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New York City was one of the first metropolitan areas in the United States to design, construct and operate a modern sewage treatment facility. In 1906 the Metropolitan Sewerage Commission of New York was created to study regional water quality conditions and formulated a plan for protecting and improving the state of New York Harbor. Although clear State or federal mandates for sewage treatment and water quality standards did not exist at the time, the Metropolitan Sewerage Commission envisioned the construction of up to 35 small sewage treatment facilities. Today, all five boroughs of New York City are served by 14 large water pollution control plants, operated and maintained by DEP.

Construction of the first modern sewage treatment facility was completed at Coney Island in 1935. By the 1970s, New York City had 12 plants in operation using a City-developed process called modified aeration, which removed 60%26#37; of conventional pollutants - far better than the 35%26#37; removal rates typically achieved elsewhere in the nation. However, the federal Clean Water Act of 1972 mandated specific standards for treatment plants and required 85%26#37; removal of conventional pollutants for all plant discharges.

As a result of this mandate, New York City redesigned or reconstructed its 12 existing plants, in addition to adding new ones in Manhattan and Brooklyn. Despite a national energy crisis and the City's fiscal difficulties in the mid-1970s, reconstruction of nine plants to full secondary treatment was completed by 1980 at a cost of $670 million. Initial construction of the thirteenth and fourteenth plants (North River and Red Hook) was completed in 1986 and 1988 at a cost of $1.5 billion. Upgrading treatment at two of the three remaining modified aeration plants was completed in 1995. Upgrading the final plant, Newtown Creek, is currently ongoing.

DEP manages a comprehensive program to improve water quality in the New York City area. Effective wastewater treatment is critical to the quality of life and the physical health of New York City residents and visitors. It protects local beaches and waterways for swimming, fishing and other recreational activities, as well protecting local wildlife and their habitats.

The Wastewater Treatment Process
Upon entering the plant, wastewater first passes through upright bars that remove large items, including rags, sticks, newspapers, cans and other similar material. 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 to the top. The 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 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 final settling tanks, where heavy particles and other solids settle to the bottom. Some of this sludge is re-circulated 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 the 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 New york Harbor.

Sludge Treatment
Sludge produced by primary and secondary treatment is approximately 97%26#37; water and must be concentrated for further processing. It is sent to thickening tanks for a period of up to 24 hours. The water that remains is directed back to the aeration tanks for additional treatment. The thickened sludge, which is about 96%26#37; 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 a 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 some plants have no dewatering facilities, sludge is transferred by boat for dewatering at one of the City's eight dewatering facilities. After dewatering, most of the City's biosolids, are used - either in a dewatered state or as thermally dried pellets - as fertilizers or soil enhancers in various locales around the country. A small portion of the biosolids is sent to a landfill outside the City.

Odor Control
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, which absorbs odors and chemicals and removes the remaining odor-producing particles, The air is released through ventilation stacks an the plant roof.