Factors affecting the removal of bromate and bromide in water by nanofiltration

Bromide is universal in surface water influenced by salt tide and brackish water. It is harmless to human until transferring to bromate (a kind of disinfection byproducts) under certain conditions such as oxidation. Though both of them are not easily removed by conventional water treatment, nanofiltration seems to be an efficient way to solve the problems. In this study, the removal of bromate and bromide by nanofiltration membranes were systematically investigated, considering the system pressure (0.2-0.3-0.4 MPa), pH (5-7-9), ionic strength (0.005-0.05-0.1 mM), membrane type (NF270 and NF90), and the influences of organic matters (humic acid and sodium alginate). The membrane flux and the removal efficiency of anions were taken into consideration. According to the results, the membrane flux increased along with the system pressure, but slight influence on the removal of bromate and bromide was observed. Rising pH and ionic strength could not obviously deteriorate the flux. However, the removal of these anions was enhanced by increasing pH as well as decreasing ionic strength. Compared with humic acid, severer flux decline and deterioration of anion removal were achieved when sodium alginate was added in feed solution. Regardless of the operating conditions, bromate was more easily removed by nanofiltration membranes than bromide, which could result from different steric hindrance. Compared with NF270, NF90 can reject bromide and bromate more efficiently. The findings in the present study would contribute to the deep understanding of the factors affecting removal of bromate and bromide by nanofiltration and provides guidance about application of it.