Hydraulic irreversibility of ultrafiltration membrane fouling by humic acid: Effects of membrane properties and backwash water composition

Five commercially available ultrabltration (UF) membranes: polyethersullone (PES, 100 kDa), polyvinylidene fluoride (PVDF, 100 kDa) and cellulose acetate (CA, 100, 30 and 10 kDa), were fouled with humic acid (HA) solutions and cleaned using various compositions of backwash water including ultra-pure water, monovalent cations (Na+), divalent cations (Ca2+), an organic compound (HA) and UF permeate. The hydraulically irreversible fouling and the hydraulic cleaning efficiency (HCE) for each combination of membrane and backwash water composition were analyzed. In summary, both the membrane properties and the backwash water composition affected hydraulically irreversible fouling. The membrane properties significantly affected the total fouling, and the HCE was primarily affected by the backwash water composition. Further, the adhesive free energy between HA and the membranes correlated well with the total fouling. Ultrapure water was superior to UP permeate for backwashing, and the presence of appropriate components (e.g., Na+ or HA) further improved the HCE; however, Ca2+ exerted detrimental impacts on the HCE. In addition, the removal of the deposited HA was consistent with the amount of Ca2+ released from the fouling layer during backwashing. Mechanistic analysis suggested that the backwashing process involves fouling layer swelling, ion exchange, electric double layer release and competitive complexation. (C) 2015 Elsevier B.V. All rights reserved.