Feasibility of home biogas generation from food waste

The purpose of this study was to investigate the production of useful biogas (methane) and system stability of anaerobic digesters for use in residential homes. Economic analysis and theoretical methane yield calculations were used to determine a hydraulic retention time (HRT) and volatile solids (VS) loading rate of 16 days and 4 g/L-day, respectively, for two 9L plug flow reactors using kitchen waste from a North campus dining hall. Although operating the reactors at these conditions led to high biogas production (greater than 15L/day), volatile fatty acid (VFA) accumulation after only one HRT rose to levels unfavorable to methanogens. The reactors were allowed to return to safe VFA levels by halting VS loading, and then more conservative conditions were used. An HRT of 27 days and a loading rate of 2.5g VS/L-day led to steady biogas production of 12L/day, but again led to high VFA levels and visible fat and oil accumulation after slightly more than one HRT. New substrate was obtained, and meats, fats, and oils were separated before being blended and fed at the same 27-day HRT and 2.5 g VS/L-day loading rate. This led to average biogas production just over 10L/day, and decreasing VFA concentrations after an initial spike at the start of the feeding period. It is possible this was due to the addition of trace metal solution to the feedstock, or may have been the result of a reasonable feeding rate that properly enriched for methanogens.