xvEPA
Wastewater Technology Fact Sheet
Side Stream Nutrient Removal
United States
Environmental Protection
Agency
INTRODUCTION
A significant nutrient load can be generated
internally by publicly owned treatment works
(POTWs). These nutrients can be found in the
reject water, also known as side streams, of
many municipal wastewater and sewage sludge
treatment processes. These side streams include
the reject stream from membranes, supernatant
liquid from sludge digesters, and the
centrate/filtrate return stream from sewage
sludge dewatering processes, among others.
Most of these side streams are conventionally
returned to the headworks of the POTW, where
they are combined with the normal influent.
Estimates of the nitrogen load from this side
stream return are between 15 and 30 percent of
the total nitrogen load on the process (Solley, D.
2000).
Recently, there has been research into the
separate treatment of these high-nutrient side
streams. It is reported to be more efficient and
cost effective than the conventional method of
returning these side streams untreated to the
headworks of the plant. The use of side stream
treatment is intended to decrease the loading on
the main nutrient removal process, resulting in
lower effluent nutrient concentrations (Vandaele
et al. 2000).
Several relatively new processes have been
developed to remove nitrogen in high-
concentration side streams from biosolids
processing—SHARON®, ANAMMOX®, and
InNitri® (Warakomski et al. 2006), and BABE®
(STOWA 2006). Each procedure has unique
characteristics that remove nitrogen more cost
effectively. SHARON® incorporates a different
metabolic pathway than is usually implemented
in wastewater treatment. InNitri® and BABE®
use bioaugmentation (the seeding of specific
strains of organisms to achieve desirable results)
in a new way, and ANAMMOX® uses an
entirely new group of bacteria to oxidize
ammonia anaerobically.
SHARON PROCESS
1. Description and working principle
The SHARON (Single reactor for High activity
Ammonia Removal Over Nitrite) process takes
place in a completely mixed reactor without
biomass retention. It has been developed to
treat high strength ammonia side streams from
sludge digestion. The conventional means of
converting ammonia to nitrogen gas is by
utilizing the nitrification/denitrification process.
In the SHARON® process, ammonia is
converted directly to nitrite (as opposed to
nitrate in conventional methods), and then
directly to nitrogen gas (Solley, D. 2000). The
conversion from ammonium to nitrite is
described by the following formula:
NH4+ + 1.5 O2 ^> NO2" + H2O + 2 H+
(STOWA 2006)
The ammonia oxidation is stopped at the nitrite
step by operating the SHARON® process at an
elevated temperature. At higher temperatures,
the ammonia oxidizers grow significantly faster
than the nitrite-oxidizing bacteria. In this
process the hydraulic retention time (HRT) is
equal to solids retention time (SRT). Therefore
the slow-growing nitrite oxidizers are washed
out of the system and the ammonia oxidization
is stopped at nitrite.
This is an exothermic process which operates at
process temperatures between 30 and 40 degrees
Celcius (°C) (86 to 104 degrees Fahrenheit (°F).
Depending on the ammonia concentrations in
the side stream being treated and final effluent
limitations, hydraulic retention times may be in
the range of 1 to 2 days (Solley, D. 2000).
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Temperatures of side stream water from
digesters can be expected to be generally around
25 to 30 °C. The exothermic microbiological
activity in the SHARON® reactor produces a
temperature rise of approximately 5 to 8 °C.
Depending on the local climate, additional
heating might be required only in wintertime.
2. Design guidelines/Technical data
Two wastewater treatment plants (WWTPs) in
the Netherlands utilizing the SHARON® process
have been studied to determine their
performance and costs. The SHARON® process
takes place in a single reactor, therefore, the
amount of land required can be much less than
expanding conventional nitrification/
denitrifi cation systems. The design
specifications for the SHARON® process at the
two Dutch WWTPs (Utrecht and Dokhaven) is
presented below.
Table 1.
Process design specifications
Parameter
Tank volume
Design flow
Maximum flow
Design N-load
Maximum N-load
Influent NH4 cone.
