Anaerobic co-digestion technology is widely used for biogas generation from organic wastes. In this study, co-digestion of petroleum oily sludge (POS) for biogas production in bench-scale anaerobic digesters at thermophilic conditions was investigated. The effects of inoculum type on the biogas production were considered. Three types of inoculums were examined individually for the co-digestion of POS which were; poultry manure, cattle manure, and cow dung. The results revealed that the biogas production from poultry manure, cattle manure, and cow dung exceeded its production from uninoculated POS by 64.6, 20.94 and 6.1% respectively. Effect of C/N on the co-digestion process was also considered in this study. Modified Gompertz model was applied to describe the kinetic of the co-digestion process. The predicted and experimental results of biogas generation were fitted well with coefficients of determination > 0.96 indicating appropriate conditions of the co-digestion process. Statistical analysis was performed to estimate if there were significant differences in terms of cumulative biogas yield. A significance level value of < 0.05 was obtained.

This study investigates the potential of biogas recovery from used engine oil (UEO) by co-digestion with animals’ manure, including cow dung (CD), poultry manure (PM), and cattle manure (CM). The experimental work was carried out in anaerobic biodigesters at mesophilic conditions (37°C). Two groups of biodigesters were prepared. Each group consisted of 4 digesters. UEO was the main component in the first group of biodigesters with and without inoculum, whereby a mix of UEO and petroleum refinery oily sludge (ROS) was the component in the second group of biodigesters. The results revealed that for UEO-based biodigesters, maximum biogas production was 0.98, 1.23, 1.93, and 0 ml/g VS from UEO±CD, UEO±CM, UEO±PM, and UEO, respectively, whereby, for the UEO=ROS-based biodigesters, maximum biogas production was 3.49, 2.47, 3.64 and 2.44 ml/g VS from UEO+ROS±CD, UEO+ROS±CM, UEO+ROS±PM, and UEO+ROS, respectively. These results indicated that UEO was not feasible and efficient for biogas recovery since biogas production was very low in the first group of biodigesters compared to its recovery in the second group. A modified Gompertz model was applied to study the kinetics of the bio-digestion process. Measured and predicted values of biogas generation were fitted well with determination coefficients higher than 0.92.