Effect Of Exogenous Signal Molecules Cooperating With Denitrifying Bacteria On Denitrification Of Activated Sludge System

With the improvement of people’s living standards,the composition of pollutants in domestic sewage is becoming more complex,and the eutrophication of water body caused by excessive nitrogen content is becoming more and more serious.Due to the influence of external interference,the traditional biological treatment is not effective in removing nitrogen elements or the system operation cannot guarantee long-term stability.Among the methods to solve such problems,the biological enhancement technology has highlighted a good advantage,and the addition of bacteria to enhance the performance of biochemical treatment is an important method.There is no systematic conclusion on the precise regulation of signal molecules and the influence of threshold changes on biological systems.Therefore,in this study,exogenous signal molecules were used to study the regulatory role of exogenous signal molecules in enhancing the nitrogen removal performance of SBR by bacterial strain culture and SBR.It is elaborated from the following three aspects:（1）Static tests were carried out on the effect of exogenous signal molecules on the performance of FX-4 denitrifying bacteria.The signal molecules C6-HSL and C12-HSL of exogenous AHLs（acyl-homoserine lactones）were added into the denitrification resieve medium to explore the effect of AHLs on the removal of NO₃^--N from FX-4.The results showed that both C6-HSL and C12-HSL could effectively improve the NO₃^--N removal performance of FX-4 and increase the biomass of FX-4.Compared with C6-HSL-denitrifying bacteria treatment group,the NO₃^--N removal effect of C12-HSL-denitrifying bacteria treatment group was the best.The C12-HSL of 50 nmol?L^-1can greatly improve the NO₃^--N removal effect of FX-4.（2）The dynamic test of the effect of exogenous signal molecules on the nitrogen removal performance of SBR system was carried out.Based on conclusion（1）,C12-HSL and FX-4 denitrifiers of 0,5,50,100,200 and 500 nmol?L^-1were combined into six treatment groups and added to the SBR activated sludge system,respectively.The effects of different proportions of C12-HSL-denitrifying bacteria on denitrification performance and signal molecule concentration of SBR activated sludge reaction system were investigated.The results showed that the addition of 100nmol?L^-1C12-HSL-denitrification bacteria had the most significant positive effect on the removal performance of TN in the SBR reactor,and the NO₃^--N effluent concentration in the 100 Nmol?L^-1C12-HSL-denitrification bacteria treatment group was about 45 mg?L^-1lower than that in the control group.（3）The experiment analyzed the link in which the signal molecule can show the best strengthening effect.FX-4 denitrifying bacteria and C12-HSL signal molecules were added to the SBR reactor by different dosing methods.The effects of conventional denitrification indexes,types and concentrations of signal molecules,microbial community structure diversity and denitrification functional genes in the reactor on denitrification performance of the sludge system were analyzed.The results showed that:The application of additional signal molecules-denitrification bacteria can effectively improve the nitrogen removal performance of the SBR system.Among them,the effect of W₃group using the common addition strategy is more significant,and the nitrogen removal effect is better.The detection results of signal molecule types and concentration changes showed that the addition of C12-HSL signal molecule and denitrifying bacteria together could enrich the types and contents of signal molecules in the system,indicating that this addition strategy could promote the microbial secretion of a large number of endogenous signal molecules in the activated sludge of SBR reactor,induce quorum sensing,and thus significantly improve the nitrogen removal performance.Microbial community analysis results showed that adding C12-HSL signal molecule-denitrifying bacteria could significantly affect the microbial community structure in activated sludge,increase the proportion of nitrification and denitrifying related bacteria,change the microbial community structure in activated sludge system,and promote microbial population succession.The test results of functional genes for denitrification showed that adding C12-HSL signal molecule-denitrifying bacteria changed the original denitrification process of activated sludge which was jointly completed by aerobic denitrification and anoxic denitrification.The traditional anoxic denitrification was mainly applied to strains and signal molecules separately,while the main denitrification mode of strains and signal molecules was changed to aerobic denitrification process.In this study,the nitrogen removal performance of the SBR reactor was enhanced by the synergistic effect of signaling molecules and denitrifying strains,and the addition of signaling molecules was used to induce quorum sensing to improve the water quality of domestic sewage plants,and provided a theoretical basis for subsequent practical applications.