Wastewater Treatment Plant to Produce Fuel for City Vehicles

With transportation the largest contributor to greenhouse gas emissions in California, San Mateo will be the first city to reduce emissions by using biogas produced at its wastewater treatment plant for use in city vehicles.

4 minute read

December 21, 2015, 1:00 PM PST

By Irvin Dawid


San Mateo broke ground Dec. 11 "on California’s first city-run biogas conversion project to produce compressed natural gas (CNG) at its wastewater treatment plant," writes Samantha Weigel for The Daily Journal. The primary purpose of the project, in addition to producing "the biofuel equivalent of 500 gallons of gasoline every day," is to increase the city's sustainability by reducing greenhouse gas emissions, adds Weigel.

"It’s definitely part of our Climate Action Plan [184-page PDF] and sustainability goals to switch from gas engines and diesel engines to alternative fuels," The effect of using the byproduct is we can utilize it instead of burning it off or essentially wasting it,” said Public Works Director Brad Underwood.

Furthermore, by purchasing at least 50 new clean natural gas vehicles — likely pickup trucks for the Public Works as well as Parks and Recreation departments — the city will become less reliant on traditional fuel. As vehicles are the number one contributor to the city’s greenhouse gas emissions, this project supports long-term environmental initiatives.

Weigel emphasised that point in a January piece on the city's Climate Action Plan:

San Mateo’s largest greenhouse gas emissions generators are vehicles, making up 58 percent of its total. Approximately 35 percent is attributed to commercial and residential energy consumption and 3 percent comes from solid waste, according to Pacific Municipal Consultants.

Greenhouse gas emissions are reduced in two ways with the new project:

  • "Typically, the plant just burns off the biogas that’s created as part of the treatment process at the facility that accepts wastewater from San Mateo, Foster City, Hillsborough, Belmont and unincorporated portions of the county," writes Weigel, though she adds some burning will continue after the project is completed as not all biogas can be captured.
  • Biogas, a renewable or biofuel, has the lowest "carbon intensities" of any transportation fuel according to the Low Carbon Fuel Standard Program of the California Air Resources Board (CARB).

San Mateo received a $2.45 million grant from the California Energy Commission "to construct a digester that will capture underutilized biogas, which naturally occurs while treating wastewater, and turn it into compressed natural gas (CNG) that will be used to fuel new city-owned vehicles," writes Weigel. It "includes a distribution system that serves like a pump at a traditional gas station." Total cost is nearly $5 million.

Greenhouse gas emissions are reduced in two ways with the new plant.

  • "Typically, the plant just burns off the biogas that’s created as part of the treatment process at the facility that accepts wastewater from San Mateo, Foster City, Hillsborough, Belmont and unincorporated portions of the county," writes Weigel, though she adds some burning will continue after the project is completed.
  • Biogas, a renewable or biofuel, has the lowest "carbon intensities" of any transportation fuel according to the Low Carbon Fuel Standard Program of the California Air Resources Board (CARB).

CARB has a rating for "Landfill gas (bio-methane) cleaned up to pipeline quality NG; compressed in Calif." (11.26), and "Dairy Digester Biogas to CNG (13.45) per its rating table (PDF). By contrast, gasoline has rating of 95.86.

Apparently, biogas from wastewater treatment plants has yet to be rated. CARB was contacted to see if they will do so.

The only other fuel that comes close is biodiesel: "Conversion of waste oils (Used Cooking Oil) to biodiesel (fatty acid methyl esters -FAME) where “cooking” is not required" (11.76).

Using the energy potential in biogas is nothing new for wastewater treatment plants (WWTPs), but only a minority of them use the biogas as a transportation fuel. According to the Department of Energy's Alternative Fuels Data Center on "Renewable Natural Gas (Biomethane) Production:

There are more than 16,000 WWTPs in the United States, and about 1,500 employ anaerobic digestion to produce biogas that is used on site. The Janesville Wastewater Treatment Plant in Wisconsin is an example of a plant that uses biogas to produce RNG for use in vehicles.

"It really adds up in terms of carbon reductions that the city gets from this," proclaimed Mayor Joe Goethals.

It’s carbon that would otherwise just be admitted into the atmosphere and instead we’re using it to offset the gasoline that our fleet would otherwise use. So it’s a very exciting project and we’re glad to be the model for the state on this,” Goethals said.

"Anticipating completion is in August, (2016)" adds Weigel.

Friday, December 11, 2015 in San Mateo Daily Journal

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