Natural bentonite used as low-cost adsorbent for the adsorption pretreatment of coal gasification wastewater: performance comparison and component analysis

Natural clays have the characteristics of wide source, low price, large specific surface area and complex porous structure, and also possess a certain adsorption ability for organics in wastewater. In this study, bentonite (BTT), attapulgite, diatomite and volcanic rock were applied as adsorbents for the pretreatment of coal gasification wastewater (CGW) by batch experiments. Results showed that BTT had better removal performance on chemical oxygen demand (COD), ammoniacal nitrogen (NH3-N), etc. in CGW after comparison, and the removal efficiencies of COD, NH3-N, total organic carbon and total phenol could reach 28.1%, 33.5%, 33.9% and 39.6%, respectively. The biodegradability of CGW has been improved after BTT adsorption, and the biochemical oxygen demand (BOD5)/COD ratio increased from 0.31 to 0.37. Meanwhile, the toxicity of wastewater has been significantly reduced, and the reduction efficiency reached 31.8%. Additionally, the results of kinetics and isotherms implied that the adsorption of organic pollutants is mainly by the monolayer adsorption and diffusion-controlled physical adsorption of BTT. Specifically, the effect of pretreatment is mainly reflected in the adsorption of phenolic pollutants, and the removal of major phenols is the main reason for the reduction of CGW toxicity and the improvement of biodegradability. Hence, BTT as a low-cost adsorbent can provide insight into the wide application of CGW pretreatment.