Improving volatile fatty acid yield from sludge anaerobic fermentation through self-forming dynamic membrane separation

[Display omitted] •VFA yield from sludge anaerobic fermentation is improved by SDM separation.•Stable SDM operation is maintained in separating high-TSS fermentation sludge.•Timely substrates retention and product discharge are achieved by SDM separation.•Enzymatic activities in fermentation sludge are enhanced by SDM separation.•Functional bacteria are enriched by SDM separation. Self-forming dynamic membrane (SFDM) separation was applied to the conventional sludge fermenter for improving VFA yields. Results indicated SFDM presented good performance in transferring products, retaining substrates, and enriching useful bacteria. The retention ratios of suspended solids, soluble COD, proteins, and polysaccharides reached 99%, 30%, 70%, and 40%, respectively, and more than 90% of the VFAs and ammonia could be transferred in a timely manner. The structure of the microbial community was optimized, which led to enhanced releases of hydrolytic enzymes and accelerated enrichments of functional bacteria. Protease and β-glucosidase activities increased from 1.0 to 5.0U/mL and 15.0 to 23.0μmol/L·h, respectively. VFA yield and sludge conversion ratio increased by 233.3% and 227.9%, respectively. Moreover, SFDM had good operation stability, including a short formation time, a long operation period, and a low transmembrane pressure. These results show VFA yield from sludge fermentation can be greatly improved by SFDM separation.