Oriented acidification of wasted activated sludge (WAS) focused on odd-carbon volatile fatty acid (VFA): Regulation strategy and microbial community dynamics

As the main intermediate metabolite in anaerobic digestion of wasted activated sludge (WAS), volatile fatty acids (VFAs) are proper substrate for mixed culture (MC) polyhydroxyalkanoate (PHA) synthesis. To further optimize the performance of MC PHA production process, VFA_{_odd} (i.e., VFA with odd carbon atoms) oriented acidification process was proposed and conducted in this study. Three regulation factors including reaction pH, fraction of added β-cyclodextrin (β-CD) and glycerol were selected and response surface methodology (RSM) was used to enhance and effectively regulate the VFA_{_odd} production while maintaining enough acidification degree in the WAS acidification. High percentage of VFA_{_odd} (larger than 60% and dominated by propionic acid) can be obtained in the operating condition area with glycerol addition ratio (quantified by C/N) ranging from 15 to 20 and reaction pH ranging from 8.0 to 9.5 when β-CD addition was held at zero level (0.2 g/gTSS) according to the RSM. Semi-continuous acidification and MC PHA production assays further verified the reliability and effectiveness of the VFA_{_odd} oriented acidification strategy. Microbial function group related to propionic acid production (G_prop) was defined based on the relationships between system function and microbial community structure, and 13 frequent species were found being involved in the G_prop. Roles of the group members in the oriented acidification were analyzed to understand the mechanisms of the regulation of VFA_{_odd} production at microbial ecological level. A synergistic effect of WAS and glycerol on the VFA_{_odd} production in the acidification process was revealed based on the ecological analysis.