Aerobic retention time
Anoxic retention time
Units
m3
m3/h
m3/h
kg/d
kg/d
gN/l
d
d
WWTP
Utrecht
4.500
35
62.5
420
900
0.5-0.7
2.5
1.25
WWTP
Dokhaven
1.800
31.5
50
540
830
1-1.5
1
0.5-1.4
The Dokhaven WWTP operates in an
aerobic/anoxic cycle. The Utrecht WWTP
utilizes a two reactor continuous system (Solley,
D. 2006). For the Utrecht facility, the length of
one aerated period can be dependent on inlet
flow and pH set points. During aerobic periods,
the pH will decrease; during anoxic periods, the
pH will increase. This results in a discernible
pattern. The fluctuations in pH can be
addressed with process controls.
3. Performance
Performance at WWTP Dokhaven (Rotterdam,
The Netherlands).
The SHARON® process was first introduced at
the Dokhaven WWTP in 1997. As shown
below, the ammonium concentration in the
effluent from has continued to decrease
(STOWA 2006).
Table 2.
Average Ammonium effluent concentration
- Dokhaven WWTP
Year
1997-1998
1999
2000
Average NH4+ effluent.
9.6
6.2
5.2
cone, [mg/l]
Removal efficiencies of ammonia during this
time period have averaged in the 70 to 90
percent range, with the process becoming more
efficient in more recent years.
SHARON®/ANAMMOX® PROCESS
1. Description and working principle
The ANaerobic AMMonium Oxidation
(ANAMMOX®) process is a variation on the
SHARON® process described previously. In the
ANAMMOX® process, ammonium is converted
to dinitrogen gas (TSk). The combination of the
SHARON® process with the ANAMMOX®
provides an efficient and cost effective means to
treat nutrient rich side streams (STOWA 2006).
Treatment step 1: SHARON® process.
The SHARON® process is used to produce an
ammonium-nitrite mixture. For the SHARON®/
ANAMMOX® process however, the goal is to
convert only 50 percent of the ammonium to
nitrite so the difference in the SHARON®
portion of this process is the conversion of only
50 percent of the ammonium. To ensure that
only 50 percent of the ammonium is converted
to nitrite, the oxygen supply is limited.
Treatment step 2: ANAMMO^1 process.
In this treatment step, the ammonium-nitrite
mixture produced in the SHARON® reactor is
converted to nitrogen gas. Ammonium is used
as an electron donor under anoxic conditions.
The conversion of ammonium and nitrite to
nitrogen gas is described by the following
formula (STOWA 2006):
NO2" + NH4 => N2 + 2 H20
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The bacteria involved in the reaction are
autotrophic do not need the addition of an
external carbon source.
Since the ANAMMOX® bacteria have a slow
growth rate (doubling in 10 days at 30°C)
(STOWA 2006), sufficient volume must be
available to prevent wash out of the bacteria.
Sequential batch reactors have been used for
this purpose in pilot tests (STOWA 2006).
The treatment sequence of the combined
SHARON®/ANAMMOX® process is depicted
in Figure 1.
Sharon
(Chemostat)
Anammox
(SBR)
Figure 1. SHARON/ANAMMOX process
2. Design and Application
When sludge thickening and dewatering occur
before digestion, higher ammonia concentration
and lower overflow rates result.
WWTP Dokhaven (Rotterdam, The Netherlands):
In 2002, the Dokhaven WWTP's SHARON®
reactor was combined with an ANAMMOX®
system. The installation began operating in
June 2002 (STOWA 2006).
3. Performance
It is estimated that the combined SHARON®/
ANAMMOX® process can achieve an overall
nitrogen removal rate of 90 to 95 percent. Since
the process does not need an external organic
source and operates under low oxygen
concentrations, cost savings can be realized over
the traditional nitrification/denitrification
systems (Solley, D. 2000).
INNITRI® SYSTEM
1. Description and working principle
InNitri® (Inexpensive Nitrification) is a new,
side stream nitrification process offered by
Mixing & Mass Transfer (M2T) Technologies,
Inc. It allows nitrification at short SRT values,
even at low winter temperatures and provides
nitrification in a substantially smaller aeration
tank than is required for conventional
nitrification design. The InNitri® process was
developed to provide an inexpensive alternative
for plants in northern climates that need to
upgrade their air or pure oxygen activated
sludge process for year-round nitrification or
nitrogen removal (M2T 2002).
