Enhanced methane yield through sludge two-phase anaerobic digestion process with the addition of calcium hypochlorite

Abstract

This study investigated the effects of calcium hypochlorite (Ca(ClO)2) on biomethane generation from sludge two-phase anaerobic digestion system. In first (acidogenic) phase, volatile fatty acids (VFAs) were largely generated when pretreated by Ca(ClO)2, while the methane yield was severely inhibited. In second (methanogenic) phase, the methane yield was observably enhanced by Ca(ClO)2. Further calculation showed that the total methane yield from the two phases was firstly promoted from 156.0 ± 4.5 to 269.9 ± 5.2 mL when Ca(ClO)2 dosage enhanced from 0 to 1.6 g/L, which then reduced to 235.4 ± 5.5 mL when Ca(ClO)2 content reached 2.0 g/L. Mechanism analysis showed that the suppression of Ca(ClO)2 on coenzyme F420 activity was relieved in methanogenic phase, and the abundances of functional microbes in methanogenic phase were enriched when added with Ca(ClO)2. The Ca(ClO)2-based method well realized the balance between efficacy and economy, possessing outstanding potential for large-scale applications.