Study On The Characteristics And Mechanism Of Simultaneous Removal Of Nitrate And Cd(?) By The Manganese-oxidizing Denitrifying Bacterium

In this study,two strains(H-117(Pseudomonas)and SZ-28(Achromobacter))with high efficient nitrate removal characteristics had been investigated the removal capacity of cadmium(Cd(?)),the remove Cd(?)mechanism,the nitrogen removal ability,the characteristics of denitrification products and the effects of various environmental factors on the removal of heavy metals and denitrification.And the removal characteristics of Cd(?)and nitrate in mixotrophic bioreactor.Suggesting that:(1)In the mixotrophic condition,the Box-Behnken design was performed with three factors:Mn(?)concentration(10,40,70mg·L^-1);Cd(?)concentration(10,30,50mg·L^-1)and temperature(20,30,40?).According to response surface methodology(RSM)analysis,the maximum Cd(?)removal efficiency of 85.67%was obtained under the optimum conditions:temperature of 30.48?,Mn(?)concentration of 52.13mg·L^-1and Cd(?)concentration of 12.78mg·L^-1.The mechanism of Cd(?)removal was investigated,the results indicated that MnO₂adsorption and p H value increase were the main contributor to remove Cd(?).Moreover,meteorological chromatography analysis indicated that the characteristics of gas composition could be influenced by Cd(?).Results shown that nitrogen is the end product of denitrification,and Cd(?)can inhibit the release of nitrogen and increase the production of nitrous oxide.Sequence amplification identified the presence of the MCO(multicopper oxidase)gene in strain H117,indicating that the strain has the capacity to oxidize the Mn(?).XRD and SEM analysis confirmed that the oxide of Mn(?)was MnO₂.(2)Zero-valent iron(ZVI),nanoscale zero-valent iron(n ZVI),Fe(?)and Mn(?)were investigated for their effects on mixotrophic denitrification coupled with cadmium(Cd(?))adsorption process by Acinetobacter sp.SZ28.The removal rates of nitrate were 0.228mg·L^-1·h^-1(ZVI),0.133mg·L^-1·h^-1(n ZVI),0.309mg·L^-1·h^-1(Fe(?))and0.234mg·L^-1·h^-1(Mn(?)),respectively.The Cd(?)removal efficiencies were 97.23%(ZVI),95.79%(n ZVI),80.63%(Fe(?))and 84.58%(Mn(?)),respectively.Meteorological chromatography analysis indicated that the characteristics of gas composition were different under different electron donor conditions.N₂and N₂O were detected in the gas produced by strain SZ28,and Cd(?)could inhibit the production of N₂when ZVI and n ZVI were used as electron donor,while Cd(?)in the medium of Fe(?)and Mn(?)showed not remarkable effect on gas emissions.Moreover,characterization of extracellular polymeric substances(EPS)produced by strain SZ28under different conditions was analyzed.Results showed that the maximum concentration of carbohydrates was higher than that of proteins under any electron donor conditions.Moreover,in the presence of Cd(?)in the medium,the proteins contents would increased.In addition,sequence amplification identified the presence of the nap A and cum A gene in strain SZ28.XRD,SEM analysis showed that in the process of denitrification,the product of ZVI as the electron donor was Fe₃O₄and Fe OOH;the product of n ZVI as the electron donor was Fe₃O₄,Fe₂O₃and Fe OOH;the product of Fe(?)as the electron donor was Fe OOH and the product of Mn(?)as the electron donor was MnO₂.XPS spectra indicated that the Cd(?)was adsorbed onto biogenic precipitation.(3)The Fe₃O₄@Cu/PVA biofilm reactor was established.Effects of some key factors Mn(?)concentration(10mg/L,40mg/L,60mg/L),Cd(?)concentration(10mg/L,20mg/L,30mg/L)and HRT(6h,8h,10h)on Fe₃O₄@Cu/PVA denitrification were investigated in lab-scale bioreactors.Meanwhile,without material as a contrast,the enhancement of denitrification and Cd(?)removal efficiency of Fe₃O₄@Cu/PVA in a mixotrophic microbial reactor was studied.In the control reactor,the highest nitrate and Cd(?)removal ratios(100.00%and 98.34%,respectively)were observed at the Cd(?)concentration of 10mg/L,Mn(?)concentration of 40mg/L and HRT of 10h.Compared with the reactor without adding material,the denitrification efficiency,Mn(?)oxidation efficiency and Cd(?)removal ratio of the experimental reactor were increased by 6.72%,25.80%and 10.08%,respectively.(4)The novel PPy@Fe₃O₄/PVA biomaterials as new adsorbents and bacterial cell immobilized carrier were synthesized in this work.The optimum PPy@Fe₃O₄/PVA concentrations(300mg/L)and stability material cycles were confirmed,the composition and degree of crystallinity of the PPy@Fe₃O₄/PVA was analyzed by means of SEM and XRD.Mixotrophic biofilm reactor was established,and three factors(Mn(?)concentration,Cd(?)concentration and HRT)were investigated for Cd(?)and nitrate removal in the mixotrophic cultivation.Results showed that the optimum conditions were as follows:Cd(?)concentration of 10mg/L,Mn(?)concentration of 40mg/L and HRT of 10h.Under this condition,the maximum nitrate and Cd(?)removal ratio were100%and 94.34%,respectively.