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 island’s 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 plant

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 Federation’s Award for Outstanding Achievement in Water Pollution Control for its significant contribution to improving water quality in New York Harbor.

The wastewater treatment process

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 treatment

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 called “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 City’s 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 River’s biosolids are either thermally dried into fertilizer pellets, composted, or alkalline stabilized into a product which resembles soil and is used as an agricultural liming agent.

Odor control

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 River’s 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.

More information

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