Enhancing Methane Production from Dewatered Waste Activated Sludge through Alkaline and Photocatalytic Pretreatment

Abstract

Massive amount of waste activated sludge generated from wastewater treatment plants makes an abundant source of biomass. Effective utilization of this bioresource through anaerobic digestion requires prior disintegration of sludge matrix to increase the availability of organic matter, which needs pretreatment. This study investigates the effect of alkaline, photocatalytic, and combined pretreatment on disintegration and methane production of dewatered waste activated sludge. Different concentrations of NaOH (0.2, 0.4, 0.6 & 0.8%) and TiO2 nanoparticle (0.3, 0.4, 0.5 & 0.6 g/L) solutions were used to soak the dewatered waste activated sludge for evaluating the effect of alkaline, photocatalytic, and combined pretreatment on the disintegration and biogas production. Results show that individual pretreatment resulted in maximum disintegration degree of 11.3% and 5.2% at 0.8% NaOH and 0.6 gTiO2/L, respectively. Whereas combined pretreatment of 0.8% NaOH – 0.4 g/L TiO2 yielded 37% DDsCOD of dewatered waste activated sludge. Anaerobic digestion results show that 0.4% NaOH and 0.5 g/L TiO2 pretreated dewatered waste activated sludge yielded maximum methane, which was 50.4 and 32.6% enhanced as compared to control. Similarly, alkaline-photocatalytic (combined) pretreatment of dewatered waste activated sludge at 0.4% NaOH and 0.5 g/L TiO2 resulted in maximum methane yield of 462 NmL/gVS, which was 71.1% higher than that of control. Modified Gompertz model fitted the cumulative methane yield data well for pretreated and untreated sludge.