April 2007, Vol. 19, No.4

Plant Profile

North River Water Pollution Control Plant

PlantProfileMapApr07.jpg Location: New York City
Startup date: March 1986
Service population: 500,000 permanent residents, larger commuter population
Number of employees: 128
Design flow: 170 mgd (643,000 m3/d)
Average flow: 125 mgd (473,000 m3/d)
Peak flow: 340 mgd (1.3 million m3/d)
Annual operating cost: $8.5 million
 

New York City’s North River Wastewater Treatment Plant is built on a 28-ac (11-ha) reinforced concrete platform over the Hudson River. It rests on 2300 caissons pinned into bedrock up to 230 ft (70 m) 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. Upwards of 10,000 people visit the park on any given day.

New York City’s North River Wastewater Treatment Plant is built on a 28-ac (11-ha) reinforced concrete platform over the Hudson River. It rests on 2300 caissons pinned into bedrock up to 230 ft (70 m) 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. Upwards of 10,000 people visit the park on any given day.

North River has been widely recognized for its innovative design. Its many awards include citations from the Concrete Industry Board (New York), National Society of Professional Engineers (Alexandria, Va.), New York State Association of Architects (Albany), and City Club of New York. In 1994, the plant received the Award for Outstanding Achievement in Water Pollution Control from the Water Environment Federation (Alexandria, Va.) for its significant contribution to improving water quality in New York Harbor.

The plant began advanced preliminary treatment in March 1986. Until that time, untreated wastewater flowed into the Hudson River. However, planning for the plant began in 1962.

After considering several locations, the New York City Planning Commission finally approved the site, and design studies began in the early 1960s. 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. Secondary treatment began in April 1991.

The 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 mgd (473,000 m3/d) during dry weather, and it is designed to handle up to 340 mgd (1.3 million m3/d) during wet weather.

Liquid Processes
Several stories underground, wastewater flows into the North River plant from an 11-mi-long (18-km-long) intercepting sewer that extends along Manhattan’s west side. The wastewater first passes through six vertical traveling-rake bar screens before five 1740-hp (1300-kW) dual-fuel-engine main sewage pumps lift the wastewater to the eight surface-level primary settling tanks. Next, the flow enters five 30-ft-deep (9-m-deep) aeration tanks for activated sludge treatment. The aerated wastewater then flows to 16 clarifiers for final settling. Finally, sodium hypochlorite disinfects the effluent in four one-pass contact tanks before it flows into the Hudson River.

Solids Processes
Ten gravity thickeners concentrate primary and waste activated sludge for a period up to 24 hours. The thickened sludge, which is about 96% water, is then digested in eight anaerobic digesters at 95°F (35°C). The plant captures and uses the methane gas generated as fuel in certain plant operations.

After digestion, the liquid sludge is transferred by boat for dewatering at the Wards Island Wastewater Treatment Plant, the site of one of New York’s eight dewatering facilities.

All of the city’s biosolids, including those generated at North River, are recycled. North River’s biosolids are either thermally dried into fertilizer pellets, composted, or alkaline-stabilized into a product which resembles soil and is used as an agricultural liming agent.

Odor Control
Unlike most wastewater treatment plants, North River was built in the middle of a densely populated urban area. Problems such as odors were initially a huge issue, especially during startup. The covering of many process areas and the installation of vast amounts of odor-control equipment to serve these areas has greatly reduced the plant’s effect on its neighbors.

To improve the control of odors from the plant, New York City 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 then is funneled through activated carbon filters, which absorb odors and chemicals and remove the remaining odor-producing particles. The air then is released through 100-ft (30-m) ventilation stacks on the plant roof.

To keep the massive plant operating smoothly, more than 14,000 input–output points are monitored or controlled by a redundant network of distributed control units. Almost every plant function — such as various pressures, flows, temperatures, sequencing, dosing, and alarming — is capable of being monitored, controlled, or both. Automation provides ready display and reporting capabilities