Enhancing methane production from dewatered waste activated sludge through alkaline and photocatalytic pretreatment.

Waste activated sludge generated from wastewater treatment plants makes an abundant source of biomass. Its effective utilization through anaerobic digestion (AD) requires pretreatment to disintegrate the sludge matrix and increase organic matter availability. In this study, dewatered waste activated sludge (DWAS) was subjected to alkaline, photocatalytic, and alkaline-photocatalytic pretreatment for its disintegration and subsequent methane production using different concentrations of sodium hydroxide and titania nanoparticles. Individual pretreatment resulted in maximum disintegration degree (DDsCOD) of 11.3 and 5.2% at 0.8% NaOH and 0.6 gTiO2/L, respectively. Alkaline-photocatalytic pretreatment yielded 37% DDsCOD at 0.8% NaOH-0.4 g/L TiO2. As compared to control, AD at 0.4% NaOH and 0.5 g/L TiO2 pretreatments yielded maximum methane, which was 50.4 and 32.6% higher. Similarly, alkaline-photocatalytic pretreatment at 0.4% NaOH-0.5 g/L TiO2 yielded methane as 462 N mL/g VS, which was 71.1% higher. Modified Gompertz model fitted the methane yield data well.

Effect of alkaline and alkaline-photocatalytic pretreatment on characteristics and biogas production of rice straw.

To overcome recalcitrant nature and investigate enhancement of biogas production of rice straw (RS), it was subjected to pretreatment under mild conditions. Alkaline pretreatment using sodium hydroxide (NaOH), photocatalytic pretreatment utilizing titania nanoparticles (TiO2 NPs) and alkaline-photocatalytic pretreatment was used to disrupt the lignocellulose complex. As compared to raw RS, maximum biogas and methane enhancement due to alkaline pretreatment was observed for 1.5% w/v NaOH pretreated RS which was 50 and 71% respectively. Photocatalytic pretreatment of RS at 0.25 g/L TiO2 increased biogas and methane yield by 30 and 36% respectively. However, maximum biogas and methane enhancement was observed for alkaline-photocatalytic pretreatment at 1.5% w/v NaOH-0.25 g/L TiO2 which was 74 and 122% respectively. Comparatively high enhancements were observed during alkaline-photocatalytic combined pretreatment due to increased cellulose and decreased lignin content. Moreover, the experimental data obtained from the experiments were validated using a non-linear kinetic model.