| Acid mine drainage(AMD)generated by sulfur-rich coal gangue deposited in coal mining areas has posted a severely detrimental impact on soil and aquatic ecosystems.How to control the production of AMD and to eliminate its pollution to the ecological environment is an issue of great concern to the world today.Sulfate-reducing bacterium(SRB)have been demonstrated to be a promising treatment for AMD due to its alkali production and heavy metals stabilization ability.In this study,the effect of medium composition on heavy metal remediation and microbial community structure was explored,and the mechanism of heavy metal removal was also analyzed to establish a sulfate-reducing remediation system.To further verified the feasibility,effectiveness and stability of the sulfate-reducing system applied to acidic gangue pollution suppression and heavy metals removal,bottle experiments and dynamic column experiments were performed.The main purpose of this study was attempted to provide theoretical guidance and explore new engineering technology for the treatment of acidic gangue dumps.The main findings of this study are as below:(1)Sodium lactate,K2HPO4,Ca(HCO3)2 all favored the removal of heavy metals by sulfate-reducing bacteria,while ascorbic acid and MgSO4 did not show a significant effect.The best removal rates were obtained in the KP4 group,with high K2HPO4 concentration(2 g/L),which Fe(99.09%),Mn(89.25%),Al(100%),Co(100%),Ni(100%),Zn(100%)and SO42-(82.65%)were effectively removed.There was a significant positive correlation between the addition of K2HPO4 and Mn removal.The dissolution of Ca(HCO3)2 not only contributing to the removal of heavy metals,but also creating a suitable environment for the metabolism of SRB.(2)The dominated mineral phases of the microbial mineralization products were FeS and CaCO3,XPS analysis result showed 72.78%of Fe was transformed to FeS and vivianite(Fe3(PO4)2·8H2O),the rest were ferrihydrites and iron phosphate.Under heavy metal stress,the morphology of SRB cells was rough,wrinkled,and tightly adhered to polymers of nanoscale biomineralized particles.ATR-FTIR spectrum clearly showed that hydroxyl,amino,carboxyl,alkyl,and other functional groups on the SRB cell surface were involved in the complexation with heavy metal ions.(3)High-throughput analysis showed that Desulfovibrio and Desulfosporosinus were the main sulfate-reducing functional genera.Among them,the addition of sodium lactate could increase the abundance of Desulfovibrio.The addition of K2HPO4,as a phosphorus source required by some microorganisms,could effectively increase the microbial community diversity.The addition of Ca(HCO3)2 not only was helpful for the abundance increase of SRB,but also avoided the competition between Methanosarcina and SRB.(4)The gangue samples used in the experiment could reach a net acid production potential(NAPP)of 39.70 kg H2SO4 t-1 and net acid potential pH(NAGpH)of 2.24,which showed a strong acid production potential.Both biostimulation and bioaugmentation were able to raise the pH of the gangue leachate to neutral and remove heavy metals such as Al,Cd,Co,Cu,Ni and Zn,with removal rates above 89%and 69.03%for Fe and Mn.However,the results of the high-throughput analysis showed that the higher microbial community structure stability was obtained from biostimulation than bioaugmentation.The leaching toxicity analysis of coal gangue after microbial remediation showed the enhancement of heavy metals stability.(5)The dynamic column experiment showed that the sulfate reduction system could be successfully established within 28 days.Compared with the blank group CK,the bottom leachate pH of the remediation group CR column was increased from 1.57 to 6.71,and the removal of Al(100%),Cd(100%),Co(100%),Cu(100%),Fe(90.97%),Mn(64.07%),Ni(100%)and Zn(100%)was obtained,which successfully achieved the effective removal of pollution from acid-producing coal gangue. |
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