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<br /> <br /> <br />ADDITIONAL INFORMATION: <br /> <br />Credit: CR&R Environmental Services Credit: American Biogas Council <br />Anaerobic digestion (AD) uses anaerobic bacteria to digest the organics in the absence of oxygen (in a <br />completely closed system) and produce methane (similar to the process that produced fossil natural gas millions <br />of years ago) plus CO. After the digestion, there remains a liquid and solid digestate full of high quality nutrients <br />2 <br />useful as compost, soil amendment, or liquid or dry fertilizer. <br /> <br />Credit: Central Contra Costa Solid Waste Authority dba RecycleSmart <br />Composting uses different aerobic bacteria to digest the organics in the presence of oxygen, which does not <br />produce methane (but does release an amount of CO similar to that produced in AD). The digestion produces a <br />2 <br />solid compost, which can be used as a soil amendment or dry fertilizer. However, if the composted material is <br />wet (such as food waste), it needs considerable energy to power fan-blown air to constantly circulate through <br />5 <br />the compost pile or windrow to keep the anaerobic bacteria from digesting the food and releasing methane. <br />Soil amendments from organic waste streams in California represent a potential $200-400 million market in <br />6 <br />California, exceeding the likely value of energy products from the resource. <br />Both AD and composting can be done including wastes from humans and industry, such as sewage wastewater <br />7 <br />sludge, but in that case the resulting fertilizer may have contaminants including heavy metals, pharmaceuticals, <br />etc., which can make it unusable on food crops and reduce its profitability. So it is preferable to process food <br />waste and green waste separately from sludge to produce compost suitable for organic farming and gardening. <br /> <br />5 <br /> Production of large amounts of methane from a composting facility in the Bay Area was observed in 2020 by planes from the <br />Jet Propulsion Laboratory <br />6 <br /> CA Short-Lived Climate Reduction Strategy (2017) p. 31. <br />7 <br /> A recent study of composting examined its ability to break down 10 pharmaceutical and personal-care product residues in <br />biosolids collected from a wastewater treatment plant in San Diego. Fatih Büyüksönmez, of San Diego State University's <br />Department of Civil and Environmental Engineering, found that composting for 45 days reduced residues of 9 out of 10 <br />products by at least 85 percent. <br />Page 3 zero.waste.committee@california.sierraclub.org <br />