Washing performance of microbubbles on porous media

The backwashing effect of filter materials in oilfield wastewater treatment processes is essential for the efficient long-cycle operation of equipment and the reduction of hazardous waste. Recently, there has been growing interest in microbubble cleaning technology due to its exceptional cleaning efficiency for porous particles. However, the mechanism of microbubble-pore interaction and its corresponding cleaning effects remain unclear. This study investigated the performance of microbubbles in removing petroleum hydrocarbon pollutants from walnut shells, comparing them with traditional water washing and state-of-the-art ultrasound methods. Microbubble cleaning proved most efficient in removing low-viscosity petroleum hydrocarbons, followed by ultrasonic waves, both of which showed significantly higher efficacy compared to traditional water washing. When treating petroleum hydrocarbon pollutants with high viscosity, microbubble cleaning was more effective than clear water but slightly less effective than the ultrasonic wave method. Based on the analysis of clogging phenomena observed via scanning electron microscopy (SEM), the mechanism of microbubble cleaning within porous media was unveiled. Microbubbles were found to be proficient at dislodging contaminants adsorbed within secondary pores through collision and the force generated by liquid jets, as well as penetrating the small pores to eliminate pollutants from these inner spaces. Finally, an economic cost analysis of the various cleaning methods revealed that the microbubble approach is a cost-effective choice for the removal of light oil or the situations where a relatively lower removal efficiency for heavier oils is acceptable.