title: Towards a better hydraulic cleaning strategy for ultrafiltration membrane fouling by humic acid: Effect of backwash water composition.
abstract: As a routine measurement to alleviate membrane fouling, hydraulic cleaning is of great significance for the steady operation of ultrafiltration (UF) systems in water treatment processes. In this work, a comparative study was performed to investigate the effects of the composition of backwash water on the hydraulic cleaning performance of UF membranes fouled by humic acid (HA). Various types of backwash water, including UF permeate, Milli-Q water, NaCl solution, CaCl2 solution and HA solution, were compared in terms of hydraulically irreversible fouling index, total surface tension and residual HA. The results indicated that Milli-Q water backwash was superior to UF permeate backwash in cleaning HA-fouled membranes, and the backwash water containing Na(+) or HA outperformed Milli-Q water in alleviating HA fouling. On the contrary, the presence of Ca(2+) in backwash water significantly decreased the backwash efficiency. Moreover, Ca(2+) played an important role in foulant removal, and the residual HA content closely related to the residual Ca(2+) content. Mechanism analysis suggested that the backwash process may involve fouling layer swelling, ion exchange, electric double layer release and competitive complexation. Ion exchange and competitive complexation played significant roles in the efficient hydraulic cleaning associated with Na(+) and HA, respectively.
authors.affiliation: State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China.
authors.forename: Haiqing
authors.initials: H
authors.lastname: Chang
authors.affiliation: State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China.
authors.forename: Heng
authors.initials: H
authors.lastname: Liang
authors.affiliation: State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China. Electronic address: changingchq@126.com.
authors.forename: Fangshu
authors.initials: F
authors.lastname: Qu
authors.affiliation: State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Ma
authors.affiliation: State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China.
authors.forename: Nanqi
authors.initials: N
authors.lastname: Ren
authors.affiliation: State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China.
authors.forename: Guibai
authors.initials: G
authors.lastname: Li
mesh_terms: D006812:Humic Substances; D008567:Membranes, Artificial; D014462:Ultrafiltration / Q000379:methods*; D018508:Water Purification / Q000379:methods
chemical_list: D006812:Humic Substances; D008567:Membranes, Artificial
keywords: Backwash water composition; Humic acid; Hydraulic cleaning; Membrane fouling; Ultrafiltration