Residential Anaerobic Digester: Recommendations for Food Waste to Methane

In an effort to prevent global food waste and create a renewable energy source, the goal of this project was to design a residential, batch-scale, anaerobic digester for the purpose of converting food scraps to methane to be used as biofuel. A senior design team at Mercer University designed and constructed an 18.9-L anaerobic digester that could be built by the average homeowner. The anaerobic digester was monitored over 5 weeks. Plant-based food scraps were blended with anaerobic sludge obtained from a local wastewater treatment facility at a 7:1 ratio to create the feedstock to the digester. An automated mixer was used for mixing the digester. The temperature was held at between 35–38°C using aquarium heaters and heating tape. The substrate within the digesters was monitored biweekly for changes in BOD, COD, and TVS. Gas production and composition was analyzed weekly using a GEM 2000 landfill gas analyzer. Methane production eventually ceased as the pH within the digester dropped below 6.8 creating an uninhabitable environment for methanogenic bacteria.