Microbial Induced Carbonate Precipitation For Removal Of Heavy Metals And Biological Nitrogen Removal

In this study,a highly efficient simultaneous heterotrophic denitrifying biomineralization strain CN86(Acinetobacter)was selected to study the simultaneous removal of Cd²⁺,NO₃^--N and hardness factors,biological denitrification characteristics,biological denitrification product characteristics,the removal ability and removal mechanism of Cd²⁺,the removal characteristics of Cd²⁺by bioreactor,the influence of mixed electrons on denitrification of strains,and the mechanism of inducing precipitation of calcium carbonate.Suggesting that:(1)In different organic substances(sodium succinate,sodium acetate,glucose,and calcium acetate),initial Cd²⁺concentrations(0,9,13,17,21,and 25 mg/L)and p H(5.0,6.0,7.0,8.0,and 9.0)analyze the effect of environment factors under conditions.The results showed that sodium succinate was used as the carbon source,and the initial Cd²⁺concentration was 10 mg/L and the initial p H was 7.0.Under the optimum conditions,the Cd²⁺removal ratio was 100.00%,the NO₃^--N removal ratio was 89.85%,and the Ca²⁺removal ratio was 71.63%.The Cd²⁺removal mechanism was explored by setting addition/non-addition of Ca²⁺and constant/non-constant p H control experiments.It was found that the removal of Cd²⁺was affected by the co-precipitation with calcium carbonate and p H,and the co-precipitation to remove Cd²⁺played a major role.In addition,XRD and XPS analysis indicated that Cd²⁺in the solution environment could be converted to precipitate removal by the CN86 strain.Gas detection showed that99.94%of N₂ was detected in the gas produced by strain CN86.(2)Yulong filler biofilm reactor organisms were established with Acinetobacter sp.CN86,and different initial Cd²⁺concentrations(10 mg/L?30 mg/L?50 mg/L)were studied,with different initial p H(6.0?7.0?8.0).And different HRT(4h?6h?8h)on the biological nitrogen removal of Yulong filler biofilm reactor,removal of Cd²⁺and removal of Ca²⁺characteristics.At the same time,the Yulong filler group without the membrane was used as a control.The results showed that when the initial concentration of Cd²⁺was 10 mg/L,the initial p H was 7.0,and the HRT was 8 h,the effect of removing nitrate,Cd²⁺and Ca²⁺was the best in the reactor(the nitrate removal ratio was 99.13%,and the removal ratio of Cd²⁺).For 100%,the removal ratio of Ca²⁺is69.54%).At the same time,studies have shown that the strain can tolerate Cd²⁺with an initial concentration of 50 mg/L and still maintain a certain removal effect.The gas analysis of the gas produced by the reactor was carried out using a gas chromatograph.The results showed that the gas composition was 99.61%nitrogen,and no N₂O was detected during the reactor stabilization period.(3)The factors affecting the removal of Pb²⁺,NO₃^--N and Ca²⁺by Acinetobacter sp.CN86 were studied.Pb²⁺,Ca²⁺and NO₃^--N were removed by setting different initial Pb²⁺concentrations(0?5?10?20?30 and 40 mg/L)and different initial Ca²⁺concentrations(10?40?80?120 and 160mg/L)..The results showed that when the initial concentration of Pb²⁺was 5 mg/L and the initial Ca²⁺concentration was 160 mg/L,the effect of removal of nitrate,Pb²⁺and Ca²⁺by strain CN86 was the best(the nitrate removal ratio was 92.26%,the Pb²⁺removal ratio was 94.77%,and the removal ratio of Ca²⁺was 69.13%).Analysis of the bioprecipitate by XRD indicated that Pb²⁺was converted to a precipitate which was removed.Comparison of morphological differences between Pb²⁺-containing and Pb²⁺-free bioprecipitates using SEM analysis.(4)Setting up mixed electron donor experiments to study the effects of mixed electron donors(organic matter;organic matter+Fe²⁺;organic matter+Mn²⁺;organic matter+Fe²⁺/Mn²⁺)on nitrogen removal and biomineralization of strain CN86,and studies have shown that organic matter acts as an electron.Under the donor condition,the treatment effect was the best.The strain CN86 used Mn²⁺as the inorganic electron donor for denitrification and biomineralization,but the treatment effect was slightly poor(nitrate removal ratio was 83.33%,Ca²⁺removal ratio was 63.21%).The results also showed that the strain CN86 had a certain tolerance and ability to remove Mn²⁺(Mn²⁺removal ratio was 73.17%).Amplification by the polycopper oxidase cum A and MCO genes indicated that the strain CN86 had the ability to oxidize Mn²⁺.(5)Experiments on the effects of bacteria,EPS and bioprecipitation on biomineralization were set.The results indicate that it is necessary to promote carbonate formation under the biological action of strain CN86.The mechanism by which strain CN86 induces carbonate precipitation is that CN86 cells act as nucleation sites,the metabolism of strain CN86 produces CO₂,and CO₂ hydration produces CO₃^2-.The negatively charged groups on the surface of the cells can chelate Ca²⁺and further adsorb CO₃^2-.The organic matter in the culture medium is continuously decomposed by the strain CN86,so that the concentration of CO₃^2-in the solution is continuously increased,and the p H of the environmental solution is continuously increased,and the increase of the p H is more favorable for the formation of carbonate precipitation.Ca CO₃,which has been nucleated,continuously adsorbs Ca²⁺and CO₃^2-in the solution,and the precipitation increases.A gradient test was conducted to study the effect of carbon source on the removal of Ca²⁺by strain CN86 and the change of solution p H.The results showed that with the increase of carbon source,the effect of denitrification increased and the ratio of denitrification increased.At the same time,it was found that the p H increase of the unadded Ca²⁺group was greater than that of the added Ca²⁺group,which may cause environmental CO₃^2-due to carbonate precipitation induced by strain CN86.CO₃^2-decreases in concentration,which in turn affects p H rise.A continuous observation experiment of bioprecipitation was set up.It was observed by scanning electron microscopy that the increase of precipitation size with the increase of culture time enhanced the mechanism of the precipitation of carbonate by the strain CN86.