The Sacramento Regional Wastewater Treatment Plant has formed partnerships for cogeneration and for grease collection to boost biogas production.
The Sacramento Regional Wastewater Treatment Plant in Elk Grove, Calif., thrives on partnerships. Among these is a program that treats imported fats, oils and grease (FOG) to increase production of biogas for an on-site cogeneration plant.
Owned and operated by the Sacramento Regional County Sanitation District (SRCSD), the plant treats wastewater for 1.4 million residents and leases part of its land for the cogeneration plant, a biosolids recycling operation and a firm that manufactures ice.
The FOG program was launched earlier this year in an effort to improve sustainability. Jose Ramirez, senior civil engineer, says the improvements go along with a new FOG receiving station called the Biogas Enhancement Facility (BEF).
The idea came from discussions that started in 2006 between SRCSD and the Sacramento Municipal Utilities District (SMUD), the local electric company, about biogas production by direct injection of FOG into the anaerobic digesters.
“We started with a planning-level feasibility study that proved it was technically feasible and recommended a small-scale pilot project,” says Ramirez. The two agencies then co-funded a pilot project. The results were positive, and the agencies agreed to move forward with a full-scale project.
As luck would have it, the decision to make a large capital investment came at the same time the federal government made available billions of dollars in stimulus funding through the American Recovery and Reinvestment Act of 2009. Facing a $3.5 million overall cost, the SRCSD/SMUD partnership garnered $1.45 million in stimulus funds and $100,000 in matching funds from the California Energy Commission.
Construction and initial testing of the facility was completed in December 2012. The plan came with a challenging completion schedule. “Everyone worked really hard to assist the contractor in expediting submittal reviews and process access requests to move the project along,” says Gerardo Aguirre, associate civil engineer and project engineer. It was designed and completed in about 20 months.
The new FOG receiving station keeps commercial FOG out of the collection system and treatment process. This allows for more efficient treatment and disposal and reduces the risk of collection system backups. The facility was designed to process up to 42,000 gallons of FOG per day.
“Before this, FOG was processed through the plant’s primary and secondary treatment process,” explains Ramirez. “Those processes lose much of the energy available from the FOG. We see a direct benefit to energy production and operations and maintenance by removing the FOG from the treatment processes.”
Area haulers and FOG producers, such as restaurants, benefit because they no longer have to ship grease to out-of-county facilities. That saves on transportation costs, and the fees they pay to SRCSD are competitive. “We had a policy that we wouldn’t accept any FOG from outside Sacramento County, so some FOG was being trucked to distant facilities in the Bay area,” says Ramirez. “With the new facility, we now accept FOG material from outside of Sacramento County.”
Haulers unload directly to the BEF, and the FOG is added directly to the mixed sludge loop that feeds the digesters. This direct injection to the digesters will break down FOG more efficiently and produce more biogas.
“For the last few years, we were getting about 10,000 gallons of FOG per day,” Ramirez says. “We’re expecting ultimately to get as much as 30,000 to 40,000 gallons per day.” Haulers are not required to secure a contract with the wastewater treatment plant, but they must obtain a permit.
FOG digestion paying for itself
The tipping fee for haulers is one of the main revenue sources for the FOG program, designed to fully fund operation and maintenance and pay off SRCSD’s investment of just over $2 million.
Biogas produced at the wastewater treatment plant is piped next door to the 100 MW Carson Energy cogeneration plant, operated by SMUD on property leased from the SRCSD. The biogas is also delivered to SMUD’s Cosumnes Power Plant in southern Sacramento County. The additional biogas from the new BEF is enough to provide electricity for up to 3,000 homes a year.
In exchange, the wastewater treatment plant receives process steam for facility heating and to maintain its digesters at the optimum 95 degrees.
The wastewater treatment plant is one of the largest producers of biosolids in California, processing 26,000 dry tons a year. Thirty percent of the biosolids — 20 tons per day on average — is pumped from the anaerobic digester to an on-site biosolids recycling facility owned and operated by Synagro. It was the first biosolids recycling operation in California when it was established in 2004.
It treats biosolids to Class A standards through dewatering, heating and drying. The resulting pellets, 7,500 dry tons per year, are sold to the local agricultural community, producing a small stream of revenue for Synagro. In the near future, Synagro may partner with a local fertilizer manufacturing firm to produce a bagged fertilizer product that can be sold at home improvement stores.
The remaining 70 percent of biosolids are pumped and treated at 20 on-site lagoons. They remain there for three to five years until harvested and land-applied on three sites on the plant property, covering about 120 acres.
The BEF has been a sound investment for both SRCSD and SMUD. It is expected to improve treatment plant efficiency, increase biogas production, provide a more affordable option for managing FOG and reduce greenhouse gas emissions from transporting FOG to more distant sites.