Anaerobic Digestion of Petroleum Refinery Sludge: Effect of Pretreatment and Co-digestion

Abstract

Rapid industrialization in conjunction with urbanization is devouring natural resources worldwide and their processing or refining into useful products are leading to mounting global waste generation. Petroleum refinery sludge (PRS), an egregious solid residue generated from the effluent treatment plants (ETPs) of petrochemical refineries, poses an environmental hazard owing to its intricate hydrocarbon composition, necessitating competent treatment for secure disposal. The PRS generated from the biological treatment units of the ETPs has enormous potential for biogas production through anaerobic digestion. Selection of appropriate inoculum is crucial to foster a well-balanced environment with favourable microbial communities for initiating the anaerobic digestion process. In order to select an appropriate inoculum, the biodegradation of PRS was compared between undigested residue of animal manure, and anaerobically acclimated or digested sludge from an operational anaerobic reactor. Upon performing 1L batch anaerobic biodegradation assays, digested sludge provided a better seeding environment exhibiting maximum biogas yield with higher organic fraction removal resulting in improved biodegradability. 16S metagenome sequencing of digested sludge revealed significant predominance of Proteobacteria, Bacteroidetes and Firmicutes at phylum level possessing hydrocarbon-degrading properties.