Calcium Hypochlorite Promotes Dark Fermentative Hydrogen Production from Waste Activated Sludge

This study reported a high-efficiency and low-cost sludge pretreatment method using calcium hypochlorite [Ca(ClO)(2)] for promoting anaerobic fermentation performance. The experimental results indicated that the cumulative hydrogen yield was enhanced from 1.87 to 16.72 mL/g volatile suspended solids (VSSs) when the Ca(ClO)(2) dosage was increased from 0 to 1.5 g/L and then reduced to 13.80 mL/g VSSs when the Ca(ClO)(2) dosage reached 1.8 g/L. The mechanism study revealed that Ca(ClO)(2) efficiently disrupted sludge extracellular polymeric substances and microbial cells, producing more soluble organics for the subsequent biochemical processes. Beyond that, the biodegradability of sludge organics was promoted by Ca(ClO)(2) pretreatment. Biochemical reaction kinetic analysis indicated that the activities of microbes responsible for hydrogen consumption were severely inhibited when treated with Ca(ClO)(2). The two decomposition products of Ca(ClO)(2), Ca(OH)(2) and HClO, positively affected the hydrogen yield, with the contribution of Ca(OH)(2) being greater than HClO. Microbial community analysis illustrated that the fermentative microbes were markedly enriched by Ca(ClO)(2) pretreatment, with the abundances found to be 3.21 and 45.62% in control and Ca(ClO)(2)-pretreated fermenters, respectively. After fermentation, the Ca(ClO)(2)-pretreated sludge showed better dewaterability than the control, and the organic pollutants diclofenac and sulfamethazine, as well as the fecal coliforms, were largely removed by Ca(ClO)(2).

Automated summary

This study reported a high-efficiency and low-cost sludge pretreatment method using calcium hypochlorite for promoting anaerobic fermentation performance. The method effectively enhanced hydrogen yield and improved the biodegradability of sludge organics.