Date of Award
8-2017
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Environmental Engineering and Earth Sciences
Committee Member
Dr. Tanju Karanfil, Committee Chair
Committee Member
Dr. Cindy Lee
Committee Member
Dr. David Ladner
Committee Member
Dr. Brian Powell
Abstract
Drinking water utilities are relying more than ever on water sources impacted by wastewater effluents. Disinfection of these waters during water treatment may lead to the formation of several disinfection by-products, including the probable human carcinogen N-nitrosodimethylamine (NDMA) and the regulated trihalomethanes (THMs). The main objectives of this dissertation work were to investigate i) the potential of ion exchange resins to remove simultaneously both NDMA and THMs, ii) the factors (i.e., pH and competing ions) that may influence the capability of ion exchange resins, and iii) the effect of bromide on the formation of NDMA. Two ion exchange resins were examined, a cation exchange resin (Plus) to target NDMA precursors and an anion exchange resin (MIEX) for THMs precursors control. The resins were applied individually and combined in the treatment of surface and wastewater effluent samples. The treatment with both resins removed simultaneously NDMA (43 - 85%) and THMs (39 - 65%) precursors. These results proved that the combined application of a cation and an anion exchange resins is a feasible treatment technique to control effectively NDMA and THMs precursors concomitantly since there were no interactions between the resins. The treatment of fresh and naturally attenuated samples containing varying wastewater content showed that neither the wastewater content nor the attenuation of the precursor affected the removals of NDMA and THMs precursors with the ion exchange resins. The hypothesis that the majority of NDMA precursors are amine - based compounds was tested by treating waters at different pH (5, 7 and 10). The speciation of NDMA precursors was expected to change as a function of pH and generally, amines have pKa values > 8. At a pH below their pKa values, NDMA precursors would be ionized (positively charged). The results of the treatment with the cation exchange resins validated the hypothesis as the majority of NDMA precursors were removed at pH 5 and 7 but not at pH10. Additionally, basic conditions (pH 10) also promoted the release of NDMA precursors from the cation exchange resin. Wastewater effluent samples with naturally occurring levels of inorganic ions (e.g., bicarbonate, bromide, calcium, nitrate and sulfate) were enhanced to simulate a challenging treatment scenario. The results showed that the presence of high concentrations of calcium promoted the release of NDMA precursors in the cation exchange resin. The release of NDMA increased as calcium concentration increased. Nonetheless, NDMA precursors levels subsided after several regeneration cycles. In these challenging conditions, bromide was not removed in either the ambient or the amended wastewater effluent sample. Given that bromide is not well removed, its presence in water is a cause of concern because it can lead to the formation of brominated DBPs that are more cytotoxic and genotoxic than the chlorinated analogs. In this study bromide (0 - 1000 μg/L) increased the formation of NDMA only in aqueous solutions of NDMA model precursor compounds but not in surface waters. A different trend was observed in chloraminated wastewater effluent samples in which bromide suppressed the formation of NDMA with increasing bromide concentration. It is likely that bromochloramine preferentially reacted with background natural organic matter (NOM) instead of NDMA precursors thus decreasing the formation of NDMA. More NDMA was formed at pH 8 compared to pH 6. However, bromide increased the formation of NDMA in waters containing dimethylamine (DMA), trimethylamine (TMA) and poly(diallyldimethylammonium chloride) (polyDADMAC) and dissolved organic carbon (DOC) levels around 2 mg/L.
Recommended Citation
Sandi, Wilson Beita, "A Mixed Cation and Anion Exchange Resin System for the Simultaneous Removal of N-Nitrosodimethylamine and Trihalomethanes Precursors from Water" (2017). All Dissertations. 1970.
https://tigerprints.clemson.edu/all_dissertations/1970