With the fossil fuel era coming to an end soon, there are frantic efforts all over the world to find alternative energy sources so that there is no major hiccups in the present way of living in this planet. Energy from sustainable sources like sun, wind, ocean, geothermal, nuclear and others are in advanced stages of becoming economically viable soon. In this relentless search for energy, one source being ignored is the perpetual availability of sewage in thousands of urban areas which contain recoverable energy through appropriate technology and investments. The UK seems to have taken the lead by installing sewage derived energy systems in the city of London which is reported to be generating enough power, accounting for 14% of the power needs of the area and saving $ 23 million annually in electricity bills from the conventional suppliers
"Sludge, the solids that remain after sewage has been cleaned into effluent, has a high B.T.U. content (a measurement of fuel's energy); it burns efficiently and well. Other aspects of wastewater treatment can also reap energy: anaerobic digestion (whereby bacteria munch on the organic contents) produces methane, which with turbines can become combined heat or power. Microbial fuel cells can use bacteria to get electricity from sewage, while gasification, a high-temperature process, can reap fuel-ready gas from sludge".
The US with about 16000 sewage treatment plants does not produce any power for use, though about 1000 of them with daily supply of more than 5 million liters of sewage could generate viable quantity of power. Already 544 of them are producing enough methane through anaerobic digestion just to be flared out. This could have generated about 340 MW energy sufficient to power 0.34 million houses, off setting emission of 2.3 million tons of green house gas emission equivalent to creating a 0.64 million acres of forest!. Probably the force of circumstances may still persuade that country to go for sewage power in the near future. As for India, no data is available about the number of captive sewage plants in working condition that could be candidates for producing energy.