The fouling was evaluated by the increase of transmembrane potential due to the increase of membrane electric resistance caused by biofouling. However, the voltage was not changed for 20h. Then, for further investigation, fouled membranes were then observed by scanning electron microscope -SEM-. SEM images showed a few bacteria attached on the membrane surface and the chang of the bacteria shape as shown in Fig. 1. Coverage percentage of bacteria obtained by analyzing the SEM images was 11.5%. Moreover, the biofouling was evaluated by a static adhesion test by dipping AMXs in P.putida, suspension -O.D.450 0.05- for 18 h in order to evaluate an effect of DC on biofouling. The coverage percentage was 22.5% in the static adhesion test. Although, the bacterium concentration under ED operation was 10 times higher than static adhesion test, the coverage percentage was smaller than that of static adhesion test. It means that the direct electric current suppressed bacteria attachment on AEM surface and biofouling may hardly occur in an ED operation.

Keywords