![]() ![]() “A top official for the General Services Administration, which will act as the property manager for the building, initially said the judges wouldn’t move in until the last bit of sawdust was swept up. The city also fretted over delays that were costing the city $10,000 a day in getting the courts moved in and upsetting the fiscal balancing act of the bond interest payments. While BioCNG’s units have been employed at several landfills in the Midwest, the Sacramento biodigester is the first project for the company using an organic food waste digester.It was a slog to get to the finish line, and not without a fair share of drama, including a prediction of cost overruns due to cleanup of pollutants found on site and changes in the design requested by federal judges and GSA. ![]() According to Atlas, the fuel costs about $2.25 per gallon. Currently CNG powers about one-fourth of Atlas Disposal’s vehicles, including waste recycling trucks. At this level, the system is expected to be capable of producing around 1,500 diesel gallon equivalents per day from the digester biogas, according to BioCNG.Ītlas Disposal also has opened California’s first AD-based renewable natural gas fueling station, which uses natural gas produced at the recycling facility to fuel the company’s fleet as well as other area vehicles running on compressed natural gas (CNG). Clean World Partners began expanding the facility in 2014 to allow the facility to accept 100 tons per day of food waste. Through anaerobic digestion (AD), the food waste is converted into renewable natural gas, electricity and heat, with material remaining from the process being turned into fertilizer and soil amendments. The Organic Waste Recycling Facility at the South Area Transfer Station (SATS) in Sacramento, Calif., began accepting 25 tons of food waste per day in December 2012, collected by Atlas Disposal Industries from area food processing companies, restaurants and supermarkets. The system initially used about 100 cubic feet per minute of biogas from the food waste digester to produce about 450 diesel gallon equivalents of CNG fuel per day. Meanwhile, in Sacramento, food waste is being converted to CNG with the help of a high-solids anaerobic digestion system from Clean World Partners, Gold River, California, and an alternative vehicle fuel conditioning system from Madison, Wisconsin-based BioCNG. The next step in this program is a co-digestion pilot study, currently under way, in which pre-processed SSO is added to the digesters. This approach requires preprocessing the SSO materials so they can be mixed with the sewage sludge without creating upsets in the digester. Similar co-digestion systems have been implemented in several cities across North America, using excess sewage sludge digester capacity. The conclusion was that co-digestion with the City’s sewage sludge, using excess digester capacity available in the city’s wastewater treatment plant, would be the most beneficial method for processing the commercial organics, and would result in a net-zero economic result for the City. Costs included all capital costs, including not only the digesters and biogas-to-CNG conversion, but also the costs for 50 new CNG-fueled trucks.Įnvironmental and social factors were also considered in a “triple-bottom line” analysis. ![]() Revenues included fuel cost displacement for the city’s refuse trucks, which, appropriately, would be fueled by the resulting CNG. Concept designs, life-cycle costs and revenues were prepared for all the alternatives, including operating costs over the project lifetime. The city then proceeded to evaluate the best alternatives for processing the SSO, which included several methods of anaerobic digestion and composting by combining with yard waste. This thorough bottom-up study identified what could actually be collected, rather than what might be generated based on business types and other information. The results of several surveys of businesses in the city and a pilot collection program indicated that approximately 3,300 tons per year of SSO suitable for producing biogas could be collected. The city decided to focus on commercial sources (stores, food processors, restaurants, etc) rather than a separate program for residential SSO, in addition to the yard waste program, as other cities have done. The evaluation began with characterization of the feedstocks that could be collected in the city. In 2012, the City of Tacoma began evaluating different options for collection and processing source separated organics (SSO), in addition to the yard waste collection and composting program that it has provided to citizens for years. ![]()
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