Another way to save energy in the water supply
process is by retrofitting wastewater facilities with
Combined Heat and Power (CHP) systems. CHP
systems can recover biogas (a mixture of methane,
carbon dioxide, water vapor, and other gases)
from anaerobic digesters to heat buildings or to
generate electricity. For example, San Francisco’s
East Bay Municipal Utility District captures
and uses biogas to generate enough electricity
to cover 90 percent of energy needed at its main
wastewater facility. It is estimated that if all 544
large sewage treatment plants in the United States
operating anaerobic digesters were to install CHP
systems, about 340 megawatts of clean energy
could be generated, offsetting 2.3 million metric
tons of CO2
emissions annually—equivalent to
planting about 640,000 acres of forest, or the
emissions of about 430,000 cars.7