Effects of water matrices on the degradation of naproxen by reactive radicals in the UV/peracetic acid process.

The UV/peracetic acid (UV/PAA) process as a novel advanced oxidation process has been reported to produce carbon-centered radicals (RC•) for Naproxen (NAP) degradation, which is a representative of naphthyl structure substances. Real water matrices, such as carbonate and bicarbonate ions (CO32-/HCO3-), humic acid (HA), and chloride ion (Cl-), may react with these reactive radicals and change their contributions to NAP degradation. The results showed that RC• contributed 60.8% and •OH contributed 39.2% to NAP degradation in pure water by a competition method. CO32-/HCO3- (0-20 mM) showed minimal effect on NAP degradation in the UV/PAA process, meanwhile, it has observable inhibition effect on NAP degradation in the UV/H2O2 process (mainly of •OH) and minimal effect in the UV/PAA process with tert-butanol (TBA) (mainly of RC•). Results suggested that CO32-/HCO3- could react with •OH yielding CO3•- with low reactivity to NAP, CO3•- could further react with PAA to produce RC•. This speculation was confirmed by the increased contribution of RC• to NAP degradation with the increase of CO32-/HCO3- concentration through the competition method. HA (0-5 mg/L) had a higher scavenging capacity for RC• than •OH because HA with naphthyl structure was likely to be attacked by RC•. Cl- (0-200 mM) had little effect on NAP degradation in the UV/PAA and UV/H2O2 processes, while exerted an observable inhibition on NAP degradation in the UV/PAA process with TBA. This finding suggested that Cl- could react with RC• to produce Cl•, which could further convert into HOCl•-, and then excess •OH was formed. The new knowledge on the conversion of reactive radicals obtained in this study provides an important basis for facilitating further research on the UV/PAA advanced oxidation.

UV/Peracetic Acid for Degradation of Pharmaceuticals and Reactive Species Evaluation.

Peracetic acid (PAA) is a widely used disinfectant, and combined UV light with PAA (i.e., UV/PAA) can be a novel advanced oxidation process for elimination of water contaminants. This study is among the first to evaluate the photolysis of PAA under UV irradiation (254 nm) and degradation of pharmaceuticals by UV/PAA. PAA exhibited high quantum yields (Φ254 nm = 1.20 and 2.09 mol·Einstein-1 for the neutral (PAA0) and anionic (PAA-) species, respectively) and also showed scavenging effects on hydroxyl radicals (k•OH/PAA0 = (9.33 ± 0.3) × 108 M-1·s-1 and k•OH/PAA- = (9.97 ± 2.3) × 109 M-1·s-1). The pharmaceuticals were persistent with PAA alone but degraded rapidly by UV/PAA. The contributions of direct photolysis, hydroxyl radicals, and other radicals to pharmaceutical degradation under UV/PAA were systematically evaluated. Results revealed that •OH was the primary radical responsible for the degradation of carbamazepine and ibuprofen by UV/PAA, whereas CH3C(═O)O• and/or CH3C(═O)O2• contributed significantly to the degradation of naproxen and 2-naphthoxyacetic acid by UV/PAA in addition to •OH. The carbon-centered radicals generated from UV/PAA showed strong reactivity to oxidize certain naphthyl compounds. The new knowledge obtained in this study will facilitate further research and development of UV/PAA as a new degradation strategy for water contaminants.

Oxidation of ß-lactam antibiotics by peracetic acid: Reaction kinetics, product and pathway evaluation.

