Laboratory Evaluation of Co-digesting Beef Manure and Waste Kitchen Oil

Abstract

Abstract. Co-digestion of beef cattle manure and waste kitchen oil (WKO) was conducted using semi-continuously loaded digesters under mesophilic conditions. Nine laboratory-scale anaerobic digesters were loaded every two days during the first 45 days, to test the effects of hydraulic retention time (HRT) of 14 (n=3), 17.5 (n=3) and 21 (n=3) days. After that the 21 days HRT was used to co-digest manure with 0% (n=1), 0.5% (n=2), 1.0% (n=2), 1.5% (n=2) and 2.0% (n=2) of WKO (Test 1) by volume. The control and oil additions corresponded to 1.46, 1.70, 1.93, 2.17 and 2.40 g-VS/L/day loading respectively. Variables evaluated included biogas production, methane concentration, pH, alkalinity, ammonia and microbial community. Total biogas and methane production per week increased linearly (p A second test was conducted using three treatments with greater replications: control (n=3), and 1.0% (n=3) and 2% (n=3) WKO levels. Biogas productions per week were 85.3% and 218%, while methane yields per week were 79.1% and 203% higher than the control, for the 1.0% and 2.0% WKO levels, respectively. Linear correlations were identified between oil addition level and many variables, including total biogas yield, methane yield and methane yield per VS destroyed. Metagenomics analysis indicated that bacteria were dominant with 97.8%, and archea represented 2.2% in the community. Populations of Clostridiales were 33.3%, 35.1% and 40.6%, while Bacteroidales were 31.5%, 28.8%, and 27.6% for the control, 1% and 2% WKO levels, respectively. Euryarchaeota Methanomicrobia YC-E6 was 1.5%, 1.3%, and 1.0%, but Euryarchaeota Methanomicrobia Methanomicrobiales was 0.4%, 0.7%, and 1.0% for the control, 1% and 2% WKO levels, respectively. Adding low amount of WKO as co-digestion feedstock can be a practical and effective biogas yield improvement method for the commercial beef manure AD plant.