Calcium hypochlorite coupled with ultrasound pretreatment enhances methane production from sludge anaerobic digestion

For existing advantages in resource recovery and cost, anaerobic digestion (AD) is considered a proper technology to treat sludge. The insufficient efficiency of sludge AD however prevents its further application. This work reported a hybrid method by combining calcium hypochlorite (CH) with ultrasound (US) for sludge pretreatment to enhance the AD performance. Experimental data demonstrated that the optimal parameters of this co-treatment were CH at 0.08 g/g volatile suspended solids (VSS) coupled with US intensity of 1.0 W/mL, and relevant biomethane yield was 263.4 mL/g VSS, 15.2 %, 23.1 % and 56.6 % higher than individual CH, individual US and control, respectively. Simulation results showed that methane production potential and rate both increased under CH + US condition. Mechanism analysis indicated that abundant dissolved organic matters were generated through high-efficiency hydrolysis when sludge was treated with CH + US, because extracellular polymeric substances (EPS) and microbial cells were both sufficiently disrupted in treatment process. Gene analysis revealed that functional microbes were generally enriched by the co-treatment, and their total abundance markedly improved from 11.89 % to 24.87 % under CH + US condition.