Efficient adsorption of organic matters and ions by porous biochar aerogel as pre-treatment of ultrafiltration for shale gas wastewater reuse

Abstract

The large amounts of flowback and produced water (FPW) generated from the shale gas extraction process have characteristics of high salinity and complicated organic matters. It is challenging to treat and reuse it economically. We have verified the reliability of powdered activated carbon (PAC)-ultrafiltration (UF) pre-treatment in treating FPW for reuse in our previous work. To further enhance adsorption efficiency, we employed porous biochar aerogel (PBA) adsorbent to the field of shale gas wastewater treatment for the first time. The PBA synthesized from carbonized chitosan in alkaline solution exhibited three-dimensional porous structure and abundant functional groups. The adsorption of dissolved organic carbon (DOC) in FPW adsorption onto PBA followed the Freundlich isotherm model and pseudo-second-order kinetic model. The PBA adsorbed 52.5% DOC from FPW in just 30 min, which was 2.1 times that of the PAC. Meanwhile, the PBA showed stronger selective adsorption for monovalent ions such as Li+ Na+, Cl−, Br−, and F− than PAC. Besides, the UF membrane fouling caused by pollutants from FPW was reduced owing to PBA adsorption pre-treatment. PBA can reduce UF membrane fouling by 46.8%. Because of its fast and efficient adsorption performance, PBA has tremendous potential in improving the efficiency of FPW treatment.