Experimental Study On Bioremediation Of Groundwater Polluted By Underground Coal Gasification

Underground coal gasification（UCG）is a technology of green coal mining,processing and transformation,but the risk of groundwater pollution is one of the main bottlenecks restricting its popularization and application.At present,the research on groundwater pollution caused by UCG mainly focuses on pollutant formation and prevention,while there is little research on pollution control,especially microbial remediation.In this paper,through the self-designed underground coal gasification simulation system and groundwater pollution bioremediation system,the underground coal gasification and its bioremediation of groundwater pollution are experimentally studied by means of GC-MS,ICP-MS,element analyzer,TOC analyzer and PCR.The main conclusions are as follows:Phenol and naphthalene,which are typical organic pollutants of UCG,were used as substrates to cultivate and screen two strains of highly effective phenol degrading strain Ga（belonging to Acinetobacter hospital）and highly effective naphthalene degrading strain Sa（belonging to Rhodococcus pyridinophilus）.The maximum degradation concentration of phenol and naphthalene can reach1500mg/L,respectively.The degradation rate of 500mg/L phenol and naphthalene can reach more than 95%.Study on degradation kinetics showed that the degradation of phenol by Ga conformed to Haldane’s substrate inhibition kinetic model,with the semi saturation constant K_S=24.41mg/l;the substrate inhibition coefficient Ki=136.84mg/l and the maximum specific growth rate V_M=0.42h^-1.The degradation of naphthalene by Sa conformed to the Monod’s growth kinetic model,with the maximum specific growth rate V_M=0.056h^-1and the semi saturation constant K_S=348.49mg/l.Through the study of degradation mechanism,three ways for Ga to degrade phenol and two ways for Sa to degrade naphthalene were put forward.The degradation of phenol by Ga is mainly through the ortho or meta ring opening pathway of hydroxylated catechol,and also through the carboxylated benzoic acid pathway in the middle and late stage of degradation.Sa degrade naphthalene via the phthalic acid pathway and the salicylic acid pathway,with the former being the major degradation pathway.The comparison of the degradation pathways of the two bacteria showed that Sa bacteria could also degrade phenol.Heavy metal copper and manganese ions could affect the degradation pathway of characteristic pollutants by degrading bacteria.In the presence of Cu²⁺,Ga degraded phenol by hydroxylation catechol meta ring opening pathway and carboxylation pathway.In the presence of Mn²⁺,the carboxylated benzoic acid pathway was the main pathway and hydroxylation pathway was the auxiliary pathway for phenol degradation.Sa degraded naphthalene through salicylic acid pathway and phthalic acid pathway,but the efficiency of the latter was significantly inhibited by heavy metals.The study on the influence and interaction mechanism of heavy metals on the degradation characteristic organic pollutants by degrading bacteria found that copper and manganese participated in the metabolism of degrading bacteria and accumulated inside and outside the cells.When the concentration of Mn²⁺is lower than 100mg/L,it has little effect on the degradation of characteristic organic pollutants.When the concentration of Cu²⁺exceeds 50mg/L,the growth of degrading bacteria and degradation of organic pollution are greatly affected.The removal rate of heavy metal copper and manganese by the two bacteria was more than 95%and 85%within 96 hours.Ga responded to heavy metal toxicity mainly through extracellular mechanisms,while Sa responded to both intracellular and extracellular mechanisms.Ga and Sa can grow in the compound polluted environment with the coexistence of various heavy metal ions and organic pollutants.After 96h of treatment,the average TOC of the compound polluted solution decreased by more than 50%,and the concentration of Pb,Cd and Cu decreased greatly,up to 99.9%.The mixture of the two bacteria is beneficial to reduce the concentration of heavy metal ions in the compound polluted solution.Ga,Sa and their mixture can effectively repaired the groundwater pollution caused by UCG.After 72h of degradation by Ga,Sa and their mixture bacteria,the TOC of gas washing water decreased by 88.25%,82.89%and 81.66%respectively,and the types of residual organic compounds decreased from 41 to 22,26 and 24 respectively,while their concentration also decreased significantly.After 120h of degradation by Ga,Sa and their mixed bacteria,the TOC of gasification ash soaking solution decreased by 65.12%,69.65%and 71.67%respectively,the high toxic organic pollutants such as phenols,quinolines and thiazoles disappeared,and the toxicity of organic compounds in the solution decreased as a whole.In the mixed polluted co matrix environment,Ga could completely degrade indole compounds within 72 hours,which might be based on the co-metabolism of phenol and indole and the synergistic mechanism between quinoline and indole.The degradation of quinoline compounds by Ga follows the pyridine ring opening pathway.Sa also have better degradation ability to phenolic pollution,and its degradation of quinolines exists in two pathways:benzene ring opening and pyridine ring opening.The mixed bacteria showed synergistic effects on the treatment and utilization of intermediates and end products,with stronger degreasing ability for heavy metal ions than single species,and showed a good remediation effect on groundwater contaminated by UCG.The dissertation includes 44 figures,32 tables and cites 178 references.