Inline coagulation–ultrafiltration as the pretreatment for reverse osmosis brine treatment and recovery

Abstract

To help resolve issues associated with reverse osmosis (RO) brine handling for inland water reuse plants, RO brine treatment and recovery from NEWater factory was demonstrated in a laboratory using a low cost, less footprint and low energy consumption pretreatment method of inline coagulation–ultrafiltration (UF). Polyaluminum chloride (PACl), aluminum chlorohydrate (ACH) and ferric chloride (FeCl3) were chosen as the coagulants. PACl and ACH attained dissolved organic carbon (DOC) removal of 31% and 27% respectively at the optimal dosage (0.556mM as Al), while FeCl3 outperformed PACl and ACH at this molar dosage, reaching up to 60% of DOC removal. At the optimal pH (pH7), FeCl3 was again more superior with the highest DOC removal efficiency of 55%. FeCl3 also presented the highest phosphate (>99%) and silica removals (14%) at its optimum dosage and pH. Liquid chromatography-organic carbon detector (LC-OCD) and fluorescence excitation–emission matrix (EEM) were used to characterize the DOC fractions removed by inline coagulation-UF. For LC-OCD, FeCl3 revealed higher removal efficiency for almost all the DOC fractions ranging from low to high molecular weight. These results suggest that the inline-coagulation (FeCl3)-UF pretreatment is potential in reducing the fouling tendency of downstream RO because of its high DOC and phosphate removal efficiency.