In general, the InNitri® process consists of
supplemental nitrifiers being added constantly
to the main activated sludge process to replenish
nitrifiers removed with the wasted activated
sludge. The supplemental nitrifiers are grown in
a separate, small, side-stream aeration tank
using either ammonia available in the digested
sludge dewatering liquid and in the digester
supernatant or commercial ammonia.
A conventional secondary treatment plant might
consist of primary sedimentation, an aeration
tank, secondary clarification, and sludge
thickening, followed by anaerobic digestion and
sludge dewatering. Upgrading such a plant to
provide year-round nitrification using the
InNitri® (short Solids Retention Time (SRT)
nitrification) process requires the addition of a
small aeration tank and clarifier for growing
nitrifiers. In the process, the warm (typically 30
to 35 °C) dewatering liquid containing a high
ammonia content (between 300 and 900 mg/L)
is mixed with a small portion of primary
effluent (to adjust the temperature and provide
organic matter), and it is nitrified in the side
stream nitrification aeration tank. A portion of
the resulting biological sludge—containing a
high percentage of nitrifiers—is discharged into
the main aeration tank and provides the main
activated sludge process with supplemental
nitrifiers. This results in the plant being able to
provide year-round nitrification.
The same process can also be applied in plants
without digesters. In this case, commercial
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ammonia is used instead of the dewatering
return stream.
The treatment sequence of the InNitri® system is
schematically depicted in Figure2.
Figure 2. InNitri® system
2. Design Guidelines/Technical Data
The conventional nitrification process typically
consists of a complete mix-steady-state aeration
tank with 6 hr. hydraulic detention time,
operating at 10 °C, and receiving an influent
containing 25 mg/L of TKN (with 25 percent of
the TKN contained in the side-stream
dewatering liquid). To demonstrate the
difference between the conventional nitrification
process and nitrification with supplemental
nitrifiers (InNitri process), KOS (1998)
presented theoretical equations and results of
modeling for a typical WWTP. Mathematical
modeling results showed that, for conventional
nitrification at 10 °C, as the operating SRT is
decreased, the concentration of nitrifiers also
decreased, while ammonia nitrogen in the
effluent increased. For the InNitri® approach,
results indicate that nitrifiers are present in the
main aeration tank at all SRT values.
Nitrifiers cannot be washed out from the
aeration tank even if operated at lower SRT
values; therefore, partial nitrification takes place
even at extremely low SRT values. In other
words, the InNitri® process does not have a
minimum SRT under which nitrification would
not occur. Therefore, it will be much more
stable and may not require as high a safety
factor as conventional nitrification. The
modeling was repeated at temperatures from 7.5
to 20 °C. Results showed the InNitri® process
allowed for significantly lower design SRT than
the conventional nitrification to achieve the
same effluent ammonia concentration. Where
the design effluent ammonia concentration is
2.0 mg/1, the minimum required design SRT for
the InNitri® process is about 60 percent of that
required for conventional nitrification. A
comparison of the SRT necessary for
nitrification using InNitri® versus conventional
nitrification showed significant reductions in
costs for low temperature wastewaters using the
InNitri® process.
Research by the University of Manitoba
indicated that the transport of nitrifying sludge
from a warm side stream reactor to a cold
mainstream reactor should pose no process
problems. Also, the evaluation of the process to
upgrade an existing facility showed significant
cost savings using the InNitri® system versus
using conventional and other advanced
nitrification processes.
Brinjac, Kambic, and Associates (2000)
completed a feasibility analysis for upgrading
the Harrisburg City Advanced Wastewater
Treatment Facility (Harrisburg, Pennsylvania)
for nutrient control. This facility was considered
to be typical of many of the plants designed to
meet the effluent requirements of the federal
Clean Water Act. The facility is in the colder
climate in northeastern United States and is a
principal point source contributor of nitrogen to
the Susquehanna River. The river flows to the
Chesapeake Bay where efforts are underway to
improve water quality by reducing the nutrient
load to the bay. The facility is site-constrained
with little room for flow or process expansion.
Due to the results of the feasibility study,
Brinjac, et al. recommended that the facility
implement the InNitri® process. (As of this date,
the city has not yet initiated the project.)
