In this study, a commonly used ferric chloride was utilised as coagulant for removing organic compounds from seawater. More than 57% of dissolved organic carbon (DOC) was removed at optimum dosage of 3 mg Fe+3/L. The coagulation by FeCl3 at optimum dosage could remove a majority (95%) of hydrophobic compounds. The results from Liquid Chromatography – Organic Carbon Detector showed that only <0.02 mg/L of hydrophobic compounds was found after coagulation. In addition, the modified fouling index decreased considerably from 15,848 s/L2 with raw seawater to 3,025 s/L2 with seawater after coagulation. In-line coagulation coupled with submerged membrane system (ICSMS) was also trialled. It is observed that critical flux was increased from 20 L/m2·h in the conventional submerged membrane system to 55 L/m2 h in ICSMS. The ICSMS could remain the high DOC removal efficiency (more than 70%) at filtration rate of 20 L/m2 h when keeping the development of trans-membrane pressure was significant lower than that of conventional submerged membrane system.
Keywords: desalination, ferric chloride, in-line coagulation, organic matter, seawater