Feasibility of membrane distillation brine assistant anaerobic fermentation for enhancing carbon migration and recovery from excess sludge: Two wastes into one resource

Abstract

The carbon recovery from excess sludge has received rising attentions. This study developed an innovative membrane distillation (MD) brine assistant anaerobic fermentation. The Na+, instead of other ions in MD brine, disrupted O-H stretching and N-H/C-N stretches of amide I in proteins for loosening protein structure and reducing hydrophilic functional groups, which triggered considerable sludge disintegration and microbial cell lysis with plicated floc surface structure and organic fragment stripping. Thereby, the carbon sources of 785.90 mg/L were released, among which the tyrosine-like protein and soluble microbial by-products were identified as the crucial dissolved organic matters relating to enhancing anaerobic fermentation. As such, the volatile fatty acids (VFAs) production was improved to 1689.65 mg COD/L (55.93 mg C/g VSS) through 4-day MD brine assistant anaerobic fermentation, which was mainly composed by acetic and propionic acids (58.96–84.16%), while the acetoxylation was also facilitated by MD brine. Correspondingly, the carbon source biodegradation towards micromolecule shift was promoted, considerable carbon release and recovery rates of 18.27% and 13.31% were achievable, respectively. The VFAs and proteins were dominant soluble carbon sources, while the pretty high C/N of 10.4 was achieved in fermentation liquid, demonstrating the bio-availability of recovered carbon sources. The economic and carbon-emission reduction benefits of 167.94–412.26 CNY and 0.0726 ton CO2 were obtained by carbon recovery from each ton excess sludge solid.