Recovery of sludge produced from Ti-salt flocculation as pretreatment to seawater reverse osmosis

Abstract

In this study, titanium tetrachloride (TiCl(4)), titanium sulfate (Ti(SO(4))(2)) and ferric chloride (FeCl(3)) flocculation as a pretreatment to seawater reverse osmosis (SWRO) were investigated. Their ability to remove turbidity, seawater organic matter (SWOM) and controlling the feed water quality of SWRO was evaluated. Flux decline of SWRO and membrane autopsy were studied. Titanium dioxide (TiO(2)) produced from sludge after Ti-salt flocculation was characterized in terms of particle structure and photocatalytic activity. A hybrid system of flocculation followed by granular activated carbon (GAC) filtration was employed to remove the suspended micro-flocs after different flocculations. The optimum dose of 10 mg/L TiCl(4) and FeCl(3) were used. The turbidity removal for the three coagulants was marginal at different doses at pH 6 and 8. Flocculation followed by GAC filtration significantly reduced the turbidity values from 1.5 NTU to about 0.35 NTU using TiCl(4) and 0.40 using FeCl(3). Silt density index (SDI(15)) was also decreased from 5.0 to 4.2 and 4.7, respectively. Removal of dissolved organic carbon (DOC), colour and UV absorbance after TiCl(4) and flocculation followed by GAC filtration was found to be effective and similar. TiO(2) produced from sludge showed very high photocatalytic activity under UV-irradiation. Acetaldehyde was completely removed after 45 min photocatalytic reaction