The effects of combined ozonation and filtration on disinfection by-product formation

The effects of combined ozonation and membrane filtration on the removal of the natural organic matter (NOM) and the formation of disinfection by-products (DBPs) were investigated. Ozonation/filtration resulted in a reduction of up to 50% in the dissolved organic carbon (DOC) concentration. Furthermore, humic substances were converted to non-humic substances, with changes in the humic and non-humic substance concentrations of up to −50% and +20%, respectively. Ozonation/filtration resulted in the formation of partially oxidized compounds from NOM that were less reactive with chlorine, decreasing the concentration of simulated distribution system total trihalomethanes (SDS TTHMs) and simulated distribution system halo acetic acids (SDS HAAs) by up to 80% and 65%, respectively. Reducing the molecular weight cut-off (MWCO) of the membranes resulted in reductions in the concentrations of SDS TTHMs and SDS HAAs. Using a membrane with a 5 kD MWCO, the minimum gaseous ozone concentration required to bring about effective NOM degradation and meet regulatory requirements for chlorinated DBPs was 2.5 g/m3.