Enhanced biogas production potential of microalgae and swine wastewater using co-digestion and alkaline pretreatment.

Biogas yield obtained from anaerobic digestion of swine wastewater (SWW) needs to be increased to produce electrical energy. To enhance biogas and prevent pollution, use of mixed culture microalgae grown in wastewater (MWW) with SWW has attracted a lot of interest. This research was focused on the possibility of utilizing MWW. Six experiments using raw SWW and MWW, and their co-digestion were conducted on a laboratory scale in one-litre reactors with the ratio of inoculum and substrate of 70:30 under without and with alkaline pretreatment (using 3% NaOH for pH adjustment every 15 min at pH 11 for 3 h). The results showed that co-digestion had the major effect on increasing biogas and methane yields (0.735 and 0.326 m3/kg of volatile solids (VS) removed), and the highest chemical oxygen demand and VS removal (60.29% and 63.17%). For pretreatment, the effect of ammonia inhibition at a high pH of 11 had more influence on biodegradation than the effect of destruction of MWW's cell walls, resulting in a low biogas production of pretreated MWW and pretreated co-digestion. These findings affirm the potential of co-digestion, and the possibility of using both single and co-substrate MWW. Pretreatment could be improved at a lower alkaline pH condition. A pilot scale of co-digestion should be performed.