The Role of Coagulation and Microfiltration in Seawater Pre-treatment

Power industry needs make-up water in power plant processes to compensate for the constant water loss during work. Mediterranean Seawater samples are studied to obtain pretreated water to use as a feed for the desalination stage. A comparison of coagulation with two coagulants, namely Poly aluminum chloride and ferric chloride in a one wt% stock solution, followed by microfiltration, was evaluated to obtain an efficient pre-treatment method. The lowest dosage of PACl positively affected all the measured parameters, especially the total suspended solid content was reduced to below 10 mg/L. The addition of FeCl3 resulted in 2.5-times higher total suspended solid content (23.5 +/- 4.58 mg/L) than the initial value measured for seawater (10.8 +/- 1.03 mg/L). Considering the flux values, two-steps of microfiltration and the lowest dosage of PACl followed by microfiltration resulted in the same high flux (3500 L /(m(2) h) at the initial stage and 2500 L/(m(2) h) at the 90% recovery rate). The flux after FeCl3 dosage seemed to be the highest, but it should be emphasized that the flocs were filtered via two consecutive 5-13 mu m microfiltration stages, so this flux is not entirely comparable with those measured in other cases. Considering the chloride concentration, after microfiltration without coagulation, it remained constant; using coagulants it showed a slight reduction (similar to 4%). From environmental point of view, the two-steps of microfiltration is recommended to be used since no chemicals are required for the operation; it can provide a steady flux of the cleanest pretreated water based on total suspended solid content.