IMPACT OF ULTRAFILTRATION OPERATING-CONDITIONS ON MEMBRANE IRREVERSIBLE FOULING

The main limitation of the ultrafiltration (UF) process identified in drinking water treatment is membrane fouling. Although adsorption of n atural organic matter (NOM) is known to cause irreversible fouling, op erating conditions also impact the degree of irreversible fouling. Thi s study examined the impact of several operating parameters on fouling including flux, concentrate velocity in hollow fibers, backwash frequ ency, and transmembrane pressure. A hydrophilic cellulose derivative m embrane and a hydrophobic acrylic polymer membrane were used to conduc t these tests. Pilot testing showed that when shea-term reversible fou ling was limited during a filtration cycle by increasing the concentra te velocity, reducing the flux, and increasing the backwash frequency, the evolution of the membrane toward irreversible fouling could be co ntrolled. It appeared that operating parameters should be adjusted to maintain the increase of transmembrane pressure below a certain limit, determined to be approximately 0.85 to 1.0 bar for the tested UF memb rane, in order to minimize the rate of irreversible fouling. This thre shold for transmembrane pressure was confirmed empirically by compilin g data from over 36 pilot studies. Other testing results demonstrated that hydraulic backwash effectiveness decreased as the transmembrane p ressure applied in the previous filtration cycle increased. Backwash e fficiency in terms of membrane flux recovery after hydraulic backwash was reduced by 50% when the transmembrane pressure was increased from 0.4 bar to 1.4 bar.