North River Wastewater Treatment Plant
The New York City Department of Environmental Protection’s (DEP) Bureau of Wastewater Treatment manages a comprehensive program to improve water quality in the New York City area. The City's 14 wastewater treatment plants, including the North River facility, play a crucial role in the City’s efforts to improve water quality. Also called sewage treatment or water pollution control plants, these facilities remove most pollutants from used water before it is discharged into local waterways. New York City's plants treat about 1.4 billion gallons of wastewater from homes, businesses, schools, and streets in the five boroughs every day.
Effective wastewater treatment is critical to the quality of life and the physical health of New York City residents and visitors. It not only protects people who use local beaches and waterways for swimming, fishing and other recreational activities, it also protects local wildlife and their habitats.
Improving the Hudson's Water Quality
The North River wastewater treatment plant is located on the Hudson
River, west of the West Side Highway from 137th Street to 145th Street.
The plant provides wastewater treatment for the hundreds of thousands
of people who live and work in or visit the west side of Manhattan,
from Bank Street in Greenwich Village to Inwood Hill at the islands
northern tip. North River treats about 125 million gallons of wastewater
every day during dry weather, and it is designed to handle up to 340
million gallons a day when the weather is wet.
North River's history
From the first proposal in 1914, seven locations were investigated
as possible sites for the construction of a plant to handle the sewage
flow from western Manhattan. However, it was not until 1962, after
considering several locations, that the City Planning Commission held
a public hearing and finally approved the present site for the treatment
plant. Design studies were started in the early 1960s and detailed
plans were finished in 1971. Construction of the foundation platform
was completed in 1978.
Construction of the treatment plant went forward in two phases. Work
on the advanced preliminary treatment facilities began in 1983; the
secondary treatment facilities were started in 1985. In March 1986,
advanced preliminary treatment went into operation, eliminating the
daily discharge of raw sewage into the Hudson River for the first time
in the City's history. Secondary treatment began in April 1991.
The North River wastewater treatment plant is built on a 28-acre reinforced
concrete platform over the Hudson River. It rests on 2,300 caissons
pinned into bedrock up to 230 feet beneath the river. The roof of the
building is the home of Riverbank State Park, a popular recreational
facility with three swimming pools, an amphitheater, an athletic center,
a skating rink, a restaurant and sports fields and, of
the two New York State park facilities in the City, the only one built
on top of a water pollution control plant.
North River has been widely recognized for its innovative design.
Its many awards include citations from the Concrete Industry Board,
the National Society of Professional Engineers, the New York State
Association of Architects, and the City Club of New York. In 1994,
the plant received the Water Environment Federations Award for
Outstanding Achievement in Water Pollution Control for its significant
contribution to improving water quality in New York Harbor.
Several stories underground, wastewater flows into the North River
plant from an 11-mile-long intercepting sewer that extends along Manhattan's
west side. Upon entering the plant, the wastewater first passes through
upright bars that remove large items, including rags, sticks, newspapers,
cans and other debris. The trash is automatically scraped from the
bars and later transported to a landfill. Five main sewage pumps lift
the wastewater to the surface level primary settling tanks. The flow
of the water is slowed, allowing the heavier solids to settle on the
bottom and the lighter materials to float. Oil and grease are skimmed
from the top of the tanks and the heavy solids, called primary
sludge, are scraped off the bottom for further processing.
The partially-treated wastewater then flows to the secondary treatment
system. Secondary treatment is called the activated sludge process,
because air and "seed" sludge from the plant treatment process
are added to the wastewater to break it down further. Air pumped into
five, 30-foot-deep aeration tanks stimulates the growth of oxygen-using
bacteria and other tiny organisms that consume most of the remaining
organic materials that pollute the water.
The aerated wastewater then flows to 16 final settling tanks, where
heavy particles and other solids again settle to the bottom. Some of
this sludge is recirculated back to the aeration tanks as "seed" to
stimulate the treatment process. The remaining solids are removed and
join the primary sludge for further processing in sludge-handling facilities.
To destroy disease-causing organisms, the wastewater is disinfected
with sodium hypochlorite, the same chemical found in common household
chlorine bleach. The treated wastewater, called effluent, is then released
into the Hudson River.
Sludge produced by primary and secondary treatment is approximately
97 percent water, and must be concentrated for further processing.
It is sent to thickening tanks for a period of up to 24 hours, where
it settles to the bottom. The water that remains is directed back to
the aeration tanks for additional treatment.
The thickened sludge, which is about 96 percent water, is then placed
in oxygen-free tanks called digesters and heated first to 95 degrees
fahrenheit. This stimulates the growth of anaerobic bacteria (bacteria
that thrive without oxygen), which consume the organic material in
the sludge. Methane gas, one of the byproducts of the digestion process,
is used as fuel in certain plant operations.
Converting sludge into biosolids
After digestion, the sludge is dewatered. Dewatering reduces the amount
of water the sludge contains, producing a moist, soil-like substance
biosolids that is easier to handle. Because North River
has no dewatering facilities, sludge from the plant is transferred
by boat for dewatering at the Wards Island wastewater treatment plant,
the site of one of the Citys eight dewatering facilities.
After dewatering, all of the City's biosolids, including those generated
at North River, are recycled and reused. The biosolids are removed
from the dewatering facilities by companies that have been awarded
long-term contracts by the City. These companies either convert biosolids
into environmentally safe fertilizer products or directly apply them
onto land to enrich nutrient depleted soil. North Rivers biosolids
are either thermally dried into fertilizer pellets, composted, or alkalline
stabilized into a product which resembles soil and is used as an agricultural
To improve the control of odors from the plant, New York City has
recently spent an additional $55 million beyond the cost of construction
of the original odor control facilities. North Rivers odor control
facilities are among the most elaborate in the country.
During the odor control process, plant air is pumped into a large
tank and scrubbed clean with a mixture of two chemicals, sodium hydrochloride
and sodium hydroxide (lye). The air is then funneled through activated
carbon filters, which absorb odors and chemicals and remove the remaining
odor-producing particles. The air is then released through 100-foot
ventilation stacks on the plant roof.
Monitoring the system
All of the plant's systems are controlled by a sophisticated computer
system. From the main control console, operators can oversee plant
operations, energy use and North River's security system.
For more information about the New York City water
supply or wastewater treatment systems,
contact us at:
New York City Department of Environmental Protection
Bureau of Public Affairs
59-17 Junction Boulevard, 19th floor
Corona, NY 1136