This work examined the role of manganese oxide (MnOx) in the formation of disinfection byproducts (DBPs) during Mn(II) removal by adsorption and catalytic oxidation by free chlorine (Cl2), in drinking water treatment. DBPs are of increasing concern as more is being learned about their carcinogenicity and genotoxicity. Results of column studies showed that exposure to MnOx-coated granular filter media did not increase DBP formation. Measured instantaneous DBP concentrations were higher when Cl2 was applied ahead of the column as compared to after the column. However, measured DBP concentrations when all samples were held for 24 hours were similar. Influent and effluent TTHM and HAA5 concentrations at two full scale plants were also examined – Putnam which removes Mn(II) across a dual media filter, and Lantern Hill (LH) which removes Mn(II) across second stage contactors (SSC). Putnam influent instantaneous HAAs and TTHMs were approximately 40% of 24-hour influent concentrations, while effluent HAAs and TTHMs were approximately 75% of 24-hour effluent concentrations. This indicates that a large fraction of the measured DBPs formed within the 15 minutes from filter influent to effluent. LH influent instantaneous HAAs and TTHMs were approximately 40% of 24-hour influent concentrations, while effluent HAAs and TTHMs were approximately 49% of 24-hour effluent concentrations (approximately 2 minutes form influent to effluent). These results confirm that the MnOx-coated SSC media, with much less media associated natural organic matter than a dual media filter for particle removal, showed even less of an impact on DBP formation, consistent with column experimental results. The presence of MnOx or MnOx coated surfaces does not appear to increase DBP formation due to the reactions between NOM and free chlorine. For water treatment plants applying pre-filter chlorine for Mn(II) catalytic oxidation across MnOx-coated granular media this means that resulting increases in filter effluent DBP concentrations as compared to application of free chlorine after media filtration are mainly functions of media associated NOM (along with time, pH, temperature etc.), not the MnOx surfaces. If DBP concentrations are unacceptably high and pre-filter chlorination is undesirable, an alternative method for Mn(II) removal should be considered.

Impact of manganese oxide-coated granular filter media on disinfection byproduct formation

256th National Meeting (2018)

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