Simultaneously achieving high-effective oil-water separation and filter media regeneration by facile and highly hydrophobic sand coating

Abstract

Efficient oil-water separation, including of emulsified oil separation, is one of the problems restricting the green development of the petrochemical industry. Herein, highly hydrophobic sand was fabricated in one-step, followed by an investigation of adsorption capacity for various oils of hexane, petroleum ether, diesel, tetrachloroethylene and tetrachloromethane. The modified sand (MS) filter bed was subsequently set up to investigate the oil separation efficiency for oil-water mixtures, emulsions and actual petroleum refinery wastewater, respectively. Moreover, the capture process of the oil droplet by the MS was observed by a high-speed camera system, and the oil removal mechanism was explored. The removal feasibility of the oil adhered to the MS in a hydrocyclone was also investigated. The oil could be quickly adsorbed by the MS, and the adsorption capacity was positively correlated with oil density. A high flux of 14,436 L·m^-2·h^-1 and a considerable separation efficiency of 99% were obtained when the MS was applied for oil-water mixture separation. Additionally, the highest separation efficiency of various emulsions was up to 99.3%. Regrading actual petroleum refinery wastewater, the oil removal efficiency of the MS reached 90% rather than 57.8% of raw sand. The oil droplets in the wastewater were efficiently separated by the MS based on the mechanism of adsorption and coalescence. Additionally, the oil adhered on the MS could be removed, and the oil concentration decreased from 17.6% to 5.2%, which was ascribed to the MS spinning in a hydrocyclone. A novel oil-water separation method of hydrocyclone-intensified filtration by facile and highly hydrophobic sand coating was proposed, and simultaneously the filter media can be effectively regenerated. It is believed that this work might provide a low cost, recyclable and efficient strategy for oil removal, which shows high promise for industrial oily wastewater treatment.

Keywords: Adsorption capacity; Filter media regeneration; Highly hydrophobic sand; Hydrocyclone; Hydrocyclone-intensified filtration; Oil-water separation.