Effect of coagulation on MF/UF for removal of particles as a pretreatment in seawater desalination

Abstract

MF/UF has been recently applied as a pretreatment process due to its high removal efficiency of fouling matters in Reverse Osmosis (RO). This study evaluated the effect of coagulation on the performance of MF and UF for removal of particles with two kinds of membranes under various coagulant dose and pH. The efficiency was obtained by analyzing flux, turbidity and SDI 15 (Silt Density Index). MF membrane was used in determining the optimal coagulation condition in the coagulation– membrane system. For standard seawater with turbidity of 10 NTU, the optimum operation conditions were found at pH 8 with 0.5 ppm Fe as coagulant. It was obtained that the flux decline of membrane filtration was reduced when the membrane filtration was conducted with coagulation, compared to membrane filtration alone. At the same condition, SDI 15 of permeate from coagulation–MF and coagulation–UF were 0.75 and 1.88, respectively, that are less than the recommended value of 3, while SDI 15 of membrane permeate were 3.17 for MF only and 2.76 for UF only, respectively. At the optimal coagulation condition, membrane filtration combined with coagulation is proven to be an effective desalination pretreatment than membrane filtration alone. Between MF and UF, MF was more effective than UF for the enhancement of filtration flux and turbidity removal by applying coagulation as pretreatment method. In conclusion, MF and UF can be considered a good alternative pretreatment method in seawater desalination and lead to higher quality for RO feed with optimized coagulant condition.