They prefer to call it wastewater, but the bottom line is that researchers at the University of Nevada are close to commercializing a process for generating renewable energy from sewage sludge. The energy could be used to run equipment at the plants, which is a big deal because sewage treatment plants (okay, so wastewater treatment plants) are massive energy consumers. Operations like pumping and aerating, skimming off trash, separating grease, drying sludge, and disposing of sludge have a huge carbon footprint, especially when you get into big-city treatment systems that handle hundreds of millions of gallons daily.
Nationwide, that activity adds up millions of tons of greenhouse gases which could be neutralized by sewage-to-electricity technology. It could also help reverse the relationship between cities and energy; they will produce a good chunk of the energy they use instead of importing it, using wastewater treatment plants and other infrastructure as inexpensive clean energy generators that help keep local budgets manageable while reducing air pollution and greenhouse gases.