primary
settler + HRAS in Sweden, after UASB + HRAS in Middle East, after CEPT + HRAS in France).
IFAS ANITA Mox is also currently tested in several parallel 8L units at different COD/N ratio
(from 0.5 to 2) to investigate the maximum COD/N ratio that can be applied on IFAS ANITA Mox
and the impact on the overall performance and design.
CONCLUSIONS
•
•
With 4 full-scale systems in operation and others in progress, the ANITA Mox MBBR process
is a robust deammonification technology to address the issue of increasing N-load coming from
advanced sludge treatment processes while while aiding efforts towards energy efficiency.
After 4 months operation, the first full-scale ANITA Mox MBBR plant at Sjölunda WWTP
attained N-removal of 1.2 kgN-NH4/m3reactor.d with 90% NH4 removal efficiency with no need
of pre-treatment or chemicals.
•
•
•
•
•
•
The combination of carriers with very large protected surface area and carrier retention sieves
provides a robust and simple method to retain anammox biomass in the system independently of
the flow or TSS variations observed with sidestream reject water.
Energy consumption of the ANITA Mox MBBR process measured at Sjölunda WWTP
averaged around 1.5 kWh/kgNH4-N removed in a 50m3 MBBRs equipped with medium bubble
aeration. The energy consumption measured at the 300m3 ANITA Mox plant at Sundet WWTP
averaged 1.1 kWh/kgN-removed with fine bubble diffusers. This low energy consumption is
achieved in part with an advanced aeration control strategy, which optimizes the aeration
intensity in real-time.
The average N2O emissions from the ANITA Mox MBBR process (i.e. 0.2 – 0.9% of Nremoved) is in the low range of what has been previously reported for different full-scale
sidestream anammox processes.
Results from the new full-scale IFAS ANITA Mox operation demonstrate so far a 200-300%
improvement in N-removal rate compare to pure MBBR configuration with good sludge settling
properties.
In IFAS mode ANITA Mox, low DO (0.2 to 0.6 mg/L) and SRT control are capable of
repressing NOB in IFAS system and the easy physical separation between AOB-rich suspended
sludge and anammox-rich biofilm carriers through the use of non-clogging sieve is a clear
advantage to secure the retention of anammox in the system.
IFAS ANITA Mox opens new attractive solutions for Mainstream N-removal application due to
the potential for retrofit of IFAS process into activated sludge systems with existing clarifiers.
ACKNOWLEDGMENTS
The authors would like to acknowledge all the personnel at Sjölunda WWTP (Malmö, Sweden) and
Sundet WWTP (Växjö, Sweden) for their kind assistance with the ANITA Mox operation.
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