Performance evaluation of pretreatment processes in integrated membrane system for wastewater reuse

A series of lab-scale filtration experiments were performed under various operating conditions to investigate the fouling behavior of microfiltration (MF) membranes when employing two different pretreatment methods. The secondary effluents from a biologically advanced treatment process were fed to each hybrid system, consisting of coagulation–flocculation–MF (CF–MF) and ozonation–MF processes. All experiments were carried out using a stirred-cell system, which consisted of polyvinylidene difluoride (PVDF) MF membranes with a 0.22 μm pore size. When MF membrane was used alone without any pretreatment, the permeate flux dropped significantly. However, in the case of employing polyaluminium chloride (PACl) coagulation and ozonation as a pretreatment, the extent of flux decline rates was enhanced up to 88 and 38%, respectively. In the CF–MF hybrid system, the removal efficiencies of COD and total phosphorus were significantly enhanced at a coagulant dose above 30 mg/L. With ozonation, more than 90% of the color was removed even at a low dosage of ozone (5 mg/L). Therefore, ozonation would be strongly recommended as a pretreatment in terms of removing organic matter. The permeate water quality by ozonation–MF process was in good compliance with the guidelines for wastewater reuse proposed by South Korean Ministry of Environment.