Application of ultrafiltration hybrid membrane processes for reuse of secondary effluent

This study evaluates the factors affecting pretreatment conditions for hybrid UF membrane processes for reuse of secondary effluent from the sewage treatment plant. The experimental results obtained from the ultrafiltration (UF) membrane process showed that the particles of the size range between 0.2 and 1.2 mm caused a significant impact on membrane fouling in all cases even with or without the coagulation process. As pretreatment of UF membrane process, the coagulation significantly improved the permeate flux. Optimal flux improvement was seen at an alum dose of 50 mg/L. In addition, it was found that the permeate flux was least declined under the coagulation condition of charge neutralization (pH 5.0). Also, the powdered activated carbon (PAC) adsorption enhanced the permeate flux. Application of the direct filtration as a pretreatment of UF membrane process was also very effective in reducing the UF membrane fouling.

In this study, we found that the particles of the size range of 0.2–1.2 mm caused a significant impact on membrane fouling in all cases with or without the coagulation. When coagulation pretreatment was used as a UF hybrid membrane process, an alum dose of 50 mg/L presented the least reduction in membrane fouling. The result of the permeate flux on coagulation pH indicated that pH 5.0 showed a flux decline lower than other pH conditions. These results led us to conclude that the permeate flux was least declined under the condition of charge neutralization (pH 5.0). When PAC addition as a pretreatment was used as a UF hybrid membrane process, the PAC dose of 100 mg/L showed the lowest flux decline, followed by 50 and 150 mg/L. In addition, applying the direct filtration as a pretreatment of UF membrane process was very effective in reducing the UF membrane fouling. Thus, the coagulation process alone or the direct filtration can be retrofitted to a pretreatment of UF membrane process. Therefore, these hybrid UF membrane processes can be applied for direct reuse of secondary effluent as a type of urban reuse, agricultural reuse, landscape and industrial reuse or as a pretreatment before a second step of a reverse osmosis membrane process.