Synergistic increase of bio-hydrogen production from sludge anaerobic fermentation by thermal hydrolysis coupled with calcium hypochlorite pretreatment

To solve the problem of low bio-hydrogen yield from anaerobic fermentation (AF) of sludge, a novel and efficient method by combining thermal hydrolysis (TH) with calcium hypochlorite (CH) for sludge pretreatment was proposed in this study. Experimental data demonstrated that TH + CH method synergistically promoted the bio-hydrogen production from sludge. The optimal condition of the combined pretreatment was TH at 70 °C plus 0.12 g/g volatile suspended solids (VSS) of CH, and relevant hydrogen yield was 22.52 mL/g VSS. Mechanism study exposed that TH + CH method effectively destructed extracellular polymeric substances (EPS) and sludge cells, causing the promotion of hydrolysis rate and generation of abundant fermentation substrates. In the several biochemical processes of sludge AF, acidogenesis and acetogenesis that responsible for hydrogen generation were not or only slightly suppressed by TH + CH pretreatment, while homoacetogenesis, sulfate-reducing and hydrogenotrophic methanogenesis that can consume hydrogen were severely inhibited under this condition, resulting in hydrogen accumulation. Microbiological analysis demonstrated that the functional bacteria (e.g. Rhodobacter , Proteiniborus and Petrimonas ) related to hydrogen generation were all enriched under TH + CH condition.