Study On Properties And Mechanism Of Simultaneous Nitrification,Denitrification And Phosphorus Removal Via Sulfur-autotrophic Denitrification Combine With BAF System

The excessive discharge of secondary effluent into aquatic environments is a main cause of eutrophication.This seriously restricts the development of social economy and endangers the health of human beings.Thus,China has established more stringent surface water discharge standards?TN<2 mg/L,TP<0.2 mg/L,GB3838-2002?to control the occurrence of eutrophication.To efficiently remove the nitrogen and phosphorus pollutants from the secondary effluent,the sulfur autotrophic process combined with BAF system was established in this study.Though change of fillers properties,filling mode,DO concentration and HRT to achieve NH₄⁺-N,NO₃^--N and PO₄^3--P simultaneous and efficient removal.And then the regulate mechanism of sulfur autotrophic process was deeply explored via Fe²⁺-mediated,EPS secretion and interspecific communication.?1?When the DO=1.2-1.5 mg/L and the HRT=8-12 h?Phase IX?,R3 and R4 with sulfur and pyrite as composite fillers achieved the NH₄⁺-N,NO₃^--N and PO₄^3--P simultaneous and efficient removed,corresponding TN and PO₄^3--P effluent concentrations were maintained within 2 mg/L and 0.2 mg/L,respectively.The SSA and PD of pyrite were increased by calcining,which was beneficial microbial enrichment and the nitrogen and phosphorus removal performance improvement?R5?.And then the R7 with calcined pyrite combined with the sulfur as composite fillers achieved the NH₄⁺-N,NO₃^--N and PO₄^3--P simultaneous and efficient removed under the DO=1.2-2.5 mg/L and the HRT=6-12 h,and the application scope of sulfur autotrophic process was expanded.Meanwhile,the R7 also decreased the H⁺and SO₄^2-yield,corresponding effluent pH value and SO₄^2-concentration below the 6 and250 mg/L national emission limits,respectively.?2?In order to deeply discuss the effect of the electron donor,DO concentration and HRT changes on the nitrogen and phosphorus removal performance via sulfur autotrophic process,the TN and PO₄^3--P removal kinetic models were fitted.The reaction order?First-order?of the SAD process?R1?was higher than that of the PAD process?Zero-order?,which indicated that the providing electron capability of sulfur as filler was significantly stronger than pyrite.While the TN removal process in R5with calcined pyrite as filler was best fitted by Half-order kinetic model,which was improved the providing electron capability of pyrite.In addition,the nitrogen and phosphorus removal process of R7 with sulfur combined with calcined pyrite as composite fillers was best fitted by the First-order kinetic model;the providing electron capability was further enhanced.Moreover,the PO₄^3--P removal process in R7 was best fitted by the First-order kinetic model,the reactor order was higher than that the R2-R6.When the DO concentration and HRT were controlled at the 1.2-1.5mg/L and 8 h,the nitrogen and phosphorus removal reaction rate constant of R7 was the largest,the nitrogen and phosphorus removal efficiency was the highest.?3?Fe²⁺,EPS and signal moleculars production are closely related to the nitrogen and phosphorus removal performance.Meanwhile,the Fe²⁺,EPS and signal moleculars through regulating mediating the electron transfer system,biofilm properties and interspecific communication processes also was the key to pollutant removal.Among them,Fe²⁺could improve the ETSA of the reaction process and reduce the EIS,which accelerated the electron transfer efficiency and enhanced nitrogen removal performance.Meanwhile,the Fe²⁺also could stimulate bacteria to secrete more EPS and signaling molecules.The EPS production was not only contribute to biofilm formation and structural stability,but also accelerated electron transport efficiency;the pollutant removal performance was also improved.Furthermore,the production of signal molecules help to the AHL-QS regulation improvement,it could regulate the density of bacteria and indirectly affect the pollutants removal.Therefore,Fe²⁺-mediated,EPS production and interspecific communication processes were interact and promote each other,which was important regulation mechanism of sulfur autotrophic denitrification process.Bacterial community changes indicated that the Ferritrophicum,Thiobacillus,Simplicispira,Nitrosomonas,Nitrospira etc as major genera were enriched simultaneously at DO concentrations of 1.2-1.5 mg/L and HRT of 8 h?Phase IX?.Meanwhile,the C₆-HSL,C₈-HSL,C₁₀-HSL and C₁₂-HSL yield via nitrifiers autotrophic denitrifiers were obviously increased,which enhanced the AHL-QS system and accelerated the simultaneous enrichment of nitrifiers and autotrophic denitrifiers,this is also important guarantee for simultaneous removal of NH₄⁺-N and NO₃^--N.In summary,the sulfur autotrophic process combined with the BAF system realized NH₄⁺-N,NO₃^--N and PO₄^3--P simultaneously and efficiently via change of fillers properties,filling mode,DO concentration and HRT.Moreover,the theoretical mechanism of sulfur autotrophic denitrification process was discussed in detail through the Fe²⁺-mediated,EPS production and AHL-QS regulatory mechanisms,which provides an alternative method to further treatment secondary effluent.