United States
Environmental
Agency
Selection
Office of Water
(4504F)
EPA842-F-95-001A
September 1995
&EPA
Biological Nutrient
Removal Project
Demonstrating Practical Tools For Watershed
Management Through The National Estuary Program
Long Island Sound, Connecticut And New York
Characteristics:
• Long Island Sound encompasses 1,300 square miles, with a drainage
basin of 16.000 square miles.
• Approximately 15 million people live within 50 miles of the Sound.
• The Sound's circulation patterns and bottom topography together create
a complex system, obscuring the impact of discharges.
The Problem:
Excessive levels of nitrogen from point and
nonpoint sources have contributed to a decrease in
the amount of available oxygen in the Sound.
• Low oxygen concentrations have led to
reduced growth, physiological stress of aquatic-
life, and migration offish to other areas.
• Of the 90,800 tons of nitrogen entering the
Sound per year, 32,400 tons come from point
sources, such as municipal sewage treatment
plants.
• Upgrading existing sewage treatment plants to
be able to remove nitrogen can be very costly.
The Project:
The project selected two treatment plants to test the
nitrogen reduction capability and cost savings of an
innovative technology called Biological Nutrient
Removal (BNR).
The National Estuary Program
JtLstuaries and other coastal and marine waters are national
resources that are increasingly threatened by pollution, habitat
loss, coastal development, and resource conflicts. Congress
established the National Estuary Program (NEP) in 1987 to
provide a greater focus for coastal protection and to demon-
strate practical, innovative approaches for protecting estuaries
and their living resources.
As part of this demonstration role, the NEP offers funding
for member estuaries to design and implement Action Plan
Demonstration Projects that demonstrate innovative approaches
to address priority problem areas, show improvements that can
be achieved on a small scale, and help determine the time and
resources needed to apply similar approaches basinwide.
The NEP is managed by the U.S. Environmental Protection
Agency (EPA). It currently includes 28 estuaries: Albemarle-
Pamlico Sounds, NC; Barataria-Terrebonne Estuarine Complex,
LA; Barnegat Bay, NJ; Buzzards Bay, MA; Casco Bay, ME;
Charlotte Harbor, FL; Columbia River, OR and WA; Corpus
Christi Bay, TX; Delaware Estuary, DE, NJ, and PA; Delaware
Inland Bays, DE; Galveston Bay, TX; Indian River Lagoon, FL;
Long Island Sound, CT and NY; Maryland Coastal Bays, MD;
Massachusetts Bays, MA; Mobile Bay, AL; Morro Bay, CA;
Narragansett Bay, RI;New Hampshire Estuaries, NH; New York-
New Jersey Harbor, NYandNJ; Peconic Bay, NY; Puget Sound,
WA; San Francisco Bay-Delta Estuary, CA; San Juan Bay, PR;
Santa Monica Bay, CA; Sarasota Bay, FL; Tampa Bay, FL; and
Tillamook Bay, OR.
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Introduction To Long Island Sound
Long Island Sound is bordered by Connecticut and portions
of New York City and Westchester, Nassau, and Suffolk
Counties in New York State. The resources of the Sound are
rich and diverse, benefiting local citizens, visitors, and wildlife.
With an average depth of 63 feet, the Sound is a major feeding
and spawning ground for numerous species of shellfish and
finfish, such as lobster, crab, clam, oyster, bluefish, striped bass,
herring, and flounder. The Sound also provides resting and
feeding grounds for herons, egrets, and migrating harbor seals.
The Sound's natural resources also support many recre-
ational activities, such as swimming, boating, and fishing. With
over 200,000 registered boats, over 700,000 recreational
fishermen, and 95 public beaches, the Sound's resources
provide $5.5 billion to the local economy each year.
