Turning sewage into renewable energy

NYC wastewater-to-energy turns sewage treatment byproducts into renewable power, capturing methane biogas from sludge via anaerobic digestion, producing fuels like butanol from algae, and adding solar and wind to cut emissions and operating costs.

New York City’s sewage presents a daunting and costly challenge: it creates foul odors and often contaminates waterways.

But the city is now casting its sewage treatment plants and the vast amounts of sludge, methane gas and other byproducts of the wastewater produced by New Yorkers, as an asset — specifically, as potential sources of renewable energy options.

For the city’s Department of Environmental Protection, it is a shift. Until now, the agency has mainly played the role of water utility and environmental steward rather than energy producer.

But like other cities around the country looking to reduce both the costs of sewage treatment and disposal and the heat-trapping greenhouse gases emitted in the process, New York is beginning to look at its waste as an untapped resource.

Heating fuel can be extracted from sludge and butanol, an alternative fuel to gasoline, from the algae generated by wastewater. Sewage treatment plants could sell methane gas to generate electricity to provide power to homes. Such projects represent a more sustainable long-term approach to managing a wastewater treatment process that costs the city about $400 million annually, not including capital investments.

“There’s nothing in here that’s pie in the sky,” Caswell F. Holloway, the city’s commissioner of environmental protection, said of the plan. “While we’re early in the process, it’s real.”

New Yorkers currently produce some 1.3 billion tons of wastewater daily. The agency is seeking vendors to find uses for the resulting daily yield of 1,200 tons of sludge, a residual that is currently sent to landfills in Suffolk County, N.Y., and Virginia.

City officials, who hope to have a contract by 2013, said the solid could be harvested for gases that produce clean energy and could be used in more traditional ways, too, as fertilizer or as paving and building materials.

The biggest potential source of energy, officials said, is the methane gas from sewage treatment plants’ digesters. About half of the methane produced by the city’s plants is already used to meet about 20 percent of the energy demands of the city’s 14 sewage plants, whose electric bills run to a total of about $50 million a year. Now the city wants to market the other half, which is burned off and wasted.

Through a partnership with National Grid that is already in the works, officials said, the Newtown Creek Wastewater Treatment Plant in Brooklyn is expected to add enough methane gas to the city’s natural gas network next year to heat 2,500 homes.

City environmental officials said they were also seeking private partners to develop a plant to produce both electricity and heat or steam near its Wards Island Wastewater Treatment Plant the power would heat the plant and be sold to the market.

The agency is also studying proposals for solar and wind projects on Staten Island, including one that would place solar panels on the 200,000-square-foot roof of the Port Richmond Wastewater Treatment Plant, and another for a 1.5-megawatt wind turbine at the Oakwood Beach Wastewater Treatment Plant.

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