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

Huang, Long, Chen, Zhiqiang, Xiong, Dandan, Wen, Qinxue, Ji, Ye
Water research 2018 v.142 pp. 256-266
acidification, activated sludge, anaerobic digestion, beta-cyclodextrin, carbon, community structure, glycerol, metabolites, microbial communities, mixed culture, pH, polyhydroxyalkanoates, propionic acid, response surface methodology, synergism, volatile fatty acids
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 (Gprop) was defined based on the relationships between system function and microbial community structure, and 13 frequent species were found being involved in the Gprop. 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.