2.3. Cross-flow membrane test unit
A laboratory-scale cross-flow membrane test unit, depicted in Fig. 1, was used to measure the permeate flux [11]. A circular RO membrane was set in a cylindrical stainless steel membrane cell. The effect of operating conditions such as applied TMP and stirring rate in the cell was evaluated on biofouling which included the biofilm formation on the membrane surface and permeate flux decrease. Feed water was fed into the cell using a plunger pump (NPL-120; Nihon Seimitsu Kagaku Corporation, Tokyo, Japan) at 1 mL/min. The temperature of the feed reservoir and cell was kept at 30 °C using a water bath. The effective membrane area was 8.0 cm2. The feed water side in the cell was stirred by using a cylindrical magnetic bar of 3.0 cm length. The TMP was adjusted
by two back-pressure valves on the permeate and condensate water sides. The permeate flux was calculated from the weight of the permeate water measured using an electric balance.