Synergetic Bioproduction of Short-Chain Fatty Acids from Waste Activated Sludge Intensified by the Combined Use of Potassium Ferrate and Biosurfactants

The synergetic effect and underlying mechanism of potassium ferrate（PF） with tea saponin（TS, a biosurfactant） in producing short chain fatty acids（SCFAs） from anaerobic fermentation of waste activated sludge（WAS） were explored in this work.Experimental results showed that 0.2 g PF（gTSS）-1（total suspended solid） combined with 0.02 g TS（gTSS）-1 could further improve SCFAs' production, and the maximum SCFAs content reached 2008.7 mg COD L-1, which is 1.2 and 4.5 times higher than those with PF and TS individually added, respectively, and 5.3 times higher than that of blank WAS on Day 12. In the model substrates experiments, the degradation rates of bovine serum albumin and dextran with combination of PF and TS were 41.3% ± 0.1% and 48.5% ±0.06%, respectively, on Day 3, which are lower than those in blank WAS（with degradation rates of 72.3% ± 0.5% and 90.3% ± 0.3%）.It was revealed that the oxidative effect of PF and the solubilization of TS caused more organic matters to be dissolved out from WAS, providing a large number of biodegradable substances for subsequent SCFAs production. While WAS pretreated with the combination of PF and TS, the relative abundances of Firmicutes increased from 6.4%（blank） to 38.6%, and that of Proteobacteria decreased from 41.8%（blank） to 21.8%. The combination of PF and TS promoted the hydrolysis process of WAS by enriching Firmicutes, and then increased acetic acid production by inhibiting Proteobacteria that consumed SCFAs. Meanwhile, at the genus level,acidogenesis bacteria（e.g., Proteiniclasticum and Petrimonas） were enriched whereas SCFAs consuming bacteria（e.g., Dokdonella）were inhibited.