Photosynthesis assisted anaerobic digestion of cattle manure leachate in a hybrid bioreactor: An integrated system for enhanced wastewater treatment and methane production

Abstract

Cattle manure leachate (CML) is an abundant biodegradable waste with very low C/N ratio which hinders its effective treatment through anaerobic digestion process. In this study, photosynthesis assisted anaerobic digestion (PAAD) was used as a novel approach to overcome the carbon deficiency of CML. For this purpose, a hybrid bioreactor consisted of an up-flow anaerobic sludge blanket (UASB) reactor and an up-flow anaerobic packed bed photo-bioreactor (UAPBP) was used as anaerobic digester for enhanced wastewater treatment and methane production. In fact, the UAPBP was used as carbon recovery system through bio-fixation of CO2 from biogas using purple photosynthetic bacteria. The hybrid system showed stable performance at HRT of 43.2h (1.8d). The obtained COD removal, highest methane content and methane yield were 88%, 82% and 0.3m3.kg−1CODremoved, respectively. The performance of the hybrid system was also evaluated at very short HRT of 27.1h (1.13d) where 77% COD removal, 70% methane content and 0.27m3.kg−1CODremoved methane yield were obtained. The novel integrated PAAD process is a promising technique to treat low C/N ratio waste sources where simultaneous CO2 capture and methane content enhancement can be achieved.