Optimizing waste-to-energy conversion: the impact of catalytic pretreatment on thermophilic anaerobic digestion of sewage sludge

Abstract

Untreated sewage sludge from wastewater treatment plants poses a significant ecological and public health risk. Anaerobic digestion of activated sewage sludge offers a sustainable method for energy recovery, though the low biodegradability of sludge limits methane production. This study investigates the impact of catalytic pretreatment using copper sulfate (CuSO₄), biochar, and sodium hydroxide (NaOH) on methane yield in thermophilic anaerobic digestion (55–60 °C). Batch experiments demonstrated that biochar (4 mm (2% w/v)) pretreatment achieved the highest total biogas volume (6502.2 mL) and biochemical methane potential (BMP: 866.88 mL CH₄ per g VS), with a methane content of 47.96%, by facilitating microbial syntrophy and direct interspecies electron transfer (DIET). NaOH (0.02 M, 24 h) enhanced hydrolysis, leading to elevated volatile fatty acids (VFA: up to 2000 mg L⁻¹) and a VFA/TIC ratio of 0.89, necessitating pH stabilization. CuSO₄ (1% w/v, 48 h) treatments improved methane content (47.44%) but increased hydrogen sulfide levels (up to 0.84%), requiring desulfurization. Statistical analyses (ANOVA, PCA) confirmed that catalytic pretreatments significantly enhanced biogas yield (p < 0.001). These findings support the use of catalytic pretreatment as a scalable strategy for optimizing waste-to-energy conversion, aligning with SDG 6 (clean water and sanitation), SDG 7 (affordable and clean energy), and SDG 13 (climate action). The findings highlight how anaerobic digestion can be optimized through catalytic pretreatment, providing insights into scalable and affordable methods for waste-to-energy applications.