Peracetic acid (PAA) is a disinfection oxidant used in many industries including wastewater treatment. ß-Lactams, a group of widely prescribed antibiotics, are frequently detected in wastewater effluents and surface waters. The reaction kinetics and transformation of seven ß-lactams (cefalexin (CFX), cefadroxil (CFR), cefapirin (CFP), cephalothin (CFT), ampicillin (AMP), amoxicillin (AMX) and penicillin G (PG)) toward PAA were investigated to elucidate the behavior of ß-lactams during PAA oxidation processes. The reaction follows second-order kinetics and is much faster at pH 5 and 7 than at pH 9 due to speciation of PAA. Reactivity to PAA follows the order of CFR âˆ¼ CFX > AMP âˆ¼ AMX > CFT âˆ¼ CFP âˆ¼ PG and is related to ß-lactam's nucleophilicity. The thioether sulfur of ß-lactams is attacked by PAA to generate sulfoxide products. Presence of the phenylglycinyl amino group on ß-lactams can significantly influence electron distribution and the highest occupied molecular orbital (HOMO) location and energy in ways that enhance the reactivity to PAA. Reaction rate constants obtained in clean water matrix can be used to accurately model the decay of ß-lactams by PAA in surface water matrix and only slightly overestimate the decay in wastewater matrix. Results of this study indicate that the oxidative transformation of ß-lactams by PAA can be expected under appropriate wastewater treatment conditions.

Transformation of aminopyrine in the presence of free available chlorine: Kinetics, products, and reaction pathways.

Aminopyrine (AMP) has been frequently detected in the aquatic environment. In this study, the transformation mechanism of AMP by free available chlorine (FAC) oxidation was investigated. The results showed that FAC reacted with AMP rapidly, and a 74% elimination was achieved for 1.30 µM AMP after 2 min at 14.08 µM FAC dose. AMP chlorination was strongly pH-dependent, and its reaction included second- and third-order kinetic processes. Three active FAC species, including chlorine monoxide (Cl2O), molecular chlorine (Cl2), and hypochlorous acid (HOCl), were observed to contribute to AMP degradation. The intrinsic rate constants of each FAC species with neutral (AMP0) and cation (AMP+) species were obtained by kinetic fitting. Cl2O exhibited the highest reactivity with AMP0 (kAMP0, Cl2O = (4.33 ± 1.4) × 109 M-1s-1). In addition, Cl2 showed high reactivity (106-107 M-1s-1) in the presence of chloride, compared with HOCl (kAMP+, HOCl = (5.73 ± 0.23) × 102 M-1s-1, kAMP0, HOCl = (9.68 ± 0.96) × 102 M-1s-1). At pH 6.15 and 14.08 µM FAC dose without chloride addition, the contribution of Cl2O reached to the maximum (33.3%), but in the whole pH range, HOCl was the main contributor (>66.6%) for AMP degradation. The significance of Cl2 was noticeable in water containing chloride. Moreover, 11 transformation products were identified, and the main transformation pathways included pyrazole ring breakage, hydroxylation, dehydrogenation, and halogenation.

Determination of selected pharmaceuticals in tap water and drinking water treatment plant by high-performance liquid chromatography-triple quadrupole mass spectrometer in Beijing, China.

A simultaneous determination method of 14 multi-class pharmaceuticals using solid-phase extraction (SPE) followed by high-performance liquid chromatography-tandem mass spectrometer (HPLC-MS/MS) was established to measure the occurrence and distribution of these pharmaceuticals in tap water and a drinking water treatment plant (DWTP) in Beijing, China. Target compounds included seven anti-inflammatory drugs, two antibacterial drugs, two lipid regulation drugs, one antiepileptic drug, and one hormone. Limits of detection (LODs) and limits of quantitation (LOQs) ranged from 0.01 to 1.80 ng/L and 0.05 to 3.00 ng/L, respectively. Intraday and inter-day precisions, recoveries of different matrices, and matrix effects were also investigated. Of the 14 pharmaceutical compounds selected, nine were identified in tap water of Beijing downtown with the concentration up to 38.24 ng/L (carbamazepine), and the concentration levels of detected pharmaceuticals in tap water (<5 ng/L for most pharmaceuticals) were lower than previous studies in other countries. In addition, ten and six pharmaceuticals were measured in raw water and finished water at the concentration ranged from 0.10 to 16.23 and 0.13 to 17.17 ng/L, respectively. Five compounds were detected most frequently in DWTP, namely antipyrine, carbamazepine, isopropylantipyrine, aminopyrine, and bezafibrate. Ibuprofen was found to be the highest concentration pharmaceutical during DWTP, up to 53.30 ng/L. DWTP shows a positive effect on the removal of most pharmaceuticals with 81.2-99.5 % removal efficiencies, followed by carbamazepine with 55.4 % removal efficiency, but it has no effect for removing ibuprofen and bezafibrate.

