Changes in natural organic substances and microbes in sea water at each process of the ion-exchange membrane salt-making system were examined annually to elucidate the depositing mechanism of adherent dirt on the ion-exchange membrane. Organic substances and microbes in feeding sea water were effectively removed through two consecutive sand filtrations. However, the removal rate for polysaccharide in feeding and pretreated sea water did not meet the expected level(it decreased to 20 - 60 % of that in feeding sea water). There were no considerable differences in the amount of and the composition of organic and inorganic substances and microbes deposited between the anion and the cation exchange membranes. The establishment of an effective removal system of polysaccharides loaded newly in the sand-filtration process as well as those derived from feeding sea water will be required for the suppression of ion-exchange membrane fouling in ion-exchange membrane salt-making facilities. Also, in this research it was found that(1)bacteria in adherent dirt on the membrane have a high tolerance to antibacterial and bacteriostatic agents compared to those in feeding sea water, and(2)it requires attention to biological contamination of washing solution and cleaning tools for ion-exchange membrane.
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