Developing a Robust Anaerobic Digestion Process for Co-Digestion of Food Waste and Municipal Solid Waste

Growing populations and energy demands require progress towards a circular economy wherewastes are transformed into resources. About 30 to 40% of the US food supply is wasted(USDA), mostly ending up in municipal landfills. This food waste can be used as a substrate inanaerobic co-digestion (AcD) to increase biogas production from reactors and reduce greenhousegas emissions from landfills. However, AcD of food waste requires process optimization. Thisproject aims to identify mixtures of food wastes that result in optimum methane production andunderstand how microbial communities respond to shifts in mixtures of food waste types.Initially, 21 reactors were loaded with various food wastes in a unique simplex centroid mixturedesign. Three reactors served as controls, and 18 were fed either cellulosic, proteinaceous, or fat-rich (lipid) waste. Once methane generation passed peak production, one reactor from eachcategory was destructively sampled for microbial community analysis. The remaining reactorswere fed a combination of 50% of their original food waste type and 50% of a new one. Again,once methane generation passed peak production, one reactor from each food waste combinationwas destructively sampled. The remaining reactors were fed an equal part mixture of the threefood waste types. The protein-based reactors exhibited a large reduction in peak production afterbeing introduced to either a lipid or carbohydrate substrate. Lipid-based reactors experienced adecrease in peak production rate but an increase in cumulative methane yield when introduced tocarbohydrate waste. Carbohydrate-based reactors increased cumulative yield when introduced toeither protein or lipid waste. These results highlight the importance of pre-existing communitiesin responding to shifts in waste type, suggesting that communities formed from the carbohydratesubstrate are more resilient to waste changes than the microbial communities formed from theother substrate types. The statistical analysis of the cumulative methane yields found the lipidand carbohydrate mixture to be the most optimal for methane production. Molecular microbialcommunity analyses of reactor samples to observe the shift in communities attributable tosubstrate shifts are ongoing. This study provides insight into microbial adaptation to substratechanges and informs the development of operational procedures to optimize the AcD of foodwaste.