Influencing factors and degradation products of antipyrine chlorination in water with free chlorine.

Owing to its low cost, free chlorine is one of the most common disinfectants for wastewater and drinking water treatment. However, the formation of disinfection byproducts has been found to occur after free chlorine disinfection in recent decades. Antipyrine (ANT), an anti-inflammatory analgesic, has been frequently detected in the aquatic environment. In this work, the removal efficiency of ANT by free chlorine oxidation in ultrapure water was investigated with batch experiments. The influencing factors on the removal of ANT were explored at initial concentrations of ANT from 0.04 to 0.64 mg/L, free chlorine dosage from 0.30 to 1.31 mg/L, and pH from 1.5 to 9.0. The main degradation products were identified by solid phase extraction-gas chromatography-mass spectrometry. The results showed that ANT reacted rapidly with free chlorine in ultrapure water systems and up to 90.6% removal efficiency of ANT was achieved after 25 sec (initial free chlorine 1 mg/L, ANT 0.5 mg/L, pH 7.0). Higher oxidant dosage, lower ANT initial concentration and low pH favor the ANT removal. The main degradation product in ANT chlorination was a monochlorine substitution product (4-chloro-1,2-dihydro-1,5-dimethyl-2-phenyl-3H-pyrazol-3-one), which can be further chlorinated by free chlorine. In addition, the total organic carbon result indicated that ANT is difficult to be mineralized using chlorine.

Reaction kinetics and transformation of antipyrine chlorination with free chlorine.

Chlorine has been documented that it can effectively remove some pharmaceuticals. Recently, new active oxidants chlorine monoxide and molecular chlorine, which exist as free active chlorine in solution, were reported during pharmaceuticals chlorination. In this study, reaction kinetics, active oxidants, and transformation products during antipyrine chlorination were investigated with batch experiments. The reaction orders in [chlorine] were determined at various pH (6.53-7.62) and ranged from 1.13 ± 0.15 to 1.59 ± 0.08, which indicated that antipyrine chlorination is the concurrent existence of reactions appearing first-order and second-order in [chlorine]. The results by varying solution conditions (solution pH, chloride, ionic strength, and buffer concentration) show that chlorine monoxide and molecular chlorine play significant roles during the process of antipyrine chlorination. With kinetics modeling, the second-order rate constants for hypochlorous acid, chlorine monoxide, and molecular chlorine were obtained at 25 ± 2 °C (units: M(-1) s(-1)): kHOCl = 3.23 × 10(3), kCL2 = 2.86 × 10(7), kCL2O= 8.38 × 10(9) (R(2) = 0.9801). At pH 7, hypochlorous acid and chlorine monoxide are the main contributors to the degradation of antipyrine, about 80% and 20%, respectively (calculated by kHOCl, kCL2 and kCL2O. By applying these rate constants to predict the antipyrine elimination in real water matrixes (surface water, ground water), a good agreement was obtained, particularly in ground water. Moreover, liquid chromatography-tandems mass spectrometry (LC-MS/MS) and gas chromatograph-mass spectrometry (GC-MS) were used for products identification. Two main intermediate products and three stable products were observed during the process of antipyrine chlorination. The possible routes for antipyrine chlorination were proposed, which mainly consisted of halogenations, dealkylations and hydroxylations.