Variation characteristics of typical ions and trace elements and health risk assessment in the process of coal gasification by microorganism

Methane can be produced by adding microbial communities and nutrients to the coal seam.In the microbial utilization of coal and nutrients,the concentration changes of typical ions and trace elements are related to the safety of the surrounding environment.Coal samples from Pingdingshan,Yima and Changzhi were selected to carry out some simulated biogas experiments to study the liquid phase change characteristics of trace elements in the process of coal biogas.The concentrations of Na+,NH4+,K+,Cl-,and PO3-4,which are major ions in the liquid phase of biological gas production from coal,were determined by ion chromatography (IC).The mass concentrations of V,Cr,Mn,Co,Ni,Cu,Zn,As,Se,Ag,Cd,Sb,Ba,Ti,and Pb were determined by inductively coupled plasma mass spectrometry (ICP-MS).The results show that the contents of major ions in the liquid phase were stable with the increase in gas production time.A strong correlation existed between the changes in trace elements and gas production.V,Ag,and Cd were not detected,but the mass concentrations of As,Ba,Co,Ni,and Pb increased with the prolonged biological gas production time from coal.The concentration changes of Pb,Se,and Ti were related to coal samples.The content of Ba was the highest at 23.88-144.79 μg/L,whereas the concentration ranges of As and Cu were 5.88-25.07 and 5.47-14.17 μg/L,respectively.The contents of other metal elements were low.Ten days before the coal immersion experiment,the contents of Ba,Cu,Ni,and Se in the solution increased gradually.The results of health risk assessment showed that the risk range of non carcinogenic substance,namely,Pb,Ni,Cu,and Ba was between 4.37×10-12 and 1.48×10-9 per year,which was considerably less than the non carcinogenic risk threshold of 1.The non carcinogenic risk of Cu was higher than that of the other three metals.The carcinogenic risk of As was between 4.61×10-5 and 1.96×10-4 per year,which exceeded the carcinogenic risk threshold of 1×10-6.Thus,As was the most harmful potential pollutant to health in coal gasification and should be given research attention.