Factors influencing critical flux of UF membrane in drinking water treatment

Very few fouling or even no fouling would happen when ultrafiltration (UF) was operated below the critical flux. Factors influencing the critical flux of UF for drinking water treatment were systematically investigated in both short-term and long-term tests. Results showed that critical flux could be increased by 5 L/m2 h by continuous aeration with the air flow rate of 10 m3/m2 h, and the same effect could be obtained by intermittent aeration with the air flow rate of 40 m3/m2 h which could not be further improved by increasing air flow rate. Intermittent filtration had no positive effect on improving critical flux, while intermittent filtration combined with aeration could effectively improve critical flux by 5 L/m2 h and reduce fouling a lot in long-term filtration. Critical flux could be increased by 10 L/m2 h when coagulation and sedimentation pretreatment was applied, and could be increased by 15 L/m2 h for combined process of coagulation combined with continuous aeration or coagulation combined with intermittent filtration and intermittent aeration. Coagulation coupled with intermittent filtration and aeration would produce a synergy effect on critical flux improvement. Critical flux determined by flux-step tests could help to instruct the UF operation in application.