Hybrid filtration method for pre-treatment of seawater reverse osmosis (SWRO)

Hybrid processes combining fibre filter with deep bed filtration process such as (i) fibre filter and sand filter, (ii) fibre filter and anthracite and (iii) fibre filter and dual media filter were investigated as pre- treatments to SWRO. Seawater was drawn from Chowder Bay, Sydney. The effect of different pretreatment hybrid systems was investigated in terms of silt density index (SDI10), modified fouling index (MFI), headloss across the filters and reduction in turbidity and dissolved organic carbon (DOC). The in-line flocculation in fibre filter improved the performance of the pretreatment hybrid system as measured by the MFI, SDI10, headloss, turbidity and DOC removal. The lowest SDI10 and MFIwere found with a fibre filter operated at a filtration velocity of 40 m/h followed by dual media filter operated at a filtration velocity of 5 m/h. The lowest headloss and turbidity was found with a fibre filter operated at a filtration velocity of 40 m/hr followed by anthracite operated at a filtration velocity of 5 m/h. This system also gave an effluent with the lowest DOC of 0.64 mg/L corresponding to a removal efficiency of about 70%.