Although still considered a relatively healthy waterbody, the
Sound and its marine resources are facing a crisis. In 1987.
many fishermen began noticing fish and lobster kills in the
Sound. Monitoring of the water column initiated by the Long
Island Sound Study indicated a high amount of nitrogen and low
dissolved oxygen levels. At one point, 40 percent of the Sound's
bottom waters had unhealthy levels of oxygen. Low levels of
dissolved oxygen threaten the variety and vitality of the Sound's
marine life. The main cause of this condition is excessive
nitrogen, a nutrient that enters the Sound through point and
nonpoint sources. Excess nitrogen fuels the growth of plank-
tonic algae. When the algae die, they settle to the bottom and
decay, using up oxygen in the process. The lack of available
oxygen in waterbodies is called hypoxia.
Studies indicate that the 45 sewage treatment plants dis-
charging directly into the Sound contribute 48 percent of the
nitrogen load. Historically, these treatment plants used pro-
cesses that remove only 10 to 20 percent of the total nitrogen
content from their waste stream, leaving high concentrations of
nitrogen in their effluent. It was clear from the results of the
studies that the nutrient removal capabilities of the wastewater
treatment plants must be improved.
New Technologies Needed
L onventional methods for nutrient removal were investi-
gated in an effort to reduce nitrogen inputs into the Sound. It
was soon discovered, however, that the cost of modifying all 45
treatment plants using conventional methods would cost up to $8
billion. Therefore, it became necessary to search for new, cost
effective techniques for removing nitrogen from the waste
stream.
The wastewater treatment facility in Stamford, Connecticut
had experimented with a process known as Biological Nutrient
Removal (BNR) since 1988. BNR is a form of sewage treatment
that uses biological organisms to remove nitrogen through two
reactions: nitrification and denitrification. Nitrification changes
ammonia into nitrates and nitrites, which can then be converted
into nitrogen gas through denitrification. Nitrogen is then
released into the air. Although BNR is temperature and oxygen
dependent, these factors can be controlled in most existing
Oxygen used up by
microorganism respiration
Oxygen trapped above
pycnocline
I
Oxygen ^1
Decomposition
Oxygen M
HYPOXIA
NUTRIENTS
Released by bottom sediments
SHELLFISH '
Unable to move from Hypoxia
\
SOURCE
FOR NEW
OXYGEN
PYCNOCLINE
ADVECTED
OXYGEN
The dynamics of hypoxia in Long Island Sound
treatment plants. Results from the Stamford facility suggested
that it was possible to achieve high rates of removal of total
nitrogen and phosphorous using BNR technology.
In addition to its potential for high nutrient removal rates,
BNR could be employed with only relatively minor changes in
operation at a nominal cost. A decision was made to further test
BNR technology at two sewage treatment plants that discharge
into the Sound: the facility in Stamford, CT and the Tallman
Island wastewater treatment facility located in New York City.
Overview Of Demonstration Facilities
L he Stamford and Tallman Island sites were chosen
because of their facility designs, past records of compliance with
permit limits, plant operator skills and controls, and the fact that
neither plant was at or over capacity. In addition, these plants
each used oxygen-supply systems typical of those in place at
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Wastewater
Influent
Screens
NO3~-N and
cultivated bacteria
Secondary
Settling Tank
>y
Disinfection
Denitrification
(Anaerobic or
Anoxic)
Nitrification
(Aerobic)
Example of biological nutrient removal process in an altered aeration tank.
other Long Island Sound treatment facilities, making project
results likely to be more broadly applicable.
The City of Stamford water pollution control facility is a 20
million gallon per day (MGD) secondary activated sludge
treatment plant, using mechanical aerators to supply air during
treatment. Stamford has been operational since 1976. Approxi-
mately 85 percent of the facility's influent is from domestic and
commercial sources, and 15 percent is from industrial sources.
An 80 MGD facility originally designed in the 1930s, the
Tallman Island water pollution control plant is located in College
Point, New York. The Tallman Island plant serves an urban
drainage area of approximately 26 square miles located just
south of New York City. Like the Stamford facility, it too is an
activated sludge treatment plant, but Tallman Island uses a
diffused air system. The wastewater system that feeds the
facility contains storm sewers, sanitary sewers, and combined
sewers.
Project Objectives
I here were four main objectives in implementing the
project:
Determine how much nitrogen could be removed by utiliz-
ing different process control techniques and expending
minimal capital costs.
