Effect of ozone on microfiltration as a pretreatment of seawater reverse osmosis

The main purpose of this study is to evaluate a combined ozone and microfiltration (MF) membrane process as pre-treatment of a seawater reverse osmosis (SWRO) system. During the filtration of seawater (SW) with the MF membranes, membrane fouling on both hydrophilic (PHI) and hydrophobic (PHO) MF membranes (PVDF, 0.22 µm pore size) was investigated by measuring the variation of flux. A significant decline of flux was observed in both PHI and PHO membranes, showing much higher fouling in the PHO membrane than the PHI membrane, with and without pre-filtration. Ozonation of the SW was performed to investigate the effect of ozone on fouling of the MF membrane. Reduction of membrane fouling by ozone occurred in only the PHO membrane. In the case of the PHI membrane, pre-ozonation of the SW led to more severe fouling during filtration than was the case for non-ozonated SW.

In this work a combined ozone and MF membrane process as a pre-treatment in a SWRO system was tested, with a focus on investigating the effect of ozone on the reduction of fouling in the MF membrane. During the MF process of SW, a significant decline of flux was observed in both PHI and PHO membranes, showing much higher fouling in the PHO membrane than in the PHI membrane, with and without pre-filtration. The ozonation of SW prior to the membrane filtration affected both PHI and PHO membranes, but a distinct difference was observed. In the PHI membrane, the fouling was more severe due to the ozonation of the SW, producing an increase of Rc, which is the resistance caused by the cake layer. The formation of cake-causing matter by ozonation of SW could be attributed to the improvement in calcium complexation by ozone, leading to the conversion of dissolved organic matter into colloidal particles. In the PHO membrane, fouling was greatly reduced by pre-ozonation of the SW, showing a significant reduction in Rf, which is caused by pore plugging or adsorption in membrane pores. Production of TRO and changes of organics in their properties (such as increase of hydrophilicity and ionization, and decrease of molecular size) could be the reason for fouling reduction due to pre-ozonation of the SW.