3. Performance
Currently, there are no full-scale InNitri®
installations. Capital and operations and
maintenance (O&M) costs for the system vary
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by the type and size of facility. For site-specific
unit design and costs, contacting the
manufacturer directly is recommended.
BABE PROCESS
1. Description and working principle
The BioAugmentation Batch Enhanced
(BABE®) process is comprised of a single batch
reactor. Side stream waters high in ammonia
content and return activated sludge (RAS) from
the main biological treatment process are
combined (STOWA 2006) with previously
settled sludge in the batch reactor. The RAS is
used to augment the bacteria in the settled
sludge. By utilizing a batch reactor, the long
residence times necessary to grow both the
nitrifying and denitrifying bacteria are possible.
There are five phases to the BABE® process: 1)
filling, 2) mixing and aeration, 3) mixing, 4)
settling, and 5) settling and decant (STOWA
2006).
The first two steps are done under aerobic
conditions. The third involves mixing without
aeration to achieve anoxic conditions. This
condition is conducive to denitrification. Steps
four and five complete the process.
2. Design and Performance
As with the SHARON® process, testing has
shown that higher concentrations of ammonia in
the influent to the BABE® process are
preferable (STOWA 2006). The BABE®
process operates at temperatures between 20 and
25 degrees C, which is lower than the
SHARON® process.
If the process temperature in the BABE® reactor
is less than 20°C, the reactor volume must
increase dramatically. However, temperatures
greater than the normal operating temperature
range have minimal impact on the process.
OPERATION AND MAINTENANCE ISSUES
The SHARON® process has been shown to be
able to tolerate suspended solids in the influent
to the process. However, pH control is vital to
the proper operation of the process and robust
process controls must be in place to respond
quickly to changes in process temperatures and
pH.
The ANAMMOX® process can respond well to
biomass that is washed out of the SHARON®
process in a combined system. Due to the slow
growth of the denitrifying bacteria, long start-up
times are required. Again, pH and temperature
control are imperative for proper operation of
the system.
The InNitri® System's advantages are a low
capital cost and small footprint at a facility. It
also appears that process control is not as vital
(M2T 2002) when compared to other side stream
nitrification processes.
COSTS
The SHARON® process has been compared
with other techniques for nitrogen removal from
reject water and was found to be the least
expensive under Dutch circumstances. A cost
estimate of 1.5 Euro/kg Nremoved (approximately
$2/kg Nremoved) was given.
The investment costs for a SHARON®/
ANAMMOX® installation with a capacity of
1.200 kg NH/t-N/day are estimated at 2 million
Euros (approximately 2.75 million U.S. dollars).
The operating costs are linked to the costs for
energy, methanol, and caustic chemicals
(STOWA 2006).
Actual costs for the InNitri® and BABE®
processes are not available; there is no full scale
implementation of these systems.
OTHER TECHNOLOGIES INCLUDE:
Plug-flow, activated-sludge with
denitrification filters
The Central Johnston County Wastewater
Treatment Plant in Smithfield, North Carolina
achieves biological phosphorus removal and
nitrogen removal in a plug-flow, activated-
sludge process and separate-stage denitrification
filters.
The plug-flow, activated-sludge process utilizes
anoxic and aerobic basins in series. This was a
retrofit design implemented by facility
personnel.
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The two-stage biological processes in series
offer high efficiency in nutrient removal at
minimal costs. The source of wastewater is
typical residential customers in the suburb of a
large, metropolitan area. The BOD to total
phosphorus (TP) ratio averages 55:1. The
retrofitted, activated-sludge process consists of
an anoxic stage with a 4.8-hour residence time,
followed by an aerobic stage in two tanks with a
residence time of 11.5 hours. The operating
strategy developed at this facility is unique
because the sludge blanket at the clarifiers is 3-
4 feet deep, and the return activated sludge
(RAS) flow rate is maintained at a low (10-25
percent) portion of the plant flow. The second-
stage denitrification filters then remove the
remaining nitrogen with a methanol feed.
The design and operation result in a high level
of removals with an effluent TN concentration
of 2.14 mg/L and an effluent TP concentration
of0.26mg/L.
