pH and hydraulic retention time regulation for anaerobic fermentation: Focus on volatile fatty acids production/distribution, microbial community succession and interactive correlation.

Enriching suitable fermentative products by optimizing operation conditions could effectively improve the efficiency of anaerobic digestion. In the present study, pH (5.0-6.0) and hydraulic retention time (HRT) (2 h-12 h) were regulated for volatile fatty acids (VFAs) production during glucose fermentation in acidogenic continuous stirred tank reactor (CSTR). Results showed that acetate and butyrate dominated during pH regulation. HRT reduction favored butyrate production and formate retainment. Maximum total VFAs production with highest acetate content was achieved at pH of 6.0 and HRT of 6 h. Microbial analysis revealed that Clostridium_sensu_stricto_1 was predominant butyrate producer during pH regulation, and Bacteroides was main contributor when HRT shorter than 6 h. In addition to acetyl-CoA pathway, acetate could also be produced via homoacetogenesis by Parabacteroides, UCG-004 and norank_f__Acidaminococcaceae. These results would give guidance for enhancing targeted VFAs products by optimizing operational parameters or bio-augmentation with specific bacteria.