Research On The Characteristics Of Iron Reducing Bacteria Coupled Heavy Metals Removal And Denitrification

In this experiment,high-efficiency iron reducing was purified to investigate the removal capacity of heavy metals and nitrate and the influence of various environmental factors on the removal of heavy metals and the progress of denitrification.In addition,immobilization reactors were established to study the removal characteristics of heavy metals and nitrates.The removal efficiency of Cd(?)is higher than other heavy metals with the source of iron was ferric citrate.The removal efficiency of Cd(?)and nitrate were 76.75%and 100%under the condition of 50.00 mg/L Fe(?),10.00 mg/L Cd(?)and 15.00 mg/L nitrate.At the same time,Fe3O4 powder was added to the pellet of the fixed reactor to investigate its effect on the removal of Cd(?)and nitrate.The results showed that the addition of Fe3O4 powder to the pellets can improve the removal ratio of Cd(?)and nitrate.When the influent Fe(?)concentration is 50.00 mg/L,the Cd(?)concentration is 10.00 mg/L and HRT is 12 h,The removal ratio of Cd(?)of group A(pellets combined with iron reducing bacteria)and group B(pellets combined with iron reducing bacteria and Fe3O4 powder)could reach the maximum(82.32%and 95.76%),and the nitrate removal ratio both reached 100%,respectively.The high-throughput sequencing method was used to analyze the microbial community composition and structure of different experimental groups of the bioreactor,which indicated that strain CC1 played a major role in the whole denitrification process.According to the comparative experiments,Cd(?)and Ni(?)revealed a higher removal ratio with divalent iron(ferrous sulfate)acted as iron source.In the environmental factors tests,the removal ratio of Cd(?),Ni(?)and nitrate increased with the increase of Fe(?)concentration.The highest removal efficiency of Cd(?)(86.65%),Ni(?)(57.86%)and the removal ratio of nitrate 100%was obtained at the conditions of the Fe(II)concentration of 15.00 mg/L,Cd(?)concentration of 10.00 mg/L,and nitrate concentration of 15.00 mg/L.Moreover,different inoculation(5%,10%,15%and 20%)and different C/N ratios(C/N=2,4,5,6 and 8)were also significant for the removal of Cd(?),Ni(?)and nitrates.The best removal efficiency of Cd(?),Ni(?)and nitrate was obtained with the inoculation amount was 10%and the C/N ratio was 5.The effect of pH(6.00,7.00 and 8.00),initial Fe(?)concentration(10.00,20.00 and 30.00 mg/L)and initial Cd(?)(Ni(?))concentration(10.00,30.00 and 50.00 mg/L)were analyzed by response surface methodology(RSM)to determine the effect on the removal of Cd(?)(Ni(?))and nitrate.The highest Cd(?)removal efficiency 96.83%and Ni(?)removal efficiency 90.63%occurred under the following conditions:pH of 8,30.00 mg/L Fe(?)and 10 mg/L Cd(?)(Ni(?));the highest nitrate removal efficiency(Cd(?))was obtained under the conditions of Fe(?)concentration of 22.35 mg/L,initial pH of 6.37 and Cd(?)concentration of 10.00 mg/L;the highest nitrate removal efficiency(Ni(?))was obtained with 21.37 mg/L Fe(?),pH of 6.57 and 10.00 mg/L Ni(?).Studies on the removal mechanism of Cd(II)and Ni(?)indicated that the removal of Cd(?)and Ni(?)is due to the synergistic effect of bacteria-Fe-oxides,the increase of pH during denitrification and the adsorption of extracellular polymeric substance.the adsorption of bacteria-Fe-oxides played the main role in the removal of Cd(?)and Ni(?),especially.X-ray diffraction(XRD)showed the main component of microbial precipitation is FeOOH.X-ray photoelectron spectroscopy(XPS)analysis proved that bioprecipitation can adsorb two heavy metals.The ?-CD@EDTA@Fe3O4 bioreactor and PDA@EDTA@Fe3O4 bioreactor were established respectively to study the effects of the Fe(?)concentration,Cd(?)concentration,Ni(?)concentration and different HRT on the removal of Cd(?),Ni(?)and nitrate.The results showed that the highest Cd(?)and nitrate removal ratios in the?-CD@EDTA@Fe3O4 bioreactor were observed with the Fe(?)concentration of 15.00 mg/L,the Cd(?)concentration of 10.00 mg/L,and the HRT of 10 h.The removal ratio of Cd(?)in the group A(only bacteria)was 83.70%,and the removal ratio of nitrate was 93.42%.Compared with group A,the removal efficiency of Cd(?)and the nitrate removal ratio were increased by 10.67%and 6.58%.In the PDA@EDTA@Fe3O4 bioreactor,the highest removal efficiency of Ni(?)and nitrate achieved at the optimum conditions:Fe(?)concentration of 20.00 mg/L,Ni(?)concentration of 10.00 mg/L and HRT of 10 h.Compared with group A(without materials),the removal ratio of Ni(?)and nitrate were increased by 19.46(92.55%)and 0(100%).Cupriavidus sp.CC1 is the dominant bacteria in the bioreactor.