Abstract
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.
