Biomethanation macrodynamics of vegetable residues pretreated by low-frequency microwave irradiation

The effects of microwave irradiation on the digestibility and biogas production of cauliflower (Brassica oleracea var. botrytis) and cabbage (Brassica oleracea var. capitata) leaves were investigated using biochemical methane potential (BMP) assays. Cow dung was utilised as inoculum. Different microwave powers (87.5, 175 and 350W) were applied in a first set of runs for 15min. The second set consisted of 20, 25 and 30min irradiation at 350W. Based on ANOVA analysis (α=0.05), biogas production was significantly higher for the irradiated substrates compared to controls. The peak biogas production was 700ml for 36days HRT for 350W/25min. Peak COD, SCOD, volatile and total solids removals were 54.84%, 39.08%, 34.60% and 71.96%, respectively. Phosphate and total nitrogen increased significantly. Cumulative biogas production data fitted the modified Gompertz equation well. The highest biogas yield was 0.271L/g VS_removed at a 350W microwave irradiation for 30min.