Retrofit facilitates food waste composting

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Courtesy of BioCycle Magazine

Waste Connections, Inc. (WCI), the third largest waste and recycling company in North America, recently invested $10 million to upgrade Silver Springs Organics (Silver Springs), a commercial composting facility in Washington State that it purchased in 2009 from Greg Schoenbachler, Silver Springs’ founder. The facility, located in Rainier, opened for business in April 2007 (see “Creating An Affordable Road To Composting,” October 2007). Schoenbachler hired Seattle-based Engineered Composting Systems (ECS) in June 2006 to help him design and build the initial composting facility.

Local regulations in Thurston County where the original Silver Springs operation was sited require recycling and composting facilities to operate under a roof to minimize wastewater and odor generation. This meant constructing a very large building, which would have been too expensive for a start-up merchant facility without long-term contracts. Schoenbachler proposed using the ECS AC Composter for the original facility, which uses impermeable covers over the compost piles, as a cost-effective alternative to a roof. In addition to the covers, the system had three major components: automated aeration control and monitoring; a negative-only aeration system; and a biofilter for odor and emission control.

Silver Springs filed for a variance from the Thurston County code on the basis that the AC Composter cover and negative airflow system together could capture and contain the odors and ammonia emitted by the composting process, thereby meeting the code’s intent. All of the process air would also be scrubbed through biofilters. The county granted the variance to build an open-air, covered ASP. Above-ground aeration was utilized instead of a more expensive below-grade aeration floor. “The way the code was written, aeration wasn’t required,” recalls Schoenbachler.

When Silver Springs opened in 2007, it was permitted to process 10,000 tons/month of pre and postconsumer food waste, as well as yard trimmings, wood and agricultural feedstocks. Selling the facility wasn’t in Schoenbachler’s plans when he started. “I wasn’t anticipating selling it,” he says.” “Waste Connections was one of our customers and approached me because they needed additional composting infrastructure as part of their system.” After acquiring Silver Springs, WCI retained all the staff including Schoenbachler, who became site manager.

At the time of the sale, the amount of organics coming into the facility was increasing dramatically, which led to odor problems from the leachate on the paved surfaces and in the pond, and from low oxygen levels within composting materials due to insufficient aeration — attributed to the higher volume being processed. “Some changes in local food and yard waste collection programs created exponential increases that outpaced the infrastructure that was in place,” explains Schoenbachler. “We could have made modest improvements and struggled with the volume threshold, but Waste Connections saw that an overhaul was the best long-term solution.” WCI shut down the facility in August 2011 to undertake major facility improvements. While the facility was closed, the feedstocks were diverted at the source to other composting facilities.

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