Control fouling and cleaning procedures of UF membranes by a streaming potential method

Abstract

Abstract The impact of cleaning procedures on organic ultrafiltration (UF) membranes has been studied in terms of permeability, streaming potential (SP) and wettability. SP measurements of UF membranes are realised using a new design. This new design is more convenient to determine the SP for all kinds of modules (planar, hollow fiber, etc.). We used this design to control the efficiency of cleaning procedures. Furthermore, SP is used to determine the isoelectric points (IEPs) of two materials [polyethersulfone (PES) and cellulose triacetate (CTA)]. The IEPs were experimentally determined from SP variations with pH at a given ionic strength (0.001 mol l −1 ). The IEPs of both membranes studied are respectively 3.1 and 3.4. The study of the charge origin on the organic membranes showed that the adsorbing ions are those of water itself. In order to model the fouling with natural organic matter and to study the impact of cleaning procedures, the PES membrane was first modified by the surface adsorption of surface active agents (SAAs). For this purpose, a neutral (Triton X100, TX100) and a cationic [dodecyltrimethylammonium (DTAB)] SAA were studied. SAAs were used at a concentration in solution near that of CMC. The wettability of the fouled and virgin membranes was evaluated by means of contact angle measurements. An increase in the contact angle of a droplet deposited on the fouled membrane was correlated to a decrease in its permeability. Furthermore, the contact angle measurements show the acidic characteristic of the PES material at low pH. The use of β-cyclodextrin, a well-known host complexing agent for SAAs, was found to present a better efficiency to remove neutral SAAs than cationic SAAs, which are strongly bonded to the negatively charged PES membrane. The impact of cleaning procedures on CTA membranes fouled with Seine River water was evaluated in the light of these SP measurements. It appeared clearly that the streaming potential is a useful tool for the control of the membrane surface charge after cleaning procedures.