More than 100 semi trucks enter the back gate of the Oakland, Calif., wastewater treatment plant every day, carrying tons of unusual and often disgusting freight: tons of cheese whey, chicken blood and heads, used cooking oil. And yet wastewater director Bennett Horenstein enthusiastically welcomes it. It is, after all, free fuel.
Machines pulverize the cargo to the consistency of applesauce, then pipe it to 12 massive tanks called anaerobic digesters. Inside, bacteria devour it, along with solids from the plant's sewage, producing methane-rich biogas that is captured and burned to generate electricity – effectively making the facility a renewable power plant.
Before, sewage provided only enough biogas to supply half the treatment plant's electricity. Now, with the trucked-in waste, the plant's production has more than doubled, covering its own needs and generating enough extra power for the equivalent of 1,250 homes.
Driven by rising electricity costs and California's mandate to draw 33 percent of its power from renewable sources by 2020, wastewater treatment plant managers across the state are following Horenstein's example, learning how to cut costs while reducing greenhouse gas emissions.
"The entire industry is looking (at) what we've done here," says Horenstein. Eventually, he also hopes to recover nutrients for agricultural fertilizers and larger quantities of useable water from the plant's sewage stream. "In 20 years, wastewater treatment plants will be valued for all the resources they produce."