The Role of Coagulation and Microfiltration in Seawater Pre-treatment

Abstract

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 /(m² h) at the initial stage and 2500 L/(m² 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 μm 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 (~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.