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Environment and Energy

Anaerobic Digesters on Central Coast turn organic waste into energy and compost

Working toward California’s legislative goal of diverting 75% of organic waste from landfills, anaerobic digesters are being put to use on the Central Coast. This technology reduces methane emissions and generates renewable energy.

Organic waste like yard clippings, food scraps and paper emit large amounts of methane gas which is a climate super-pollutant. Governor Jerry Brown signed SB 1383 in 2016 to reduce emissions by diverting 75% of organic waste from landfills by 2025.

“As a state, we have a lot of work to do to reach that 75% diversion mandate,” Kelly York said.

York is the program manager for the San Luis Obispo County Integrated Waste Management Authority. She said the county uses both a compost facility and an anaerobic digester to recycle organic waste.

“In San Luis Obispo, we have the HZI (Hitachi-Zosen Inova) facility which is an anaerobic digester next to the San Luis airport,” York said.

Landfills are also anaerobic, meaning without oxygen, but they release greenhouse gases into the air and create mountains of trash. Anaerobic digesters are enclosed, sealed systems, so the methane gas can be captured and turned into bio fuel for electricity. The remaining waste, or digestate, is dried and made into compost.

Anastasia Nicole is the Zero Waste Coordinator at California Polytechnic State University in San Luis Obispo.

“When organic material breaks down in a landfill anaerobically, it produces methane and methane is one of the most powerful greenhouses gases that we create, so by reducing the amount of food waste and organics we send to the landfill, we’re reducing our methane emissions,” Nicole explained.

She said Cal Poly sends organic waste from the campus to the anaerobic digester.

“Pre-consumer and post-consumer food scraps are scraped into carts and collected on a daily basis by San Luis garbage, our local hauler. They haul it to the Hitachi-Zosen anaerobic digester in order to make it into energy and also local compost. It’s a win, win, win,” Nicole said.

Nicole said anaerobic digester technology is not new, it’s just new to the United States.

“We’re borrowing technology that’s already been created in countries leading the way because they have less ground, Europe has less space for landfills – they’ve been dealing with this longer and they had regulations on air quality earlier than we did," Nicole said.

In 2013, Monterey County participated in a pilot program for an anaerobic digester. Tim Flanagan is general manager of the Monterey Regional Waste Management District.

“We were the first in the state of California, and only the second in the nation to have what’s known as a dry anaerobic digester located and permitted here at our facility at the Monterey landfill,” Flanagan said.

The pilot program ended in 2019 and, for the time being, the facility is back to its previous way of managing organic waste, but it’s not because the anaerobic digester didn’t work.

“Dry anaerobic digestion technology worked very, very successfully, however, the size of the facility that we had was really too small for the needs of the peninsula and the region,” Flanagan said.

Flanagan said he is currently researching options for a different system.

Santa Barbara County is just days away from turning on their newly constructed anaerobic digester at the ReSource Center, formerly known as the Tajiguas landfill.

“The anaerobic digester will be accepting organics within the next couple of weeks and it will be producing compost within about four months,” said Progam Leader Carlyle Johnston, Santa Barbara County Public Works.

Johnston said the anaerobic digester benefits the local community.

“It generates compost and it also generates renewable energy, so those two products are then used by the community. Those are benefits that have significant lowering of greenhouse gases as a community, and it also achieves the state mandates related to SB 1383,” he said.

The anaerobic digester is a large, flat-roofed building with 16 bunkers, a computer room, and air filtration system.

“Organic waste will be loaded into a bunker until that bunker is filled. Once it’s filled, the door shuts for 28 days. Before we open up a bunker, we flush it with air from the outside and if it’s got methane in it, it’s burned; any other air leftover goes to the bio filter. This captures 99% of the methane as opposed to 75% of the methane from a landfill gas collection system,” Johnston said.

The ReSource Center also has a new education area that is open to the public for tours and field trips. Posters on the walls say Reduce, Reuse, Recycle.

“What we do here at this Center is to try to mitigate the environmental impacts of our waste, but that can’t fully be done. The best thing is to not generate waste in the first place,” Johnston said.

For more information on reducing organic waste:

CalRecycle

SLO Integrated Waste Management Authority

Monterey Waste Management District

Santa Barbara Less is More

This report is made possible by a grant from the Community Foundation of San Luis Obispo County.

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