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

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 SDI15 (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, SDI15 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 SDI15 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.

This study evaluated the effect of coagulation on the performance of MF/UF pretreatment with two kinds of membranes under various coagulant dose and pH. SDI15 values Fig. 10. Comparison of permeates from UF combined with coagulation and UF. of membrane filtration only were 3.17 and 2.76 for MF and UF, respectively. SDI15 of UF permeate met the recommended value of 3 while MF permeate had a resulting value a little higher than 3. With only membrane filtration, UF was more effective than MF as a pretreatment in desalination. In this study, it was found that optimum operating conditions were at pH 8 with coagulant dose of 0.5 mg/L as Fe in treating seawater with turbidity of 10 NTU. From the results on the bases of examination through SEM, flux, turbidity and SDI, it was clear that membrane performance could be enhanced by coagulation in the aspect of both water quantity and quality. Especially, coagulation pretreatment was found to have more significant impact on the membrane performance for MF, resulting to a drastic enhancement of flux and permeate quality. Although optimum operating conditions depend on the feed water quality, it can be suggested that membrane filtration using MF and UF can be a promising pretreatment technology for RO feed in seawater desalination processes.