How dose calcium hypochlorite promote the methane production from sludge anaerobic digestion: A mechanism study from enhanced biodegradability of recalcitrant substances

The application of calcium hypochlorite (CH) in waste activated sludge (WAS) treatment for enhancing the anaerobic digestion performance has been widely investigated in recent years. However, the underlying mechanisms for CH affecting the biomethane yield during sludge anaerobic digestion are still largely unknown. This work explored the impacts of CH with different contents on anaerobic methane generation from sludge, as well as the relevant mechanisms. Experimental results showed that the biomethane production firstly increased from 164.8 ± 4.2 to 220.5 ± 6.2 mL/g VSS (volatile suspended solids) with CH content raised from 0 to 1.0 g/L, which then started to decrease with further increased CH content. Mechanism analysis demonstrated that CH efficiently disintegrated sludge flocs, producing more biodegradable organics for anaerobic digestion. Beyond that, the biodegradability of recalcitrant humus and lignocellulose substances was enhanced by CH treatment, as higher methane yields were attained from CH treated model substrates when compared with the control. Microbial community analysis indicated that most of the functional microbes were enriched after CH treatment, with the total abundance detected to be 17.72 % and 25.20 % in control and CH pretreated reactors, respectively. Economic calculations demonstrated that the benefit of the CH-based method efficaciously covered the cost, indicating that the balance between economy and technology was achieved.