| With the rapid development of economy in China, water body pollution bysulfate and nitrate containing organic wastewater has become more and more serious,which are crying out for solutions. Biological treatment of this wastewater has beenproved to be a promising strategy to achieve simultaneous removal of sulfate, nitrateand organic carbon. Furthermore, the elemental sulfur (S0) is obtained during theprocess as important by-product. A better understanding of the structure andfunction of functional microbial community structure is valuable since it could helpoptimize, diagnose and correct general problems of process.Targeting at thedisadvantage of process currently, GeoChip was employed in this study tocharacterize the microbial community of sulfate reduction&denitrifying sulfideremoval process (SR-DSR) and denitrifying sulfide removal process (DSR) toelucidate the mechanism of biological pollutant removal. Firstly, the performancesof two processes were assessed in this study, and key factors were analyzed forSR-DSR process to enhance S0conversion rate. Secondly, to improved element S0recovery, oxygen was induced into bioreactor. The effects of different concentrationof dissolved oxygen (DO) on reactor performance and microbial community wereanalyzed. Moreover, the mechanism of stimulation of S0conversion rate by DO wasrevealed with functional gene and species analysis. Lastly, the effects of operationaltrophic conditions were investigated to elucidate the important role of autotrophicand heterotrophic bacteria in sulfide oxidation and nitrate reduction process. Theresults provide more insights into structure, composition and potential activity ofmicrobial communities, and therefor can explain how to improve overallperformance and stability of process.The microbial community structure, diversity indices, and abundance offunctional genes were distinct between SR-DSR and DSR models. In contrast toDSR process, the abundance of sulfate-reducing bacteria (SRB) detected in SR-DSRprocess was higher, while some typical nitrate-reducing sulfide-oxidizing bacteria(NR-SOB), such as Thiobacillus denitrificans, Sulfurimonas denitrificans andParacoccus pantotrophus have lower abundant in SR-DSR model. This trend wassubstantially responded to the change of S0conversion rate in two models, whichpotentially suggests that these NR-SOB play important role in S0conversionprocess. Relatively low abundant of NR-SOB might be a major cause of low S0conversion rate in SR-DSR process. In the study, micro-aerobic situmulation was used to improve the S0conversionrate of SR-DSR process. The maximal S0conversion rate was increased to82.6%with DO=0.15mg/L when nitrate and oxgen were both electron acceptors. While themaximal S0conversion rate was increased to83%with DO=0.10mg/L when oxygenwas the sole electron acceptor. Dissolved oxygen has significant effect on thestructure of microbial communities and diversity indices. Functional gene analysisshown that abundance of denitrification genes were changed little, but the genesinvolved in sulfate reduction process were greatly decreased at DO0.35mg/L, whichindicated that SRB was inhibited at this concentration of DO. The abundance ofsulfur oxidation genes was increased under micro-aerobic situmulation. Underproper aeration rate conditions, the abundance of NR-SOB was increased with bothnitrate and oxygen as electron acceptors, while the diversity of SOB was detected alittle higher with oxygen as sole electron acceptor. The results suggested that S0conversion rate was enhanced by stimulating the activity of sulfur-oxidizingbacteria (SOB).The highest sustainable concentration of sulfide for autotrophic condition was400mg/L, while this load was up to800mg/L under the synergism of autotrophicand heterotrophic bacteria. The structure of microbial community was radicallydifferent between autotrophic and other trophic conditions. Low diversity indicesand abundance of denitrification genes were observed in autotrophic condition aswell as the decrease of nitrate removal efficiency, suggesting heterotrophicdenitrifiers play key role in DSR process. In addition, the reasons for drop of S0recovery were that autotrophic denitrifiers were strongly inhibited by highconcentration of sulfide during autotrophic desulfurization and denitrification stage,leading to performance deterioration. However, in autotrophic and heterotrophicdenitrifying sulfide removal stage, sulfide was removal by heterotrophic SOB andNR-SOB. Most importantly, acetate was added in influent wastewater in this stagewhich enhanced the performance of DSR process by NR-SOB enrichment culture.The functional communities and their interactive adjusts were disclosed in theprocess of simultaneous removal of sulfate, nitrate and organic carbon. In the study,a useful strategy was put forward to control a high-efficiency bioreactor with steadyperformance and functional community enrichment. It shows a great potential togive a direct on operation optimization of wastewater treatment in future. |
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