Using UV Spectroscopy and Molecular Weight Determinations to Investigate the Effect of Various Water Treatment Processes on NOM Removal: Australian Case Study
Natural organic material (NOM) has been the focus of many studies because of its ability to compromise water treatment processes. This case study utilized ultraviolet (UV) spectroscopy and molecular weight distributions to investigate the impact of six water treatment processes (alum coagulation, magnetic ion exchange (MIEX) resin treatment, chlorination, ozonation, powdered activated carbon (PAC) adsorption, and biological sand filtration) on the removal of NOM from an Australia water source, Myponga Reservoir. Each of these processes displayed different effects on the concentration and character of NOM. The removal of dissolved organic carbon (DOC) and UV absorbance at 254 nm (UV254) by MIEX and the biological sand filter was shown to follow first-order kinetics with rate constants ranging from 9.0×10−8 s−1 (biological sand filter) to 6.3×10−5 s−1 (MIEX treatment). UV spectroscopic investigations showed the potential to predict the formation of disinfection by-products from chlorination with strong correlations (R2 of 0.96) observed between the formation of trihalomethanes and the differential UV absorbance at 265 nm. Ozonation and biological sand filtration also appeared to target NOM absorbing at 265 nm. Molecular weight distribution analyses showed MIEX treatment to be the most effective single process in achieving high removals of a wide molecular weight range of NOM, consistent with the high removals of DOC and UV254 (up to 90% and 80% removal, respectively). The combination of alum and PAC, treatment options which exist at the majority of Australian water treatment plants, also proved effective for high NOM removal over a wide range of molecular weights, where alum effectively removed high molecular weight compounds, and PAC effectively removed low molecular weight compounds. This study has demonstrated that valuable information can be gained through simple manipulation of UV absorbance and molecular weight distribution data, which could be beneficial to water utilities in not only facilitating the selection of treatment processes when commissioning WTPs, but also optimizing existing treatment processes for effective NOM removal.
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