Establish criteria for nitrogen removal procedures that
could be used by consulting engineers and plant managers
at other plants.
Study the effects of cold temperatures on biological
processes.
Establish a local source of expertise in BNR processes in
order to expand its use to other nearby sewage treatment
plants, if the methods proved to be suitable.
Implementing The Project
I n 1990, EPA awarded funding under the National Estuary
Program to the Stamford facility to continue its study of BNR
and to help the Tallman Island water pollution control facility to
initiate a nitrogen removal demonstration project. Some
modifications were necessary to enable the two facilities to
perform both nitrification and denitrification. At Stamford,
adjustments to the aeration system were made, and the Tallman
facility required installation of flow meters, samplers, baffles,
and mixers. None of these modifications required substantial
capital investment.
Once the facilities were equipped for BNR, variations of the
BNR system were tested for optimum nitrogen removal. For
both treatment plants, this was done by manipulating the
operating processes. The Tallman facility manipulated its
operating process in a five-phase chronological approach, in
which information from previous phases of the testing was
applied to the next phase. Stamford, already using nitrification,
tested three processes to determine the denitrification process
with the highest removal rate.
Both Stamford and Tallman evaluated BNR processes from
1990 to 1992. Specifically, wastewater was tested both before
and after treatment for various parameters such as nutrient
levels, temperature, oxygen, and pH. These tests were con-
ducted at least twice weekly so that any process changes needed
to keep nitrogen removal levels as high as possible could be
implemented. Laboratory studies were used to determine design
criteria for use by engineers and were performed at the begin-
ning of each month.
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Biological Nutrient Removal
Success Story
L he demonstration project was successful in meeting all of
its objectives. Both the Stamford and Tallman facilities
demonstrated a significant amount of nitrogen removal, with
rates of up to 83 and 73 percent, respectively. Because the
designs were somewhat experimental in nature, the plant
operators are confident that the initial nitrogen reduction rates
will increase as soon as the systems are optimized.
In addition, the BNR processes were instituted without
additional staff, extensive training, or costly modifications.
Because some of the operational tests used in the project are al-
ready performed at most secondary treatment plants, additional
training and equipment may not be needed at other plants that
implement BNR.
Overall, the success of this project has led to the planning of
wide-scale BNR implementation throughout the Sound. The
demonstration project has illustrated that BNR can be used
effectively at sewage treatment plants to reduce nitrogen levels
in discharge, without costly modifications. Regional expertise
has also been established and will help with continuing efforts
in Long Island Sound.
Lessons Learned
L he results of the BNR project showed that, with little or
no capital investment and only minor changes to existing
processes, secondary treatment plants can reduce the amount of
nitrogen discharged into Long Island Sound. Among the other
lessons learned:
Printed on recycled paper
• Although BNR was successful in reducing nitrogen in
treatment plant effluent, employing BNR in regions with
climates colder than those in the demonstration project
may not be effective since BNR processes are cold-
weather limited.
• The BNR process can occur with short detention times.
Consequently, most treatment plants, even those that have
reached or are over capacity, can utilize these techniques.
• The positive effects of the BNR demonstration project on
marine life in the Sound cannot be verified with just two
participating treatment plants. Because the Sound is so
vast, monitoring of conditions after widespread implemen-
tation of BNR will be necessary to see long-term effects.
The Long Island Sound Biological Nutrient Removal Project
serves as a model for other secondary treatment plants that
discharge into Long Island Sound. Facilities with similar
locations, climates, and operational elements may be able to
modify operations to reduce nitrogen in discharges.
For more information contact:
Mel Cote
U.S. EPA Region 1
JFK Building
Boston, MA 02203
Mark Tedesco, Technical Director
Long Island Sound Office
Stamford Government Center
888 Washington Boulevard
Stamford, CT 06904-2152
(617)565-4432
(617) 565-4940 FAX
(203)977-1541
(203) 977-1546 FAX
&EPA
United States
Environmental Protection
Agency
(4504F)
Washington, DC 20460
Official Business
Penalty for Private Use
$300
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