Membranes for the control of natural organic matter from surface waters

A range of nanofiltration (NF) modules was evaluated to determine rejection of disinfection by-product (DBP) precursors from low turbidity surface waters. Dissolved organic carbon (DOC), trihalomethane formation potential (THMFP), haloacetic acid formation potential (HAAFP), and chloral hydrate formation potential (CHFP) rejections averaged 90, 97, 94, and 86%, respectively. Rejections of bromide ion, an inorganic precursor, ranged from 40–80%. Pretreatment using microfiltration (MF) alone before NF provided some removal of turbidity but not enough to maintain the initial flux and recovery of the NF unit. NF runs were sustained over 30 days; however, some adverse changes in operational conditions were observed, and significant pressure increases were necessary to maintain flux. Precursor rejections by NF following MF varied little over time frames of up to 30 days. MF was only moderately effective in particle removals, with virtually no DBP precursor removal provided by MF. Ultrafiltration (UF) alone did not exhibit significant changes in operational conditions over a 30-day time frame; however, only modest precursor (<30% DOC) removal was observed.