Ozonation, ultrafiltration, and biofiltration for the control of NOM and DBP in drinking water

Ozone is an effective disinfectant that can inactivate microorganisms and reduce the formation of disinfection by-products (DBPs). Ultrafiltration and nanofiltration membranes are also capable of removing DBP precursors and pathogens. However, natural organic matter (NOM), which is ubiquitous in surface water, can result in membrane fouling. A novelly designed ozonation/membrane system followed by biofiltration, which is expected to enhance ozone mass transfer and reduce membrane fouling, was used in this study. The effect of this system on the rate of ozone mass transfer, the transformation of the NOM in terms of the variation of UV-254, humic substances and non-humic substances, assimilable organic carbon (AOC), and biodegradable organic carbon (BDOC) was assessed. The effect of operational parameters on the control of DBPs and ozonation by-products was also investigated. Tubular ceramic membranes with a molecular weight cut-off of 15 kD were used in the system.; A mathematical model was developed and used to calculate the volumetric mass transfer coefficient of ozone for the bench-scale system. This model was successfully predicted the dissolved ozone concentration in the water tank. The effects of two different mixers, simple Y mixer (SYM) and high efficiency mixer (HEM), on the rate of ozone mass transfer were investigated. With HEM, greater values of ozone volumetric mass transfer coefficient were obtained at lower ozone doses.; Lake Lansing water was used to study the transformation of NOM. Water temperature, ozone gas flow rate, and ozone dose were controlled. The ozonation/membrane system removed 15–30% of the dissolved organic carbon (DOC). The removal efficiency increased to 69–88%, when followed by biofiltration. Concentrations of AOC and BDOC significantly increased after treatment using the ozonation/membrane system but were effectively removed by subsequent biofiltration. The UV-254 absorbance decreased by up to 85% and humic substances were converted to non-humic substances after treated by the ozonation/membrane system.; The formation of trihalomethanes (THMs) and haloacetic acids (HAAS) was effectively decreased by the system and by its subsequent biofiltration. Although the concentrations of aldehydes and ketoacids increased significantly after ozonation, these compounds were removed effectively by the subsequent biofiltration. The decrease of chlorine demand was limited when treatment consisted of only ozonation/membrane. With biofiltration, the chlorine demand of water decreased by 60–90%.; Correlations between AOC and ozonation by-products were also investigated. The sum of ozonation by-products (aldehydes + 2-butanone + ketoacids), the concentration of aldehydes, and the concentration of methyl glyoxal were well correlated with AOC and could be good surrogate parameters for the AOC measurement.