Improvement of methane production from waste activated sludge by on-site photocatalytic pretreatment in a photocatalytic anaerobic fermenter

•A photocatalytic anaerobic fermenter was developed for sludge treatment.•On-site photocatalysis in the fermenter improved the degradation of sludge.•On-site photocatalysis in the fermenter enhanced methane production from sludge.•Results provide useful reference on combining photocatalysis and anaerobic digestion.

This paper reports a new technology that using on-site TiO2-photocatalytic pretreatment in the anaerobic digestion of waste activated sludge (WAS) can enhance WAS degradation and methane production in a novel photocatalytic anaerobic fermenter. The fermenter consists of a photocatalytic unit and a digestion unit. The photocatalytic unit can constantly supply soluble organics and has less negative effect on the activity of methanogens at the optimal photocatalytic time of 4 h per day. After anaerobic digestion for 35 days, 1266.7 ml/l-sludge of methane, 67.4% of volatile solid (VS) reduction and 60.5% of total chemical oxygen demand (TCOD) removal were achieved in the photocatalytic anaerobic fermenter, compared with 923.2 ml/l-sludge of methane, 48.9% of VS reduction and 43.5% TCOD removal in the control fermenter. The results indicate that timely utilization of solubilized organics by methanogens could avoid further mineralization by TiO2-photocatalysis, which not only improves methane production but also enhances WAS degradation.