Turning Sewage Gas Into Electricity and Heat
by Andrew Revkin, New York Times, February 7, 1999
Sewage treatment plants purify water, but they also foul the air, with plumes of methane and sulfur and nitrogen oxides, which smell bad and contribute to smog and global warming. Now, a sewage plant here is turning its unwanted gas into electricity and heat. The only byproduct, officials say, is hot water. The new fuel-cell system, the first for a sewage plant in North America, has proved to be effective after a year of operation, officials from the New York Power Authority said. The system generates 200 kilowatts of electricity, enough to supply 60 typical homes, the officials said.
In the process, more than 20 tons of gas that would otherwise have simply been burned off in the open air or wafted away was turned into electricity last year, said Shalom Zelingher, the director of research for the Power Authority. The hot water generated was used to warm bacteria that help break down the sewage. "This is not just a concept anymore," he said. Fuel cells run on hydrogen, which is contained in standard fossil fuels like natural gas and gasoline, and also in methane. They produce no significant pollution because they use a chemical reaction to harvest energy from the fuel without burning it, Zelingher said. The same process supplies electricity on the space shuttle and is finding more uses each year on Earth, with fuel cells powering vehicles, factories and, in a few weeks, the New York Police Department precinct house in Central Park. Two fuel cells will turn natural gas into electricity at the office tower at 4 Times Square. Others are going to be installed in some city hospitals to provide uninterrupted power during blackouts, Power Authority officials said.
But some of the biggest benefits come at a sewage plant, officials said, where the system uses waste methane, which is abundant and free, instead of natural gas or some other fuel that must be bought. The systems can also be run with gas from landfills. New York City environmental officials recently inspected the Yonkers system and said they hoped to install fuel cells at some of the city's 14 sewage plants, in hopes of recycling some of the 1.6 billion cubic feet of gas generated every year. Most of that gas is now burned off in flares at the plants. Joel A. Miele Sr., the city's Commissioner of Environmental Protection, said the device would be particularly welcome at plants that have been plagued with odor problems from the excess gas. "Sometimes our plants can be very, very unwelcome neighbors," Miele said.
When engineers from the Power Authority presented their results with the fuel cell, he recalled, "It sounded like Santa Claus had come early." Fuel cells have been around for decades, but because of their high price and complicated technology they have been relegated until recently to exotic applications like the space program. Within the devices, a chemical process causes hydrogen from the fuel and oxygen from the air to combine, making water and releasing electrons. The electrons flow across plates like those in a car battery and generate electricity. The Power Authority supplies electricity to public agencies, powering everything from sewage plants and the New York City subways to hospitals, schools and public housing. It has been developing alternative power sources to cut the need to build costly new power plants in the region, said Stephen Schoenholz, a spokesman.
The fuel cell in Yonkers is a standard commercial 200-kilowatt unit made by the ONSI Corporation of New Windsor, Conn., which also makes the fuel cells for the space shuttle. But the Power Authority, together with federal environmental scientists, devised an additional filter that first removes impurities from the waste gas, like sulfur and nitrogen, that could damage the device. The system costs $1.3 million, but that price should drop as the technology becomes more established, company officials said. The fuel cell test in Yonkers was partly supported by money from the Department of Energy, New York State, and Westchester County, which runs the sewage plant, Schoenholz said. The Yonkers plant, which handles more than 90 million gallons of wastewater a day, has for many years used about half of the methane as fuel for boilers and some engines, said Thomas Lauro, the deputy director of wastewater treatment. Even though the staff plans to exploit more of the gas to power machinery, it is unlikely they will be able to find a use for all of it so a second fuel cell could eventually be installed, he said.
Federal energy officials say one of the greatest benefits of using a fuel cell at a sewage plant or landfill comes from consuming methane, a gas that otherwise contributes significantly to the growing greenhouse effect. Methane, carbon dioxide and other "greenhouse gases" prevent the heat from the sun from readily escaping from the atmosphere into space. As levels of these gases increase, the planet's average temperature is expected to continue warming, scientists say, raising sea levels and shifting patterns of droughts and floods. "It's a real two-fer," said Dan W. Reicher, the Assistant Secretary of Energy for energy efficiency and renewable energy. "It's a global warming gas that you can put to good use as a clean power source." And it's free, he added.