SMUD co-digestion facility under construction

By Anna Austin | April 12, 2012

The Sacramento Municipal Utility District and the Sacramento Regional County Sanitation District have begun construction of a co-digestion facility at the Sacramento Regional Wastewater Treatment Plant in Elk Grove, Calif.

The new facility will accept fats, oils, greases and liquid food processing waste, and will include a receiving station with two 15,000-gallon storage tanks, according to Jose Ramirez, SRCSD senior civil engineer. “It will have a couple of inclination ports for loading decks that trucks will be able to pull into, and a connection port on each tank to allow the discharge of waste into the tanks,” he explained.

Inside, the tanks are mechanisms that will mix the material, which will be preheated until it is ready for transfer into the digesters, according to Ramirez. There, it will increase the amount of biogas already produced at the plant, enough to generate power for around 2,000 homes, or 1 to 3 MW.

Any leftover digester material will be sent to a storage pond where solids from the wastewater treatment process are harvested, and 20 to 25 percent will be sent to an on-site biosolids recycling facility that produces Class A biosolids pellets sold to local farmers.

Although the facility already has an existing fats, oils and grease disposal program, Ramirez said the only materials accepted now are those generated within Sacramento County. “As part of the biogas enhancement project, we will be lifting the out-of-county probation to allow more materials to come into our service area,” he said. Liquid waste haulers are not contracted for their waste, according to Ramirez, but in order to dispose at the site, they must request a permit from SRCSD to discharge into the system.

Construction of the facility should be completed by the end of this year, Ramirez said, with full operations to begin about a year from now. “Depending how it goes, we may consider accepting food waste in the future.”

The total cost of the project will be about $2.1 million. SMUD and SRCSD received $1.45 million in Recovery Act funds and $100,000 from the California Energy Commission to help cover construction costs.