Cooking up alternatives
California city converts restaurant waste into power source.
For the past two years, Riverside, Calif., has been feeding restaurant grease into the digesters of its cogeneration plant to produce electric power. The digesters convert the grease into enough methane gas to operate two of the city’s three cogeneration engines around the clock, generating an average of 1.5 to 1.7 megawatts of power.
Riverside launched the project after sharp increases in private waste disposal fees made it financially difficult for local restaurants to have their grease waste interceptors pumped regularly. If interceptors became overloaded, they would discharge restaurant grease waste directly into the sewer collection system, clogging up entire sections of pipeline.
Regan Bailey, a wastewater resources analyst for Riverside’s public works department, spearheaded the grease-to-power project, initially using a $16,000 Public Benefits Grant from Riverside Public Utilities. The grant, funded from a state-mandated charge on customer electric bills, is designed to promote energy efficiency and conservation or investment in renewable resources.
The project was immediately successful, consistently producing 30 percent more methane gas from a single gallon of restaurant grease than average estimates. It also has reduced the plant’s use of natural gas, which is needed to heat cogeneration fuels to produce electrical power. “We have found that restaurant grease actually has a much higher BTU content than other cogeneration fuels, such as tree waste,” said David Wright, general manager of Riverside Public Utilities.
Riverside plans to purchase a fuel cell this year to boost cogeneration electricity production to 3 megawatts, enough to power the city’s wastewater treatment plant. City officials estimate the system will save more than $1 million a year in electricity and natural gas costs. And, for local restaurants, the cost of pumping grease waste interceptors has fallen by 50 percent, from 20 cents to 10 cents per gallon.
— Jeff Crider, a Riverside, Calif.-based freelance writer
Project: Grease-to-power pilot project
Agency: Riverside, Calif. Public Utilities
Vendors: Aliso Viejo, Calif.-based Fuel Cell Energy, and Littleton, Colo.-based Alliance Power
Date began: April 2005