Study On Enhancing SCFAs Production From Waste Activated Sludge Fermentation Stimulated By Persulfate Combined With Sulfate Reducing Bacteria

Anaerobic fermentation is the preferred and the most feasible way to achieve the stabilization,reduction and recycle of WAS.Short-chain volatile fatty acids(SCFAs),with the high market value added,can be produced from anaerobic fermentation,are the ideal easily degradable carbon source for many biological treaments and synthetic reactions.Aiming at the difficult problems of limited hydrolysis rate and the restricted syntrophic acetogenesis by hydrogen-accumulation and thermodynamics during anaerobic fermentation,a new fermentation system of combining persulfate(PDS)pretreatment and synergistic sulfate reduction bacteria(SRB)to enhance solubilization of WAS and interspecies hydrogen transfer was proposed in this study.Moreover,the feasibility of strengthening the SCFAs production of WAS fermentation was studied.The effects of four typical methods of activating PDS on the yield of sulfate rdicals in oxidation system was explored,as well as the performance of acid production process by excited PDS and SRB synergistic system.The high-throughput sequencing technology was used to analyze the diversity,difference and structural variation of the microbial community in PDS combined with SRB fermentation system,which may provide a theoretical and technical basis for the partical application of the new fermentation system in the WAS fermentation.The main findings are as follows:1.Various bacterial sources were used to accumulate various incomplete fatty acid oxidized SRB in the laboratory,and the sulfate reduction rates of the SRB cultured by propionic acid type(HPr-SRB),butyric acid type(HBu-SRB)and valeric acid type(HVa-SRB)were 48%,56%,38%,respectively;the substrate utilization efficiencies of conversion from C3~C5 fatty acid to acetic acid reached 37%,24% and 20%,respectively.The high-throughput results showed that there were significant differences in the community structure among the three functional bacteria,which had their own abilities to degrade different volatile acids.2.The new system of PDS pretreatment combined with SRB is feasible to promote SCFAs yield from anaerobic fermentation.The maximum SCFAs yield by PDS pretreatment was 350.7 mg COD/g VSS,which was further promoted with the participation of SRB(393.7 mg COD/g VSS),which was 5.15 folds than that obtained in Control.Simultaneously,coupling with PDS and SRB promoted the conversion from long chain SCFAs to acetic acid.During 72 h fermentation,acetic acid yield in the PDS+SRB system peaked at 156.8 mg of COD/g VSS,which was 5.97 times and 1.25 times that of the Control and the PDS.3.Different lysis efficiencies of WAS was obtained in various excited PDS,including ferrous iron(Ferrous),zero-valent iron(ZVI),heat(Heat)and ultraviolet(UV),and the lysis efficiencies were 48.4%,40.6%,52.2% and 50.3% respectively,which were 1.1%~12.7% higher than that of the non-activated group(39.5%).Heat activation was most effective for WAS disintegration,which greatly promoted the release of organic matter from intracell and extracell into liquid phase.4.The maximum yield of SCFAs in Ferrous,ZVI,Heat,UV activated PDS pretreatment combined with SRB fermentation systems were 460.9 mg COD/g VSS,367.0 mg COD/g VSS,531.9 mg COD/g VSS and 507.8 mg COD/g VSS,respectively,which were 1.17,0.93,1.35 and 1.29 times of that in the non-activated group;compared with the fermentation time(216 h)to reach the peak of SCFAs production in the non-activated group,the maximum acid production period of PDS activated groups were shortened at least 24 h earlier,which were 120 h,144 h,168 h and 120 h respectively.By analyzing the components of SCFAs in the synergistic PDS pretreatment and synergistic SRB fermentation system,the results showed that the yield of acetic acid in Heat_PDS+SRB system is the largest,in other words,Heat_PDS+SRB system is the most effective way to convert C3~C5 fatty acids to acetic acid.5.The microbial community of the fermentation systems was further analyzed by high throughput sequencing technology.Alpha diversity index results showed that PDS pretreatment reduced the diversity of microbial communities of sludge samples.In the PDS+SRB group,due to the addition of mixed bacteria(SRB)and the interaction between SRB and anaerobic fermentation bacteria,some functional fermenting bacteria were enriched,which promoted hydrolysis and acidification of WAS.6.By analyzing the microorganism samples at phylum,class and genus levels,the results showed that functional microoorganism are mainly concentrated on three common fermentation bacteria phyla of Bacteroidetes,Firmicutes and Proteobacteria.At the class level,PDS pretreatment promoted Bacteroidia,Clostridia and Gammaproteobacteria,which are related to SCFAs production.In the SRB participating system,the three classes were further enriched and accumulated.At the genus level,the dominant bacteria related to hydrolysis and fermentation in the PDS pretreatment system is mainly concentrated on Acinetobacter,Faecalibacterium,Clostridium sensu stricto,Oscillibacter and Macellibacteroides.In the SRB collaborative system,in addition to further enriching the characteristic genus in the PDS samples,other anaerobic fermentation bacteria are further promoted to form the dominant functional community,including Bacteroides,Klebsiella,Morganella,Desulfovibrio and Escherichia/Shigella.The enhancement of SCFAs production in the new fermentation system was explained from the aspect of the molecular biology.Based on the correlation analysis of environmental factors and sample microbial functional community,it can be concluded that combining PDS pretreatment and SRB may have a great impact on shiping microbial functional community infermentation system,and the shift of microbial community could further affect theacidification process during anaerobic fermentation.