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Oxidation kinetics of iodide and HOI/OI- by permanganate were studied in the pH range of 5.0-10.0. Iodide oxidation and iodate formation were faster at lower pH. The apparent second-order rate constants (kobs) for iodide oxidation by permanganate decrease with increasing pH from 29 M-1 s-1 at pH 5.0 and 6.9 M-1 s-1 at pH 7.0 to 2.7 M-1 s-1 at pH 10.0. kobs for HOI abatement are 56 M-1 s-1 at pH 5.0, 2.5 M-1 s-1 at pH 7.0, and 173 M-1 s-1 at pH 10.0. Iodate yields over HOI abatement decrease from 98% at pH 6.0 to 33% for pH ≥ 9.5, demonstrating that HOI disproportionation dominates HOI transformation by permanganate at pH ≥ 8.0. MnO2 formed as a product from permanganate reduction, oxidizes HOI to iodate for pH < 8.0, and promotes HOI disproportionation for pH ≥ 8.0. The rate of HOI oxidation or disproportionation induced by MnO2 is much lower than for permanganate. During treatment of iodide-containing waters, the potential for iodinated disinfection byproducts (I-DBPs) formation is highest at pH 7.0-8.0 due to the long lifetime of HOI. For pH < 6.0, HOI/I2 is quickly oxidized by permanganate to iodate, whereas for pH ≥ 8.0, HOI/OI- undergoes a fast permanganate-mediated disproportionation. [ABSTRACT FROM AUTHOR]

It has been shown previously that the disproportionation of halogen-containing oxidants (e.g., HOCl, HOBr, and ClO2) is enhanced by a CuO-catalyzed process. In this study, the transformation of iodine during chlorination in the presence of CuO was investigated. There is no significant enhancement of the disproportionation of hypoiodous acid (HOI) in the presence of CuO. The formation rate of iodate (IO3-) in the CuO-HOCl-I- system significantly increased when compared to homogeneous solutions, which was ascribed to the activation of HOCl by CuO enhancing its reactivity toward HOI. In this reaction system, iodate formation rates increase with increasing CuO (0-0.5 g L-1) and bromide (0-2 μM) doses and with decreasing pH (9.6-6.6). Iodate does not adsorb to the CuO surfaces used in this study. Nevertheless, iodate concentrations decreased after a maximum was reached in the CuO-HOCl-I-(-Br-) systems. Similarly, the iodate concentrations decrease as a function of time in the CuO-HOCl-IO3- or CuO-HOBr-IO3- system, and the rates increase with decreasing pH (9.6-6.6) due to the enhanced reactivity of HOCl or HOBr in the presence of CuO. It could be demonstrated that iodate is oxidized to periodate by a CuO-activated hypohalous acid, which is adsorbed on the CuO surface. No periodate could be measured in filtered solutions because it was mainly adsorbed to CuO. The adsorbed periodate was identified by scanning electron microscopy plus energy dispersive spectroscopy and X-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

For real-time control of ozonation processes in water works, a sequencing batch reactor was constructed to measure the ozone decay rate constant (kO3) in short time intervals of about 15 min. The batch reactor is filled during the production process, immediately after dissolving ozone in water by a static mixer. On the basis of kO3and the initial ozone concentration ([O3]0), and the experimentally determined ratio of the concentrations of•OH radicals to ozone (Rct), the degradation of micropollutants in ozone reactors (modeled as Continuously Stirred Tank Reactors - CSTRs) were calculated for compounds with known reaction rate constants with ozone and•OH radicals. Calculated degradation of atrazine, iopromide, benzotriazole and acesulfame are in good agreement with measured data. For acesulfame the following rate constants were determined in this study at 20oC: reaction rate constant with ozone = 88 M−1s−1, reaction rate constant with•OH radical = 4.55 × 109M−1s−1. For the ozone reaction an activation energy of 35 kJ/mol was determined. Similarly to micropollutants, the relative inactivation of microorganisms (N/N0) can be calculated based on the inactivation rate constant for ozone and if applicable the lag phase. The pI-value (= −logN/N0) was introduced and implemented in the process management system to calculate online the log inactivation of reference microorganisms such asB. subtilisspores. The system was tested for variation of pH (6.5–8.5), DOC (1.2–4.2 mg/L) flowrate 3.2–12 m3/h and temperature (5.7–9oC). Furthermore, a given pI-value, e.g. 1 for a 1-log inactivation ofB. subtilisspores, can be set as control parameter in the process management system. The ozone gas flow is then adjusted until the set pI-value is reached. The process control concept was validated withB. subtilisspores. Generally, a good agreement was found between calculated and measured inactivation data. It was also demonstrated, that a constant ozone residual may lead to insufficient disinfection or overdosing of ozone. The new process control concept for ozonations based on onsite measurement of the ozone decay rate constant and the pI-value allows to assess disinfection and degradation processes quantitatively in real-time. [ABSTRACT FROM AUTHOR]

