Influence of Food Waste Composition and Volumetric Water Dilution on Methane Generation Kinetics

Goen Ho; Jaya Nair; Xian Fang Lou
Food water composition and the amount of water addition are strong determinants of a digester’s performance. Hence, the objective of this paper is to study how variations in the majoring food groups and water additions can affect digester performance. The performance of carbohydrate, protein, lipid and cellulose rich mixed food wastes, subjected to five factors of volumetric dilution, were evaluated in a controlled laboratory scale set up at 38°C and 28°C. Substrate degradation was high for all assays with 86.6 – 100% and 87.1 – 98.0% reduction in VS and COD respectively. Maximum methane (CH4) yield varied between 362.7 (carbohydrate at 1:2 dilution) and 0.53 m3 CH4/kg VS (protein at 1:6 dilution) at 38°C and 0.32 (lipid at 1:2 dilution) and 0.52 m3 CH4/kg VS (protein at 1:6 dilution) at 28°C with the maximum rate of CH4 production varying between 0.015 (lipids at 1:2 dilution) and 0.053 m3 CH4/kg VS/day (protein at 1:6 dilution) at 38°C and between 0.006 m3 CH4/kg VS/day (lipids a 1:2 dilution) and 0.026 (protein at 1:6 dilution) m3 CH4/kg VS/day at 28°C. Lipid rich waste obtained the lowest yield while cellulose and protein showed interchangeably the highest yield. To successfully digest lipid rich waste a dilution no less than 1:4 was required to improve CH4 generation and to drastically reduce retention time. Both Bo and maximum rate of CH4 production increased as dilution factor and temperature increased while lag phase decreased. Results indicate that with sufficiently long retention time, food waste up to a dilution of 1:2 did not experience irreversible inhibition problems and achieved high substrate degradation although sufficient water additions can significantly improve a digester’s lag time and CH4 generation potential.
Food Waste; Anaerobic Digestion; Kinetic Study; Small Scale; Methane; Organic Loading Rate
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