Organics removal from ROC by PAC accumulative countercurrent two-stage adsorption-MF hybrid process - A laboratory-scale study

A powdered activated carbon (PAC) accumulative countercurrent two-stage adsorption-microfiltration hybrid process was investigated for the removal of organics from the reverse osmosis concentrate (ROC) produced in a refinery wastewater treatment plant. The results showed that approximately 70% of DOC was removed from the ROC; the effluent met the reverse osmosis (RO) influent quality requirement and could be further reclaimed by an RO system to improve the overall recovery rate by more than 90%; and >40% of the PAC dose was reduced compared to that in the conventional single-stage adsorption process. A calculation method for correlating the effluent quality with the PAC dose was calibrated, and the validity of the method was confirmed by a deviation of <5%. The dilution factor (F) affected the PAC dose and membrane fouling. The PAC dose at F = 0.3 was 14.46% lower than that at F = 0.5 based on the same effluent quality, but the membrane fouling was more severe in the former case. Analyses of the membrane eluent and SEM-EDS demonstrated that fine PAC particles adhering to the membrane surface and blocking the membrane pores dominated the irreversible membrane fouling process. Good correlations (R2 > 0.95) between the UV254 and DOC of the effluent could facilitate the operation monitoring of the process.