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

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 43.2 h (1.8 d). The obtained COD removal, highest methane content and methane yield were 88%, 82% and 0.3 m3.kg−1 CODremoved, respectively. The performance of the hybrid system was also evaluated at very short HRT of 27.1 h (1.13 d) where 77% COD removal, 70% methane content and 0.27 m3.kg−1 CODremoved 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.