Role of backwash water composition in alleviating ultrafiltration membrane fouling by sodium alginate and the effectiveness of salt backwashing

To obtain a better hydraulic cleaning strategy for ultrafiltration (UF) membranes fouled by sodium alginate (SA), various types of backwash water, including UF permeate, ultrapure water, NaCI solution, CaCl2 solution and SA solution, were compared with respect to hydraulic cleaning efficiency (HCE), hydraulically irreversible fouling index, Fourier transform infrared spectra analysis, normalized transmembrane streaming potential coefficient and foulant release. The results indicated that UF permeate backwash or CaCl2 solution backwash significantly decreased the HCE. On the contrary, NaCI solution backwash greatly alleviated the SA fouling, and backwashing with ultrapure water or organic compounds was also efficient when both Na+ and Ca2+ were present in feed water. Moreover, the amount of released SA from the fouling layer during backwashing was closely related to that of released Ca2+. Electric double layer release involved in backwashing with ultrapure water and SA solution, and ion exchange played significant roles in the effective hydraulic cleaning associated with Na+ Further, monovalent salt backwashing was quite effective for a wide range of salt concentrations, and the approach was effective irrespective of monovalent salt types. Moreover, the results obtained from natural organic matter (NOM) and effluent organic matter (EfOM) further proved the efficiency of NaCI solution backwash. (C) 2015 Elsevier B.V. All rights reserved.