Process Evolution of Dry Anaerobic Co-digestion of Cattle Manure with Kitchen Waste

H. L. Li, X. L. Guo, F. F. Cao and Y. Wang

Abstract
Knowledge of the effect of kitchen waste on dry anaerobic mesophilic digestion of cattle manure is important for understanding and controlling the anaerobic co-digestion process. In this study, laboratory scale (Volume = 5 L) performance was evaluated using six different ratios of cattle manure to kitchen waste: 1:0, 11:1, 9:1, 7:1, 5:1 and 3:1. The selected conditions were: 10 % inoculum, 20 % total solids, and 35 °C temperature, optimum in the mesophilic range. The six ratios showed an initial start-up phase in the range between 1 and 4 days, and the initial methane generation began within 2 days of operation. After 22 days, 14.98 % of Volatile Solid was removed for reactor 4 (R4) at the ratio of 7:1 of cattle manure to kitchen waste, and the reactor showed higher volumetric average daily biogas generated of 10.47 mL g–1 VS day–1 and 54.51 % methane content. The methane yield for R4 reached 0.1223 L CH4 g–1 VS, followed by the other two ratios (11:1 and 5:1) with the value of 0.1213 and 0.1208 L CH4 g–1 VS, respectively. And the methane yield of cattle manure with no kitchen waste was 0.1033 L CH4 g–1 VS during 22 days of operation. The result indicated that kitchen waste could improve the digestion process for methane production provided that the total solid ratio of cattle manure to kitchen waste was no less than 5.

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Keywords
Cattle manure, kitchen waste, dry anaerobic digestion, methane