Fuel cells are electrochemical devices that convert the energy released in chemical reactions directly into electrical energy (direct current [DC]). The process occurs without combustion, thereby producing electricity through a virtually emission-free process. The reaction between hydrogen (derived from natural gas, methane, propane or anaerobic digester gas) and oxygen produces DC power and water. The DC power can then be converted to alternating current (AC) power by use of an inverter.
Fuel cells can use waste products (anaerobic digester gas—a byproduct of wastewater treatment—and landfill gas—methane) to produce power and eliminate pollution caused by burning waste gas. Flaring, or burning the gases, creates ozone precursors such as nitric oxides and volatile organic compounds, but even if the gas is not burned, it contributes significantly to the greenhouse effect, since methane traps 10 to 20 times more heat than carbon dioxide. That is why wastewater treatment plants (particularly those in heavily urbanized areas such as New York City) are regulated as stationary sources of air pollution under the Clean Air Act. Landfills, which also produce and flare methane gas, are another candidate for this technology.
Fuel cells also have the advantage of running indefinitely as long as fuel (hydrogen and oxygen) is supplied, making them the perfect candidates for on-site generation.