The Mechanism Of Bio-oxidation Combined With Carbonate Neutralization On Fe²⁺ Oxidation And TFe Removal From AMD

The problem of water environment pollution caused by Acid mine drainage(AMD)has become increasingly prominent.In this paper,the high-throughput sequencing Mi Seq technology was used to analyze the function of bacteria and variation characteristics of bacterial community structure in an AMD system using carbonate rocks as the reaction medium in Guizhou province.This study used the iron oxidizing bacteria liquid obtained from the leaching liquid of the mine yard to explore the influence mechanism of the carbonate rock on the Fe²⁺biological oxidation and the biocatalytic secondary mineral synthesis in the acid sulfate system by the shake flask experiment.The formation of biofilm on the surface of polypropylene three-dimensional elastic filler is used to construct a combined treatment system of biological oxidation and carbonate rock neutralization to simulate the dynamic experimental study of AMD.The results of this study can provide basic data reference for the process and method construction of the combined treatment of AMD by biological oxidation and carbonate neutralization.(1)The characteristics of bacterial community structure in a system of treating AMD with carbonate rock as the reaction medium in GuizhouProteobacteria and Chloroflexi were the preponderant populations,while90.95%of Cyanobacteria existed in suspended matters of reaction cell.The structure of bacterial community was affected by the concentration of heavy metals in sediment,but the influence of Fe,Ni,As and Pb was especially distinct.There were significant differences in bacterial communities between the front part(inlet and reaction cell)and the back part(sedimentation cell and constructed wetland)of the system.The bacterial?-biodiversity index in sediments increased along the processing flow direction.it was found that iron oxidizing bacteria including Gallionella and Sideroxydans and iron reducing bacteria involving in Geobacter and Rhodoferax mainly existed in the sediment of the multistage reaeration reaction cell.Additionally,pedomicrobium,which could accumulate iron and manganese oxides,was in wetland sediments and plant rhizosphere soil.The abundance of pedomicrobium(8.38%±1.51%)and Nitrospira(14.75%±0.46%)was higher in constructed wetland than that in multi-stage reoxygenation reaction cell.When the process combining multistage reoxygenation cell with vertical flow constructed wetland based on carbonate rock as the main reaction medium was applied to treat AMD,not only carbonate rock neutralization and precipitation but also biological oxidation and biological reduction all played important roles in removal of pollutants in AMD.(2)The influence of carbonate rock on Fe²⁺biological oxidation and secondary mineral synthesis in acidic sulfuric acid environmentThe results showed that the addition of 10 g and 30 g carbonate rocks did not have a significant effect on p H,ORP and Fe²⁺biological oxidation rate,but the removal rate of TFe increased from 37%to 55%and 62%respectively,and the mineral production also increased from 8.17 g·L^-1to 12.03 g·L^-1and 13.69 g·L^-1,respectively.Meanwhile,the secondary iron mineral phase synthesized in the system had no obvious change compared with that without carbonate rocks,and it was mainly a mixture of schwertmannite and jarosite minerals.With the addition of carbonate rocks to 50 g,70 g and 90 g,the p H in the system increased rapidly,the biological oxidation rate of Fe²⁺was inhibited,and a large amount of calcium sulfate with good crystallinity was produced.The iron minerals are mainly lepidocrocite and goethite.The addition of an appropriate amount of carbonate rocks could produce Ca²⁺and Mg²⁺in the system,thus affecting the synthesis of secondary iron minerals.Therefore,when using carbonate rocks as a reaction medium to treat acid coal mine wastewater,adding A.f.bacteria and controlling the dosage of carbonate rock could strengthen the biological oxidation of Fe²⁺and the synthesis of secondary minerals in the system,further improve the removal effect of TFe in the reaction system.(3)Study on construction of combined treatment system of biological oxidation and carbonate neutralizationBiological oxidation could effectively oxidize Fe²⁺in AMD with a Fe²⁺concentration of 593.67 mg·L^-1(40.18%-55.49%)than carbonate neutralization,but the removal rate of TFe was not good(5%-17.39%).Added a proper amount of carbonate rock to increase the p H(3.03-3.86)could not only effectively oxidize Fe²⁺(39.09%-52.64%),but also increase the removal rate of TFe(25.09%-47.33%).Carbonate neutralization could effectively increase the p H of AMD to about 6,but it was very slow to continue to increase the p H,the effect of Fe²⁺oxidation(24.72%-34.73%)is not good,but the effect of Fe³⁺removal is better.The secondary minerals in the sediments of the biological oxidation section of the carbonate rock were jarosite,schwertmannite and tetragonal lepidocrocite,while the secondary minerals in the sediments without the carbonate rock were mainly jarosite.A stable biofilm could be formed on the surface of the polypropylene three-dimensional elastic filler,which was mainly composed of microorganisms and sediments.The surface sediment of the filler with carbonate rock was a mixture of jarosite and schwertmannite,while the sediment on the filler surface with no carbonate rock was jarosite.In the water samples of the biological oxidation section,Acidithiobacillus and Leptospirillum dominate(accounting for more than 75%).It also had other bacterial communities which contained low-abundance Acidiphilium and Pseudomonas that had the ability to oxidize or reduce Fe and S.