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Food to Energy program is a first in Marin

The two digesters at CMSA is where food scraps are converted into biogas
The two digesters at CMSA is where food scraps are converted into biogas
- By Rem O'Donnelley

The Central Marin Sanitation Agency (CMSA) opened their doors to guests Tuesday to show off their landmark renewable energy project. After several years in the making they are able to convert food into energy.

At the The Food-to-Energy (F2E) program tour it was announced that this is the first program of its type in Marin County and only the second in the state where a wastewater treatment plant is using food scraps to create energy through anaerobic digestion. The F2E program is based on a public and private partnership. The public half is the CMSA and the private half is the Marin Sanitary Service (MSS).

The process started six years ago said Christina Heartquist, a public relations representative for Marin Sanitary Service. “The first thing they had to do was a methane feasibility study to see how it would affect methane production. It all started with that study. After that it was a lot of permitting, PG&E gave them a grant to do this because there was a lot of new equipment that had to be built. It was a long process until earlier this year when the pilot program began and Marin Sanitary Service began outreach and cold calling businesses asking if they had enough food scraps and wanted to be part of this program,” she said.

Food waste from grocery stores, caterers and restaurants is collected in a special truck that takes it back to the MSS transfer station in San Rafael. After being inspected for foreign contaminants, (including gloves and plastics) the food is ground into pieces no larger than one inch. The pieces are then loaded into a transfer container.

A truck takes the container one mile East to CMSA for the remaining steps. The ground food is dumped into a tank and grease is added. It is then filtered before going to a paddle finisher. Finally the food mixture is pumped into two large, concrete tanks called digesters. It is inside these tanks that a series of microbes break down the mixture and eventually release biogas. The methane biogas gas is pumped into a filter to purify it before the fuel is run through a generator to create renewable electricity that is used at CMSA.

The two digesters can hold one million gallons of processed material. This material includes both waste received from sewage as well as from food scraps. “We can process all the waste water solids in one digester. When we run both of them at the same time we have enough capacity to receive about 109 tons of commercial food waste and we're receiving about three and a half tons per day, so we have a lot of extra capacity,” Jason Dow, President of the CMSA Board said.

He explained that currently the biogas is powering approximately 70 to 75 percent of the plant's power. They hope to collect more food scraps and generate more biogas within the next two years. They hope to be able to export some of the generated electricity with utility companies. “It's looking really great for us, we're ahead of the game of the point we thought we'd be at this point now,” he said.

“This has been an amazing six years for the agency, because we're really excited about this partnership we have with Marin Sanitary Service from early 2006 when this whole concept was hatched,” Dow said.

There are additional benefits than just generating electricity. The plant means that 27 percent of food scraps are diverted from the landfill. This means that there are fewer truck trips to the landfill. This reduces greenhouse gasses and less traffic on the road with these trucks and these are all good things.