Integrated anaerobic digestion and photodegradation of slaughterhouse wastewater: Energy analysis and degradation of aromatic compounds

Combined anaerobic digestion (AD) and photodegradation of slaughterhouse wastewater (SWW) was carried out to remove biodegradable chemical oxygen demand (COD) and biorecalcitrant aromatic compounds which were mainly p-cresol and dibutyl phthalate (DBP). The synergy between the two processes was analyzed through biodegradability enhancement by photodegradation and supply of bioenergy through AD to supplement the energy requirement of the photodegradation process. Degradation products of each process were determined using gas chromatography coupled with a mass spectrometer (GC–MS). Anaerobic digestion as a stand-alone process removed up to 80% COD, while it could only remove about 35% of the aromatic compounds. Photodegradation, as a post-treatment to the AD, removed 92% of the aromatic compounds and enhanced the biodegradability of the digester effluent by 50%, which could be recycled to the AD unit. The aromatic compounds were photodegraded via phthalic acid and hydroquinone. Also, AD as an initial step removed fats, oils, and grease which otherwise would have hindered catalytic activity during photodegradation post-treatment. The biomethane produced could supplement up to 20% of the electricity requirement by the energy-intensive photodegradation process to achieve total pollutants removal, making the integrated process to be a viable option for SWW management.