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 350 W) were applied in a first set of runs for 15 min. The second set consisted of 20, 25 and 30 min irradiation at 350 W. Based on ANOVA analysis (alpha = 0.05), biogas production was significantly higher for the irradiated substrates compared to controls. The peak biogas production was 700 ml for 36 days HRT for 350 W/25 min. 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 0.271 L/g VSremoved at a 350 W microwave irradiation for 30 min. (C) 2017 Elsevier Ltd. All rights reserved.