Characterisation and removal of organic matter from a reverse osmosis concentrate by a PAC accumulative countercurrent four-stage adsorption-MF hybrid process

A powdered activated carbon (PAC) accumulative countercurrent four-stage adsorption-microfiltration (ACFA-MF) hybrid process was investigated for the removal of dissolved organic matter from reverse osmosis concentrate (ROC). The results showed that based on the same PAC dose, the COD removal efficiency was improved to approximately 70% from 51% for a single-stage adsorption process and from 62% for the PAC accumulative countercurrent two-stage adsorption-MF (ACTA-MF) process, and the DOC removal efficiency increased to >80% from 55% and 70%, respectively. From another perspective, to achieve the same effluent quality (DOC removal efficiency of 83%), the PAC dose for the ACFA-MF process was 58% and 32% lower than that of a single-stage adsorption and the ACTA-MF processes, respectively. In addition, compared to the ACTA-MF process, membrane fouling was effectively mitigated by the ACFA-MF process. XAD-8 and XAD-4 resin fractionation and fluorescence excitation-emission matrix were also conducted to characterize organic matter in the ROC. The main emerging and priority pollutants could be removed in different degrees by the ACFA-MF process.