OPTIMIZATION AND PERFORMANCE EVALUATION OF HOUSEHOLD ANAEROBIC DIGESTER
Abstract
Globally, one-third of food produced for human consumption is wasted. The waste stream of developing countries constitutes a substantial amount of food waste. In addition to contributing to greenhouse gas emissions, food waste is a significant source of leachate due to its high organic content and moisture content. While food wastes do not pose a threat to the environment in terms of pollution control, their disposal in landfills presents a serious concern for the environment. Food waste, which contains high levels of volatile solids and wettest portion of the waste stream, can be utilized as an energy source to offset the use of non-renewable energy.
The primary objective of this study is to design, operate and performance monitoring of household-scale anaerobic digester based on specific food waste composition for developing countries. There are many benefits of anaerobic digestion, including the cost effectiveness, faster methane production, and a smaller footprint. A laboratory scale study was conducted to investigate the impact of Food/Inoculum ratio and total solid (%) on food waste decomposition and gas production in anaerobic digester. To simulate the digester, laboratory scale reactors were filled with food waste. Cow manure and sludge were used as inoculum. Among the food waste reactors, the highest methane volume, as well as biogas volume, was generated by reactors with F/I=2 and total solid of 11%. Based on the results from the laboratory scale study, two sets (total 4) field scale anaerobic digesters (F/I=2 and 1.5) were installed at the Civil Engineering Laboratory Building in University of Texas, Arlington with food waste feedstock and were monitored for 180 days. Having successfully operated the first one, the second study included inoculum for the whole hydraulic retention period on Day 0, and two anaerobic digesters of F/I=2 were monitored for 120 days to determine the potential for lag phase reduction. The result from the anaerobic digester revealed that continuous flow of biogas can be achieved with average of 42 L/day for one-fifth size of the digesters. For the full-scale size, that will be of 210 liter per day which can be used for 1.25 hours of cooking daily for developing countries. The quality and amount of the biogas and quality of the leachate showed that the initial inclusion of inoculum for the whole hydraulic retention time on Day 0, and then operating the anaerobic digester with F/I ratio 2 decreased the lag phase from 100 days to 2 days and enhanced the food waste degradation in continuous anaerobic digester. Thus, it can be concluded that operating a household scale anaerobic digester is a sustainable food waste management system that results in enhanced methane and biogas production.