Experimental Study On The Remediation Of Acid Coal Gangue By Sulfate-Reducing Bacteria Citrobacter Sp. Strain YS1

Under the combined effects of long-term natural oxidation,precipitation leaching,and microorganisms,open-air coal gangue will oxidize and produce acidic mine drainage（AMD）.The heavy metals and sulfates released by coal gangue enter the soil,surface water,and groundwater with AMD,posing a serious threat to the surrounding ecological environment.In this thesis,in order to solve the problem of acid pollution in the coal gangue dump,a sulfate-reducing bacteria Citrobacter sp.strain YS1 was isolated from the sediment polluted by the leaching of gangue for a long time.After its molecular biological identification,the remediation experiment of acid coal gangue was carried out,and the inhibitory effect of strain YS1 on the release of sulfate and heavy metals was discussed.The dynamic simulation experiment system of microbial remediation of coal gangue was carried out by using strain YS1.The main conclusions of the thesis were as follows:（1）A sulfate-reducing bacteria was isolated from the sediment contaminated by acid gangue leaching for a long time.It was identified as Citrobacter by 16S r RNA gene sequencing and named Citrobacter sp.strain YS1（NCBI accession number:ON527765）.After growing in the liquid medium containing Fe²⁺for 1-3 days,the bacteria liquid was black,and the colonies in the solid medium were round,with neat edges,convex bulges,thick,and 1-3 mm in diameter.The strain is rod-shaped,with periflagella and a size of（0.5-0.6）μm×（2.0～2.2）μm.The sequence of its dissimilatory sulfite reduction gene（dsr AB gene）was similar to that of the traditional sulfate-reducing bacteria Desulfovibrio.（2）The growth and sulfate reduction characteristics of Citrobacter sp.strain YS1were explored.When inoculated with YS1 liquid culture at a 5%vaccination ratio,its growth experienced four stages:delayed phase（0-28 hours）,logarithmic phase（29-61hours）,stable phase（62-76 hours）,and decay phase（after 77 hours）.Strain YS1 has wide growth conditions and high reduction efficiency for SO₄^2-.It can grow and reduce SO₄^2-in the p H range of 5.0～9.0,temperature range of 20～45℃,and SO₄^2-concentration range of 500～5500mg/L.The highest reduction efficiency for SO₄^2-can reach 85.19%.In addition,different from the traditional sulfate-reducing bacteria,strain YS1 grew more vigorously under aerobic conditions than under anaerobic conditions and can still reduce 49.84%of sulfate.（3）Strain YS1 can effectively repair the acidic pollution of coal gangue and inhibit the release of heavy metals.When using sodium lactate as a carbon source,YS1 can increase the p H value of the gangue leaching solution from 5.45 to 7.88,and achieve a reduction rate of 81.67%for SO₄^2-in the gangue leaching solution.Zn,Cu,and Cd were not detected in the leaching solution,and the concentrations of Mn,Al,Ni,and Fe were reduced by 99.78%,98.58%,98.75%,and 99.95%compared to the control group,respectively.（4）The remediation mechanism of strain YS1 on acidic and heavy metal pollution of coal gangue was explored.XRD and SEM analysis showed that under the action of strain YS1,the microcosmic morphology of the coal gangue surface was changed.S^2-generated by the reduction of sulfate combined with metal ions to form solid sulfide on the surface of coal gangue,which slowed down the oxidation of pyrite in coal gangue.XPS analysis showed that S in the gangue showed the conversion from S⁶⁺to S^2-and S₂^2-and Fe showed the conversion from Fe³⁺to Fe²⁺under the remediation effect of YS1,which verified the sulfate reduction process.FTIR analysis showed that the hydroxyl and amino groups in surface polysaccharides,proteins,and lipids were involved in the complexation with heavy metal ions in the gangue and leachate.（5）The fermentation broth of corncob,bran,chicken manure and straw fermented for 10 days was used as a composite carbon source,and then an experimental system for microbial remediation of acid coal gangue was constructed.The results of the 30days remediation experiment showed that the system could increase the p H of the coal gangue leachate from 4.37 to 7.42,and the final SO₄^2-concentration decreased by 992.6mg/L compared to the control group.At the same time,it also significantly inhibited the release of heavy metals.During the repair process,the relative abundance of some acidophilic oxidizing microorganisms sharply decreased,and the Citrobacter genus gradually became the dominant bacterial group.Its relative abundance increased from17.87%（5d）to 58.75%（10d）,reaching a maximum of 78.98%（30d）,indicating that Citrobacter sp.strain YS1 can be applied to the remediation of acidic coal gangue pollution.