California city converts organics into renewable fuel for solid waste trucks

The city of Roseville, California, has launched an initiative to decrease greenhouse gas emissions and minimize landfill waste by powering its trash and recycling truck fleet with renewable natural gas (RNG) derived from digesting organics. 

The city hired Brown and Caldwell, an environmental engineering and construction services firm headquartered in Walnut Creek, California, to design a renewable biofuel production facility as part of the local wastewater treatment plant expansion. The Pleasant Grove Wastewater Treatment Plant is owned and operated by Roseville and treats millions of gallons of wastewater every day. The plant already supplies more than half of the 1 billion gallons of recycled water the city delivers annually for landscaping and industrial purposes. Since 2020, the plant has been undergoing renovations to increase treatment capacity from 9.5 million gallons to 12 million gallons of wastewater per day. Part of this expansion is the energy recovery project led by Brown and Caldwell that will transform the plant into a waste-to-energy facility capable of producing RNG fuel.  

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Richard D. Plecker, Roseville’s environmental utilities director, says, “We have come full circle with managing our integrated utility service to benefit our community. Through this project, we have the opportunity to generate environmentally beneficial byproducts, mitigate the impacts of climate change, comply with regulatory obligations and safeguard the interests of our ratepayers by stabilizing fuel costs for our solid waste fleet.” 

The city has installed two new anaerobic digesters at the plant to stabilize wastewater solids generated in the treatment process, which in turn creates a sustainable fuel source. A receiving facility has been constructed to accept high-strength organic materials, such as fats, oils and greases, directly into the anaerobic digesters. This maximizes digester gas production for RNG conversion and diverts up to 12,000 tons of high-strength organic waste per year from landfill. Four microturbine cogeneration units produce electricity to help power the gas conversion process and provide heat for the anaerobic digesters. 

By running its solid waste collection fleet of approximately 47 trucks via a new on-site RNG fueling facility and ceasing diesel use, the city says it will reduce greenhouse gas emissions by about 7,716 tons of carbon dioxide equivalents per year, equal to planting more than 270,000 trees. Because this project also will lower nitrogen oxide emissions by approximately 5 tons per year, the city will earn credits through the Low Carbon Fuel Standard. Additionally, by generating electricity with microturbines, the project is eligible for the Clean Water State Revolving Fund Green Project Reserve, which incentivizes projects that address water or energy efficiency and reduces costs for utility customers.