Organic suspended matter and microorganisms in seawater at seven salt-making factories by ion exchange membrane were studied toexamine the effect of sand filtration as pretreatment of feeding coastal seawater.Amount of suspended matter in feeding seawater varied with seasons and locations where salt-making factories exist. However, similar compoSition of suspended matter was found in pretreated seawater among seven factories. More than 95% of suspended particles larger than 25μm were removed from feeding seawater through pretreatment of one or two steps of sand filtration. As a result, weight of suspended matter and concentration of chlorophyll a, particulate organic carbon and particulate organic nitrogen decreased markedly in pretreated seawater. Medium size particles (5-25μm) were also effectively removed through sand filtrations. Amount of the particles was ranged around 103/ml in pretreated seawater. Almost same order of smaller suspended matter was detected in feeding and pretreated seawater; 105-106/ml of direct count of bacteria, 103-104/ml of viable count of bacteria, and 104/ml of particles smaller than 5μm. Development of new pretreatment system which is effective for removing small suspende dmatter would be desired for substituting for sand filtration, if microorganisms and small organic or inorganic suspended matter which pass through sand filtration would deposit on the surfaces of ion exchange membranes and reduce the effciency of seawater concentration processes.
Organic matter and microorganisms deposited on the surfaces of ion exchange membranes were studied to elucidate the mechanism of deposition at seven salt making factories.Deposited matter was always found abundantat seawater entrance part of spacers,which was placed between cation and anion exchange membranes.There are no considerable differences on the amount of microorganisms and deposited matter,and their chemical components between on the cation and the-anion exchange membranes. Viable counts of bacteria in the deposited matter were104-105/cm2 and 105-106/mg.Amount of chlorophyll a was very low,less than0.02μg/cm2.Dominant bacteria flora deposited on the membranes was composed of dominant groups in coastal seawater where each factory located. Filamentous microorganisms which spread every direction were observed under microscope with the stained preparations of the deposited matter.The microorganisms were found in all the samples examined. First step of deposition is thought to be attachment and growth of bacteria on the membrane surface.Then,matrix of deposited matter would be gradually formed as inorganic particles and fragments of phytoplankton are being trapped on the“primary film.”