Determining flux behavior via a modified flux-step method for surface water treatment: pilot-scale ultrafiltration membrane operation

We present an alternative method for determining permeate flux behavior for membrane filtration of surface water. A modified flux-step method was developed and evaluated for two different submerged ultrafiltration membrane systems. Experimental results for a short-term pilot-scale system indicated that the modified method was able to determine the critical flux for irreversibility, improving on the conventional flux-step method. Using the modified method, the total membrane fouling rate and irreversible fouling rate can be used to simultaneously determine the threshold flux and critical flux for irreversibility. Based on the fluxes obtained in short-term tests, the long-term performance of the membrane system was also evaluated under operational conditions above the threshold flux and frequent variations in the turbidity of the surface water influent, combined with a cleaning regime. At a flux of 50 L/m2·h for membrane A and 40 L/m2·h for membrane B, the membrane fouling and fouling history were improved by cleaning through backwashing, draining of the membrane tank, and intermittent chemically enhanced backwash. Thus, by minimizing membrane fouling and transmembrane pressure increments based on the modified flux-step method, the membrane separation system cleaned using these methods achieved efficient surface water treatment under realistic operating conditions at high flux.