What to do with human waste is one of the more vexing problems of industrial society. Even when the waste is treated, the pollution it generates remains a problem, not the least of which is what happens as it naturally decomposes.
Not only does decomposing fecal matter generate an unpleasant stench, it pollutes the air. Human feces are broken down by anaerobic bacteria. As they digest the waste, the bacteria release methane gas, one of the well-known greenhouse gases. Traditionally, wastewater treatment plants handled this one of three ways: they released the gas into the atmosphere, burned it with flares, or siphoned it off to power gas turbines.
Many cities in California, where anti-air pollution laws are strict, are rejecting all of these options in favor of turning wastewater into clean energy. This energy helps run the sewage treatment plants, drastically reducing their need for power from the grid.
The technology that makes this possible is fuel cells. A fuel cell creates electric current by mixing hydrogen fuel with oxygen from the air. In that respect, it is similar to a battery. Batteries also generate electricity by means of chemical reactions. However, unlike a battery, a fuel cell must have its chemical reactors - that is, its fuel - constantly fed to it. In that respect, it is like a fire, which can keep burning only as long as it has fuel. Unlike a battery, a fuel cell has to stay connected to its energy source to work.
Fuel cells can use many kinds of gas to generate electricity. Methane from biodegrading substances is one. Fuel cells can also run on natural gas and industrial waste gases. And fecal matter is not the only biodegrading substance that generates usable gas.
Sierra Nevada Brewing Company in Chico, California uses fuel cells to turn wastes generated by the beer making process into electricity to run the brewery. The Sheraton San Diego Hotel uses the same technology not only to generate electric power, but to heat three swimming pools. Fuel cells operating on biogas are being looked at as a way to provide cheap, clean, and easily accessible power in remote rural areas across the nation.
Not only does using wastewater to power fuel cells spare the air from methane gas, fuel cell electricity is one of the cleanest types known. Its carbon dioxide emissions are so low that fuel cell energy production is exempt from many environmental protection regulations designed to reduce greenhouse gas. Fuel cells, by their very nature, meet a higher environmental protection standard than is even remotely possible with fossil fuels.
While fuel cell technology has existed for over a century, only recently has it become affordable enough for municipal wastewater treatment plants to use it. In light of their benefits, fuel cells are well worth the cost. If the world follows the example of many California cities, the most common energy source of the future may well be wastewater.
Sources:
http://www.altenerg.com/back_issues/index.php?conten t_id=81
http://www.energy.ca.gov/process/pubs/ebmud.pdf
http://www.sustainablebusiness.com/index.cfm/go/news .display/id/19505
http://www.energy.ca.gov/process/pubs/fuelcell.pdf