Microbial Degradation Of Naphthalene In Water Contaminated By Underground Coal Gasification

Underground gasification of coal（UCG）is one of the ways to achieve clean processing and utilization of coal,which is in line with the development direction of China’s energy transformation under the double carbon target and is of strategic importance to guarantee national energy security.However,the groundwater pollution generated by UCG has become a technical bottleneck limiting its application.In this paper,using naphthalene,a characteristic pollutant of underground gasification,as the carbon source,a microbial strain with efficient degradation performance of naphthalene was screened and domesticated from the groundwater of Jiaozuo Jiulishan mine,while an immobilized microbial pellet was prepared using fly ash as the carrier,and the growth characteristics of microorganisms and the degradation law of naphthalene by microorganisms and immobilized microorganisms were studied,and microbial remediation of simulated underground gasification wastewater was carried out.The main findings are as follows.A microbial strain capable of degrading naphthalene was isolated from the groundwater of Jiulishan Mine.The strain（KJS1）was identified as Rhodococcus＿sp.by physiological and biochemical experiments and 16Sr DNA identification.The highest activity of the strain was observed under the conditions of p H=6-10,30℃,initial naphthalene concentration≤700 mg/L,shaking speed of 160 r/min and Na Cl concentration≤2%.Growth kinetic studies showed that the bacterial growth rate increased with increasing naphthalene concentration.The GC-MS analysis of naphthalene degradation intermediates showed that Rhodococcus＿sp.KJS1 degraded naphthalene by the phthalic acid pathway,and Cu²⁺had a significant inhibitory effect on bacterial growth,while Mn²⁺had less effect on bacterial growth.The immobilized microbial pellets were prepared using fly ash as the carrier.5%（mass fraction）of Ca Cl₂,2%of fly ash,15%of bacterial solution amount and 5%of sodium alginate were the best preparation conditions for the immobilized microbial pellets.The optimal amount of naphthalene treated by the immobilized strain was 0.5 g/L,and the removal rate of naphthalene remained above 97%after 7 times of reuse.It was also found that the degradation ability of naphthalene by free strain was higher than that of immobilized strain under the condition of non-inhibited bacterial growth,and the degradation ability of naphthalene by immobilized strain was higher than that of free strain under the condition of inhibited bacterial growth.The microbial remediation experiments simulating coal underground gasification wastewater showed that the removal rates of TOC by free bacteria and immobilized strains were 59.1%and 29.2%respectively;after 96 h of microbial degradation,the phenolic pollutants in the wastewater were reduced from 14 to 2,quinolines,indoles,pyrimidines,pyridines and aromatics disappeared,and most of the toxic organic pollutants were degraded.Microbial remediation has good remediation ability for coal underground gasification polluted water.The dissertation includes 28 figures,15 tables,and 98 references.