Converting food waste to biogas through aerobic and anaerobic digestion

Food waste (FW) is the largest waste stream going into landfills, but the least recycled. Typically, it can be a good substrate for anaerobic digestion due to its high organic content and high moisture. In this project, on-site aerobic bio-digester was considered as a pre-treatment method for efficient anaerobic digestion of FW materials for biogas production. The liquid effluent produced by on-site aerobic bio-digester was collected and used as the substrate material for anaerobic digestion. Previously, a detailed analysis of aerobic bio-digester technology, such as digester performance, residual material characteristics and potential value for energy recovery has not been evaluated. In this project, the chemical characteristics of liquid effluent were determined. The effluent had a pH level of 4.0 ± 0.2 and the temperature of 30°C. Its Dissolved Oxygen (DO) levels indicated the aerobic condition in the bio-digester. Also, the energy recovery potential of wastewater generated from different combination of food waste materials was tested. The results showed that wastewater from the bio-digester was an organic-rich material that could be readily biodegraded as it had a BOD5/TCOD (total COD) ratio of 0.72 on average. Liquid effluent generated from laboratory digestion of different food materials (e.g., vegetables, meats, flour products, etc.) were fed to laboratory scale anaerobic digesters to evaluate the biogas production potential. The results showed a good energy recovery. The average biogas production from different feed materials ranged from 29 to 102 mL/d/g TCOD. The lowest amount of biogas was produced from liquid digestate containing mostly vegetable waste. On the other hand, the highest biogas amount was observed with digestate from a mixture of food waste. Methane content in the biogas was consistently about 55%.