Deer Island, Boston Harbor

In the U.S., anaerobic digesters are being used in a number of wastewater treatment plants, such as the Deer Island facility in Boston Harbor. The digesters are the egg-shaped vessels on the left, which convert sewage into biogas that's burned on-site for heat and electricity. The co-generation facility saves the Massachusetts Water Resources Authority (MWRA) $15 million a year in fuel costs. The MWRA has also put up wind turbines and solar panels.