Browsing by Author "Mitch, William A."

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Novel Chlorination Byproducts of Tryptophan: Initial High-Yield Transformation Products versus Small Molecule Disinfection Byproducts
(2020-03-01)
Hua, Lap-Cuong
;
Kim, Euna
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McCurry, Daniel L.
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Huang, Chihpin
;
Mitch, William A.
Because of the difficulty of carbon-carbon bond cleavage needed to liberate the small molecule chlorine disinfection byproducts (DBPs; e.g., trihalomethanes), they typically form at <1% yields. By using N-acetyl-tryptophan (NacTrp) as a model reactive peptide-bound monomer within natural organic matter (NOM), this study illustrates the characterization of its initial chlorine transformation products as an alternative approach to identify high-yield DBPs. When NacTrp was treated at 1-10 chlorine/NacTrp molar ratios, seven novel initial transformation products were purified and characterized by high-resolution mass spectrometry, including two chlorine-containing DBPs. The total concentrations of these novel DBPs accounted for 55-100% conversion of the parent NacTrp at 1-5 chlorine/NacTrp molar ratios over 24 h, compared to <= 5% for the total concentrations of small molecule DBPs. At a 10:1 molar ratio, the novel DBP concentrations declined over 24 h to account for 25% molar conversion, while small molecule DBP concentrations increased, yet still accounted for only 20% molar conversion. A reaction pathway consistent with these initial transformation products was proposed. The high yields of these novel DBPs are attributable to the lack of carbon-carbon bond cleavage. This study illustrates the identification of initial transformation products of important monomers as an efficient option to characterize the unknown DBPs.
Pilot-scale evaluation of oxidant speciation, 1,4-dioxane degradation and disinfection byproduct formation during UV/hydrogen peroxide, UV/free chlorine and UV/chloramines advanced oxidation process treatment for potable reuse
(2019-11-01)
Zhang, Zhong
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Chuang, Yi-Hsueh
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Szczuka, Aleksandra
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Ishida, Kenneth P.
;
Roback, Shannon
Advanced oxidation using UV/free chlorine and UV/chloramines are being considered as alternatives to UV/H2O2 for treatment of reverse osmosis (RO) permeate in treatment trains for the potable reuse of municipal wastewater. This pilot-scale comparison of the three advanced oxidation processes (AOPs) evaluated three factors important for selecting among these alternatives. First, the study characterized the speciation of oxidants serving as the source of radicals within the AOPs to facilitate process modeling. Kinetic modeling that included consideration of the chloramines occurring in RO permeate accurately predicted oxidant speciation. Modeling of the UV/free chlorine AOP indicated that free chlorine is scavenged by reactions with ammonia and monochloramine in RO permeate, such that oxidant speciation can shift in favor of dichloramine over the short (similar to 30 s) timescale of AOP treatment. Second, the order of efficacy for degrading the target contaminant, 1,4-dioxane, in terms of minimizing UV fluence was UV/free chlorine > UV/H2O2 >> UV/chloramines. However, estimates indicated that the UV/chloramines and UV/H2O2 AOPs could be similar on a cost-effectiveness basis due to savings in reagent costs by the UV/chloramines AOP, provided the RO permeate featured >3 mg/L as Cl-2 chloramines. Third, the study evaluated whether the use of chlorine-based oxidants within the UV/free chlorine and UV/chloramines AOPs enhanced disinfection byproduct (DBP) formation. Even after AOP treatment and chloramination, total halogenated DBP formation remained low at <15 mu g/L for all three AOPs. DBP formation was similar between the AOPs, except that the UV/free chlorine AOP promoted haloacetaldehyde formation, while the UV/H2O2 and UV/chloramines AOPs followed by chloramination increased chloropicrin formation. However, total DBP formation on a toxic potency-weighted basis was similar among the AOPs, since haloacetonitriles and haloacetamides were the dominant contributors and did not differ significantly among the AOPs. (C) 2019 Elsevier Ltd. All rights reserved.
Pilot-scale ozone/biological activated carbon treatment of reverse osmosis concentrate: potential for synergism between nitrate and contaminant removal and potable reuse
(2020-05-01)
Zhang, Zhong
;
King, Jacob F.
;
Szczuka, Aleksandra
;
Chuang, Yi-Hsueh
;
Mitch, William A.
With limited budgets, utilities may forego potable reuse of municipal wastewater to meet regulations requiring nitrate and contaminant removal from discharges. At 85% recovery, reverse osmosis (RO)-based potable reuse rejects contaminants into a concentrate flowrate that is 6.7-fold lower than wastewater discharges. This study evaluated the footprint and cost savings associated with treating nitrate and contaminants in RO concentrate vs. wastewater effluent. Pilot-scale ozone and biological activated carbon (BAC) treatment of RO concentrate provided design parameters needed for this comparison. Addition of 60 mg C per L methanol as a carbon source was needed to achieve complete denitrification of 70 mg N per L nitrate within a 30 min BAC empty bed contact time. Combined with pre-ozonation at 0.5 mg O-3/mg DOC, this treatment removed >74% of fipronil, imidacloprid, atenolol, DEET and sulfamethoxazole. Estimates indicated that applying ozone/BAC treatment to RO concentrate rather than conventional wastewater effluent for contaminant removal prior to discharge would offset 60% of the footprint and 25% of the cost required for the RO-based potable reuse train. Considering these savings, the reuse train cost could be recouped if the product water were sold at rates below those current in southern California. These results suggest synergy rather than competition between potable reuse and contaminant removal.