Pretreatment for seawater desalination by flocculation: Performance of modified poly ferric silicate (PFSi-δ) and ferric chloride as flocculants

Abstract

Submerged microfiltration system coupled with in-line flocculation as pretreatment for seawater reverse osmosis has the potential to remove organic compounds and mitigate fouling. The effect of flocculation on the performance of microfiltration (MF) was investigated using two flocculants, namely, modified poly ferric silicate (PFSi-δ) and ferric chloride (FeCl 3). The experimental results were analysed in terms of organic removal efficiency and critical flux. Both PFSi-δ and FeCl 3 were found to be suitable as pretreatment because of their capacity in removing organic compounds. The results show that PFSi-δ was better than FeCl 3 in terms of removing turbidity and dissolved organic carbon (DOC), particularly in removing hydrophilic compounds. The highest DOC removals of 68% and 57% were obtained when PFSi-δ at a dose of 1.2 mg Fe 3+/L and FeCl 3 at 3 mg Fe 3+/L were used, respectively. It was observed that PFSi-δ (1.2 mg Fe 3+/L) and FeCl 3 (3 mg Fe 3+/L) led to an increase of critical flux from 20 L/m 2 h to 35 L/m 2 h and 55 L/m 2 h, respectively.