Effects of carbonaceous susceptors on microwave pretreatment of waste activated sludge and subsequent anaerobic digestion

Pretreatment of waste activated sludge is an accepted approach to improve the anaerobic digestion performance by accelerating hydrolysis. Recently, microwave irradiation has been gaining attention as a pretreatment method because it accomplishes remote, rapid, and targeted heating of sludge and assists the release of soluble organic constituents. This study demonstrates the effect of hyper-reactive dielectric carbon nanofiber additives on amplified microwave pretreatment and subsequent anaerobic digestion and compares to traditional activated carbons for the first time. Our findings show that when carbon nanofibers are used, microwave pretreatment increases the soluble chemical oxygen demand from 73 to 924 mg L⁻¹. This increase in sCOD corresponds to 25% improvement when compared to microwave pretreatment alone. Moreover, carbon nanofibers facilitate more biogas production (i.e., 24%) with higher methane content (i.e., 46%) when compared to no pretreatment. Our findings also provide engineering insights within a techno-economic framework for carbon nanomaterial-augmented microwave pretreatment.