COSTS
The costs of removal were very low for both
capital and O&M. The life-cycle cost for TP
removal was $2.21/lb of TP removed, while the
life-cycle cost for TN removal was $0.98/lb of
TN removed, including the cost for methanol.
The capital cost for the flow capacity was
$0.58/gallon per day (gpd) capacity.
A/O Process with Alum Feed
The Clark County Water Reclamation Facility
(WRF) is in Las Vegas, Nevada. Three major
factors contribute to reliable phosphorus
removal and nitrification at this facility: (1)
multiple chemical feeding, (2) good biological
phosphorus removal with in-plant volatile fatty
acid (VFA) generation and full nitrification, and
(3) good tertiary filters for suspended solids
removal. This combination of chemical,
biological, and physical processes in series is
effective in providing exceptionally low
phosphorus (0.09 mg/L) and ammonia-nitrogen
(0.05 mg/L) concentrations.
COSTS
The capital cost for phosphorus removal and
complete nitrification is estimated to be
$2.01/gpd. The unit costs for capital and O&M
were $5.43/lb for phosphorus and $1.38/lb of
nitrogen removed. The unit costs for O&M were
$1.84/lb of phosphorus removed and $0.51/lb of
nitrogen removed.
The Clark County plant operation has been
successful in reducing effluent phosphorus to a
level that is considered to be the state-of-the
science at the existing plant using a combination
of biological and chemical treatment processes
in series with good reliability. The plant is
almost at capacity and yet has produced effluent
far below the discharge limits. The technique of
using several different technologies in series can
achieve the treatment objective especially when
the operation is computer controlled and the
system has been designed with a reasonable
amount of redundancies to allow for repairs and
routine maintenance. Operational costs are
reasonable, with life-cycle costs of $5.24/lb and
$0.98/lb for phosphorus and nitrogen removal,
respectively.
In addition to the technologies mentioned
above, there are other treatment options
available. For their applicability in removing
nutrients at wastewater treatment facilities,
examine::
1. Bioaugmentation with recycle treatment
- MAUREEN (Mainstream Autotrophic
Recycle Enabling Enhanced N-removal)
2. Fixed-film nitrification and
de-ammonification processes
- OLAND (Oxygen Limited Aerobic
Nitrification-Denitrification)
- CANON (Completely Autotrophic Nitrogen
Removal Over Nitrite) (Stensel 2006)
SUMMARY
1. The treating of recycle side streams can
provide more stable and effective
nitrification.
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2. Recycle side stream treatment can increase
nitrification capacity of existing systems
(BABE®, InNitri®, and MAUREEN).
3. Recycle side stream treatment can help
reduce carbon demand for nitrogen removal
T®
(SHARON*, ANAMMOX®,
CANON) (Stensel 2006).
OLAND, and
Impe. 2000. Ammonia removal from
centrate of anaerobically digested sludge:
State of the art biological methods.
1st World Water Congress of the IWA
4(280-287).
ACKNOWLEDGMENTS
The authors of this report are grateful for the
information provided by the Central Johnston
County Wastewater Treatment Plant-Smithfield,
North Carolina and the Clark County Water
Reclamation Facility - Clark County, Nevada.
REFERENCES
M2T (Mixing & Mass Transfer Technologies,
Inc.) 2002. The InNitri® Nitrification
System: An Innovative Wastewater
Treatment Process.
Solley, D. 2000. Upgrading of Large
Wastewater Treatment Plant for Nutrient
Removal. Churchill Fellowship 2000
Report. The Winston Churchill Memorial
Trust of Australia.
Stensel, H.D. 2006. Sidestream Treatment for
Nitrogen Removal.
STOWA (Dutch Foundation for Applied Water
Research). 2006. SHARON and
SHARON/ANAMOXProcess Sheets.
Warakomski, A., R. van Kempen, and P. Kos.
2006. Microbiology/Biochemistry of the
Nitrogen Cycle Innovative Process
Applications. International Water
Association Proceedings, Moncton, New
Brunswick, Canada.
Vandaele, S., F. Bollen, C. Thoeye, E.
November, H. Verachtert, and J.F. van
vvEPA
United States
Environmental Protection
Agency
EPA 832-F-07-017
Office of Water
September 2007
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