Experimental study on coagulation and adsorption treatment of wastewater in combustion cavity for underground coal gasification

Abstract

Underground Coal Gasification (UCG) is a promising mineral resource development technology that can transform in-situ coal into combustible gas by controlling combustion. However, wastewater generated during the UCG process can lead to environmental pollution in adjacent areas through diffusion or infiltration. In order to seek an efficient and inexpensive in-situ treatment method for underground gasification combustion zone wastewater, UCG model experiments were conducted to obtain wastewater, and the treatment effects of chemical coagulation and physical adsorption methods were compared in this work. The COD concentration in wastewater from underground combustion zone ranges between 555 ∼ 703 mg/L, with a pH value between 8.26 ∼ 8.85. The organic pollutants mainly come from the dissolution of high carbon components, mainly aromatic compounds in tar, which leads to high toxicity and pollution risk of wastewater. For chemical coagulation method, the removal effect of organic pollutants in combustion zone wastewater by ferric sulfate is better than that of aluminum sulfate due to excellent hydrolysis reaction of Fe3+. The corresponding COD removal rate and COD removal cost are 24.34 % and 0.176 ¥/g, respectively. For physical adsorption method, due to the large total pore volume and wide specific surface area of organic bentonite, it can effectively remove COD content. The COD removal rate and COD removal cost, and COD adsorption capacity are 60.23 %, 0.213 ¥/g, and 89.75 mg/g, respectively. Comprehensive comparison shows that physical adsorption is more suitable for in-situ treatment of combustion zone wastewater.