Calcium Hypochlorite Promotes Dark Fermentative Hydrogen Production from Waste Activated Sludge

Abstract

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.

Adding Granular Activated Carbon and Zerovalent Iron to the High-Solid Anaerobic Digestion System of the Organic Fraction of Municipal Solid Waste: Anaerobic Digestion Performance and Microbial Community Analysis

“…These microbes can utilize the OFMSW to generate VFAs and H 2 , especially easily biodegraded carbohydrates and proteins in the OFMSW. 35 The relative abundances of Firmicutes accounted for 56.3–68.4% of the total population, which is the highest of 68.4% in the R-(GAC + ZVI) group. Firmicutes play the role of maintaining system stability and are known for their acid-forming capabilities.…”

“…Firmicutes , Bacteroidotas , Spirochaetota , Proteobacteria , synergistota , and Cloacimonadotas were the dominant bacteria at the phylum levels (Figure (a)). These microbes can utilize the OFMSW to generate VFAs and H 2 , especially easily biodegraded carbohydrates and proteins in the OFMSW . The relative abundances of Firmicutes accounted for 56.3–68.4% of the total population, which is the highest of 68.4% in the R-(GAC + ZVI) group.…”