Investigation of methane production by anaerobic co-digestion of food waste, fats, oil & grease, and thickened waste activated sludge using Automatic Methane Potential Test System

This project investigated the methane production by anaerobic digestion using Automatic Methane Potential Test System (AMPTS). Food waste (FW), waste cooking oil- Canola oil (FOG), and thickened waste activated sludge (TWAS) were used as substrates for anaerobic digestion in two sets of experiments. Energy harnessed from waste by anaerobic digestion can be used to replace fossil fuels, which release harmful compounds in the environment. Substrates and inoculum were characterized to find the content of total solids, total volatile solids, chemical oxygen demand, total organic carbon, and total nitrogen. All the substrates were digested individually in the first set of experiments. In the second set, they were combined in different proportions (four combinations) and were co-digested. All the experiments were carried at mesophilic temperature (37˚C). In this study, emphasis was given to the percentage of FOG which can be inhibitory for methane production. At the end of the first set, it was found that FW generated the maximum methane, followed by TWAS. Very less methane was produced from FOG. Results obtained from the first set established that FOG is not a suitable substrate for anaerobic digestion. From the second set of experiments, it was determined that FOG did not cause inhibition. However, presence of FOG in co-digestion process caused problems which led to decreased yield of methane in all the four combinations. These problems included accumulation of FOG at the top surface of the solution in AMPTS bottles, coating of oil on microbes’ bodies and substrates, lack of proper mixing in the bottles, and formation of a thick solution which included all the substrates, inoculum and bio-medium. As a result, in this study, co-digestion did not provide better methane yield than single substrate anaerobic digestion. It was determined by the second set’s results that FOG reduces the methane yield if co-digested with FW and TWAS