Metal Oxides and Ultraviolet Light-based Photocatalytic Pretreatment of Biomass for Biogas Production and Lignin Oxidation

Lignocellulosics are abundant and readily available as the raw material for the production of biogas. However, the structure of this raw material needs to be modified to increase its digestibility during anaerobic fermentation. Various pretreatment methods that have been proposed in the past have been examined; however, the focus of the present study was to pretreat a wheat straw (WS) substrate using an advanced oxidation process (AOP) with a metal oxide photocatalyst combined with ultraviolet (UV) irradiation. Four different metal oxides were examined at 0, 1, 2, 3, and 4% dosages (w/w) coupled with UV irradiation for 0, 60, 120, and 180 min. Experimental results revealed that among all metal oxide catalysts examined, only the 4% CuO combined with 180 min UV irradiation caused the most lignin to be released from the WS. This resulted in the highest vanillic acid (VA) being produced (4.32 +/- 0.15 mg VA/g VS). This WS pretreatment also resulted in a biomethane potential (BMP) assay of 384 +/- 16 NmL CH4/g VS. The BMP assay results revealed a maximum 28% increase in biodegradability and a 57% increase in methane production. The use of either metal oxide catalysts or UV irradiation alone resulted in ineffective WS pretreatment.