N,N-Dimethylsulfamide (DMS), a newly identified, ubiquitous degradation product of the fungicide tolylfluanide, has been shown to be a N-nitrosodimethylamine (NDMA) precursor during ozonation. In this study, batch ozonation experiments in ultrapure buffered water, surface water, and tap water were performed to determine the kinetics and elucidate the mechanism of NDMA formation from DMS. It was found that at circumneutral pH, DMS reacts slowly with ozone (k ≈ 20 M-1 s-1) and moderately with hydroxyl radicals (k = 1.5 × 109 M-1s-1). The reaction of DMS with these oxidants does not lead to NDMA. NDMA was only formed if bromide was present during ozonation of DMS-containing waters. Bromide is oxidized to hypobromous acid (HOBr) by ozone which then reacts with the primary amine of DMS to form a Br—DMS species. The rate limiting step of the formation of Br—DMS is the formation of HOBr. The reaction to form Br—DMS has an apparent second order rate constant at pH 8 of >3 × 104 M-1s-1. The Br—DMS is transformed by ozone to NDMA and nitrate (k ≥ 5000 M-1 s-1), with yields of 54% and 39%, respectively, based on the primary amine nitrogen of DMS. These reactions release bromide, making bromide a catalyst. NDMA is also formed during ozonation of DMS in the presence of hypochlorous acid (20-30% yield). The last step of NDMA formation is an intramolecular rearrangement with sulfur dioxide extrusion. On the basis of the mechanistic and kinetic information, it was possible to model NDMA formation in DMS-containing Lake Zurich water. [ABSTRACT FROM AUTHOR]

Ozonation of bromide-containing waters causes the formation of bromate which is considered to be potentially carcinogenic. An investigation in Switzerland on water works using ozone (85) has shown that the new drinking water standard of 10 µg/L for bromate is generally not exceeded. This is mainly due to the relatively small bromide concentrations which are typically below 25 µg/L. There is a characteristic relationship between bromate formation and the ozone exposure in a particular water type. This can be used to estimate the integral ozone exposure from the bromate formation which allows the assessment of the efficiency of the disinfection. This new concept is illustrated by means of two examples. [ABSTRACT FROM AUTHOR]

Oxidation kinetics of iodide and HOI/OI(-) by permanganate were studied in the pH range of 5.0-10.0. Iodide oxidation and iodate formation were faster at lower pH. The apparent second-order rate constants (k(obs)) for iodide oxidation by permanganate decrease with increasing pH from 29 M(-1) s(-1) at pH 5.0 and 6.9 M(-1) s(-1) at pH 7.0 to 2.7 M(-1) s(-1) at pH 10.0. k(obs) for HOI abatement are 56 M(-1) s(-1) at pH 5.0, 2.5 M(-1) s(-1) at pH 7.0, and 173 M(-1) s(-1) at pH 10.0. Iodate yields over HOI abatement decrease from 98% at pH 6.0 to 33% for pH ≥ 9.5, demonstrating that HOI disproportionation dominates HOI transformation by permanganate at pH ≥ 8.0. MnO2 formed as a product from permanganate reduction, oxidizes HOI to iodate for pH < 8.0, and promotes HOI disproportionation for pH ≥ 8.0. The rate of HOI oxidation or disproportionation induced by MnO2 is much lower than for permanganate. During treatment of iodide-containing waters, the potential for iodinated disinfection byproducts (I-DBPs) formation is highest at pH 7.0-8.0 due to the long lifetime of HOI. For pH < 6.0, HOI/I2 is quickly oxidized by permanganate to iodate, whereas for pH ≥ 8.0, HOI/OI(-) undergoes a fast permanganate-mediated disproportionation.

