Secondary acidogenic fermentation of waste activated sludge via voltage supplementation: Insights from sludge structure and enzymes activity

Microbial electrolysis cells were integrated with the anaerobic digestion at different fermentation stage (0th day and 30th day) to explore the bio-electrochemical enhancement of acidogenic fermentation from waste activated sludge. Results showed that significant increases in volatile fatty acid production can be achieved by electrically-assisted acidogenic fermentation (0th day to 12th day). In comparison, volatile fatty add production during secondary acidogenic fermentation (30th day to 42nd day) via voltage supplementation was also investigated. The concentrations of soluble total organic carbon, soluble protein, soluble polysaccharide via voltage supplementation during the secondary acidogenic fermentation process were improved from 69.9, 50.3, and 18.8 mg/L to 260.6, 135.6, and 43.8 mg/L, respectively. Meanwhile, fractal dimension (D-f) value was decreased via voltage supplementation along with the significantly improving of protease and alpha-glucosidase activities. These results suggest that the presence of voltage brought a secondary solubilization and hydrolysis of sludge via loosening sludge structure and promoting corresponding enzymes activities, thus improved the secondary acidogenic fermentation performance of sludge. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Microbial electrolysis cells integrated with anaerobic digestion showed significant enhancement of acidogenic fermentation from waste activated sludge. Electrically-assisted acidogenic fermentation and voltage supplementation resulted in increased production of volatile fatty acids. Voltage supplementation also led to improvements in soluble organic carbon, protein, and polysaccharide concentrations, as well as enzymatic activities, suggesting a secondary solubilization and hydrolysis of sludge.