Hybrid coagulation–nanofiltration membrane for removal of bromate and humic acid in water

Bromate is suspected to be a carcinogenic compound with a maximum contaminant level in drinking water imposed by the USEPA at 0.010 mg/L. The removal of bromide and bromate anions by hybrid coagulation–nanofiltration technique was systematically investigated in this study where humic acid (HA) was used as the model NOM. Two types of membranes (NF-270 and NF-90) and two types of coagulants (alum and ferrous sulphate) were investigated with regard to humic acid, bromide and bromate removals as well as the permeate flux decline and quality. It was found that bromide could not be effectively removed by nanofiltration, coagulation, or hybrid coagulation–nanofiltration, whereas bromate was reduced to bromide when ferrous sulphate was used. In addition to reducing bromate, humic acid was effectively removed by this technique while the permeate flux was maintained and in some cases improved, which suggests that the technique has some potentials to be applied in drinking water treatment train. Since coagulation and membrane filtration have been widely applied in drinking water treatment, the experimental results of this study indicate that the high removal rate of bromate in current water treatment processes can be achieved by simple modification of treatment processes and selection of proper coagulant.

Research highlights▶ Hybrid coagulation–nanofiltration could effectively remove humic acid and reduce bromate to bromate, while improving the permeate flux. ▶ Removal of bromide prior to bromate is not feasible compared to removing bromate after it is being formed. ▶ Hybrid coagulation–nanofiltration using ferrous sulphate coagulant and NF-90 membranes did not increase Rd/Rm ratio as much as that with NF-270 membranes. ▶ Types of membrane and coagulant influence efficiency of hybrid coagulation–nanofiltration.