Peracetic acid (PAA) is a disinfectant considered for use in ballast water treatment, but its chemical behavior in such systems (i.e., saline waters) is largely unknown. In this study, the reactivity of PAA with halide ions (chloride and bromide) to form secondary oxidants (HOCl, HOBr) was investigated. For the PAA-chloride and PAA-bromide reactions, second-order rate constants of (1.47 ± 0.58) × 10(-5) and 0.24 ± 0.02 M(-1) s(-1) were determined for the formation of HOCl or HOBr, respectively. Hydrogen peroxide (H2O2), which is always present in PAA solutions, reduced HOCl or HOBr to chloride or bromide, respectively. As a consequence, in PAA-treated solutions with [H2O2] > [PAA], the HOBr (HOCl) steady-state concentrations were low with a limited formation of brominated (chlorinated) disinfection byproducts (DBPs). HOI (formed from the PAA-iodide reaction) affected this process because it can react with H2O2 back to iodide. H2O2 is thus consumed in a catalytic cycle and leads to less efficient HOBr scavenging at even low iodide concentrations (<1 μM). In PAA-treated solutions with [H2O2] < [PAA] and high bromide levels, mostly brominated DBPs are formed. In synthetic water, bromate was formed from the oxidation of bromide. In natural brackish waters, bromoform (CHBr3), bromoacetic acid (MBAA), dibromoacetic acid (DBAA), and tribromoacetic acid (TBAA) formed at up to 260, 106, 230, and 89 μg/L, respectively for doses of 2 mM (ca. 150 mg/L) PAA and [H2O2] < [PAA]. The same brackish waters, treated with PAA with [H2O2] ≫ [PAA], similar to conditions found in commercial PAA solutions, resulted in no trihalomethanes and only low haloacetic acid concentrations.

It has been shown previously that the disproportionation of halogen-containing oxidants (e.g., HOCl, HOBr, and ClO2) is enhanced by a CuO-catalyzed process. In this study, the transformation of iodine during chlorination in the presence of CuO was investigated. There is no significant enhancement of the disproportionation of hypoiodous acid (HOI) in the presence of CuO. The formation rate of iodate (IO3(-)) in the CuO-HOCl-I(-) system significantly increased when compared to homogeneous solutions, which was ascribed to the activation of HOCl by CuO enhancing its reactivity toward HOI. In this reaction system, iodate formation rates increase with increasing CuO (0-0.5 g L(-1)) and bromide (0-2 μM) doses and with decreasing pH (9.6-6.6). Iodate does not adsorb to the CuO surfaces used in this study. Nevertheless, iodate concentrations decreased after a maximum was reached in the CuO-HOCl-I(-)(-Br(-)) systems. Similarly, the iodate concentrations decrease as a function of time in the CuO-HOCl-IO3(-) or CuO-HOBr-IO3(-) system, and the rates increase with decreasing pH (9.6-6.6) due to the enhanced reactivity of HOCl or HOBr in the presence of CuO. It could be demonstrated that iodate is oxidized to periodate by a CuO-activated hypohalous acid, which is adsorbed on the CuO surface. No periodate could be measured in filtered solutions because it was mainly adsorbed to CuO. The adsorbed periodate was identified by scanning electron microscopy plus energy dispersive spectroscopy and X-ray photoelectron spectroscopy.

Ozonation is effective in improving the quality of municipal wastewater effluents by eliminating organic micropollutants. Nevertheless, ozone process design is still limited by (i) the large number of structurally diverse micropollutants and (ii) the varying quality of wastewater matrices (especially dissolved organic matter). These issues were addressed by grouping 16 micropollutants according to their ozone and hydroxyl radical ((•)OH) rate constants and normalizing the applied ozone dose to the dissolved organic carbon concentration (i.e., g O3/g DOC). Consistent elimination of micropollutants was observed in 10 secondary municipal wastewater effluents spiked with 16 micropollutants (∼2 μg/L) in the absence of ozone demand exerted by nitrite. The elimination of ozone-refractory micropollutants was well predicted by measuring the (•)OH exposure by the decrease of the probe compound p-chlorobenzoic acid. The average molar (•)OH yields (moles of (•)OH produced per mole of ozone consumed) were 21 ± 3% for g O3/g DOC = 1.0, and the average rate constant for the reaction of (•)OH with effluent organic matter was (2.1 ± 0.6) × 10(4) (mg C/L)(-1) s(-1). On the basis of these results, a DOC-normalized ozone dose, together with the rate constants for the reaction of the selected micropollutants with ozone and (•)OH, and the measurement of the (•)OH exposure are proposed as key parameters for the prediction of the elimination efficiency of micropollutants during ozonation of municipal wastewater effluents with varying water quality.