Brendan P. Bartholomew/Special to The S.F. ExaminerConstruction manager Chris Sena of Zero Waste Energy

South City sanitation collector to begin fueling trucks with converted food waste

The South San Francisco Scavenger Company is taking an innovative approach with its new processing facility that will convert some of the food scraps it collects into fuel for its garbage trucks.

When the new system begins operating, much of the organic waste currently being hauled to a South Bay facility will instead be converted on-site in South San Francisco into compressed natural gas, which will in turn fuel the sanitation service provider's collection vehicles.

This change comes as the company rolls out a full residential food composting program for the communities it serves. Up until now, residential customers in South San Francisco, Brisbane and Millbrae were only asked to put their yard waste in compost bins, while commercial customers such as restaurants, hotels, and San Francisco International Airport have already been separating their food waste.

In a recent tour of the South City facility, company President Doug Button explained the new waste conversion process. The food waste is loaded into a building that looks like a small, nondescript warehouse on the outside, but with one distinction: the roof inflates like a balloon as bacteria inside slowly digest the garbage and turn it into natural gas. The process is begun by the naturally occurring bacteria that comes with the waste, and then moved along by air pumps, heating coils, and anaerobic bacteria similar to the kind used in wastewater treatment facilities, Button described.

The gases are then routed to an adjacent collection of pipes and equipment resembling a small oil refinery. Butane and propane gases are extracted and used to generate electricity for the system's heating coils. Meanwhile, the main natural gas product is prepared for use by the company's truck fleet.

The scavenger company is phasing out its diesel-powered garbage trucks, and will eventually have only natural gas-powered trucks in its fleet. Button noted that vehicles running on natural gas supplied by oil companies have lower carbon footprints than diesel-powered trucks.

However, the carbon-intensity rating the federal government assigns to trucks running on natural gas produced from compost is so much lower than either of those options that it's expressed as a negative number, Button said.

While the system is projected to produce the energy equivalent of 120,000 gallons of diesel fuel per year, Button said he doesn't expect it to completely pay for itself. However, he noted that beyond fuel cost savings, the environmental benefits will include reduced reliance on natural gas obtained through hydraulic fracturing (fracking) or other oil industry processes.

Another sustainability benefit will be dramatically reducing the amount of waste deposited in landfills, Button said, explaining that buried organic waste is a source of methane, a greenhouse gas that contributes to global warming.

bbartholomew@sfexaminer.com

Bay Area NewscompostDoug ButtonPeninsulaSouth San Francisco Scavenger Company

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