Influence of bromide on low-pressure membrane filtration for controlling DBPs in surface waters

The removal of disinfection by-product (DBP) precursors by low pressure membrane filtration was investigated on 3 surface waters. One ultrafiltration (UF) membrane of molecular weight cutoff (MWCO) 100,000 daltons and 4 nanofiltration (NF) membranes with MWCO of 200-800 daltons were evaluated in pilot plants. Configurations were spiral wound and hollow fibre; combinations investigated were NF and UF alone, and UF as a pre-treatment to NF. Simulated distribution system (SDS) trihalomethane (THM) and SDSDBP tests were carried out by chlorinating samples, and measuring THM and other compounds after various time intervals. Purge-and-trap or extraction procedures were used to concentrate the compounds. The removal of inorganic and organic compounds was also monitored. Waters containing natural and enhanced concentrations of bromide were studied. DBP formation was little affected by UF. When little or no bromide was present in the permeate, hollow fibre NF membranes with MWCO of 400-800 daltons controlled DPB formation. Higher bromoform levels arose from the chlorination of permeates of waters with elevated bromide concentrations. Spiral wound NF membranes of 200-300 daltons controlled the formation of brominated THM if pre-treatment was undertaken. There are 51 references.