Anaerobic Digestion and Energy Recovery from Food Waste

摘要

This treatability study evaluated the technical and start-up considerations of biogas productionand energy recovery from digestion of food wastes in the absence of waste activated sludge (i.e.,separate food waste digestion rather than co-digestion), aiming to support design of full-scaleanaerobic digesters at Department of Defense (DOD) installations. Project objectives includedcharacterizing the composition and variability of multiple food wastes from Mitchell Hall at theU.S. Air Force Academy (USAFA), quantifying food waste digestibility and energy yield,identifying potential nutrient limitations, and determining appropriate specific energy loadingrates (SELR) for these wastes. The SELR is a measure of energy loading relative to the reactorbiomass, and is an innovative approach to characterizing digester capacity and stability. Thetreatability study consisted of three phases. In Phase I, food waste was collected from 15different meals at USAFA’s Mitchell Hall, as well as a sample of material from the grease trap.These 16 samples were analyzed for moisture, protein, fat, ash, and carbohydrate content, as wellas for volatile solids (VS), chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), andtotal phosphorus. Selected samples were also analyzed for trace metals. Phase II was a test of thebiological methane potential (BMP) of each of the 16 wastes. The characteristics of the food andgrease trap wastes were examined for correlations with the BMPs of the wastes. In Phase III,food wastes were digested in bench-scale, semi-continuous reactors and monitored using anonline respirometer capable of continuously monitoring gas flow rate and gas composition. Thedigesters were operated under varying conditions including composition (e.g., food waste withand without grease trap waste), SRTs between 10 and 100 days, organic loading rates between 2and 10 g COD/L/day, feed VS ranging from 4 to 15 percent, and with nutrient addition. Theresults of the bench-scale analyses were used to calibrate a preliminary economic and digestionmodel, and to guide the design of the pilot system. Pilot testing will be conducted in 2012.