Transformation By-products Research Articles

Solar light-induced degradation of ethyl paraben with CuOx/BiVO4: Statistical evaluation of operating factors and transformation by-products

In this work, the solar light-induced photocatalytic degradation of ethyl paraben (EP) was studied using CuOx/BiVO4 with 0.75wt.% copper loading, a relatively new photocatalyst that can exploit a large portion of the solar spectrum. The synthesized catalyst had a primary crystallite size of ca 37nm, a specific surface area of 1m2/g and a direct bandgap of 2.3eV. A factorial design methodology was implemented to evaluate the importance of EP concentration (500–1500μg/L), catalyst concentration (100–500mg/L), reaction time (10–60min), the presence of radical scavengers (pure water or 500mg/L bicarbonates) and initial solution pH (3–9) on EP removal. All individual effects were statistically significant and so was the second-order interaction of EP concentration with reaction time. Interestingly and differently from the majority of photocatalytic studies, the presence of bicarbonates promotes the photocatalytic degradation of ethyl paraben. The photocatalytic activity drops from 98% to 79% after five consecutive runs, possibly due to accumulation of oxidation by-products. Liquid chromatography-time of flight mass spectrometry (LC-TOF-MS) revealed that EP degradation occurs mainly via dealkylation followed by hydroxylation reactions and the formation of methyl paraben, 4-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid and 3,4-dihydroxybenzoic acid as primary transformation by-products.

Solar photocatalytic degradation of sulfamethoxazole over tungsten – Modified TiO2

Ten x% W-P25(T) composite catalysts were synthesized, characterized and tested for the photocatalytic degradation of antibiotic sulfamethoxazole (SMX), where x=1–6wt.% is the WO3 content and T=600–900°C is the calcination temperature applied for the preparation of catalysts. Modification of TiO2 with tungsten results in materials with higher anatase content and specific surface area, compared to undoped samples calcined at the same temperature, and in a small shift of the absorption threshold toward the visible region.Screening experiments showed that the 4% W-P25(700) catalyst was the most active for SMX degradation (350μg/L) under simulated solar irradiation enhancing the rate of pristine P25-TiO2 by 50%; this catalyst was used in subsequent kinetic and mechanistic experiments.The rate of degradation increases with increasing catalyst concentration in the range 10–250mg/L, while experiments at varying SMX concentration show a transition from first (at 200μg/L) to zeroth (at 1000μg/L) order kinetics. Degradation in actual matrices (wastewater and drinking water) is slower than in pure water due to the presence of non-target organics and anions; nonetheless, the presence of electron acceptors such as hydrogen peroxide or sodium persulfate enhances considerably degradation rates.SMX degradation proceeds through the formation of several primary and secondary transformation by-products (TBPs) as evidenced by LC-TOF-MS analysis. Based on the identified TBPs and their temporal evolution profiles, transformation pathways are proposed. The antimicrobial activity of SMX and its TBPs was tested against Escherichia coli and Enterococcus faecalis reference strains, showing that toxicity partially decreases upon oxidation.

Degradation of ethyl paraben by heat-activated persulfate oxidation: statistical evaluation of operating factors and transformation pathways.

A factorial design methodology was implemented to evaluate the importance of ethyl paraben (EP) concentration (500-1500μg/L), sodium persulfate concentration (400-500mg/L), temperature (40-60°C), reaction time (2-30min), water matrix (pure water or secondary treated wastewater), and initial solution pH (3-9) on EP removal by heat-activated persulfate oxidation. All individual effects, except the solution pH, were statistically significant and so were the second-order interactions of ethyl paraben concentration with temperature or the reaction time. The influence of the water matrix was crucial, and the efficiency of the process was lower in secondary treated wastewater due to the presence of natural organic matter and inorganic salts that compete with ethyl paraben for the reactive oxygen species. Liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) was employed to identify major transformation by-products (TBPs); 13 compounds were detected as TBPs of EP. Degradation occurred through (i) hydroxylation, (ii) dealkylation, and (iii) oligomerization reactions leading to TBPs with ether and biphenyl structures. Oligomerization reactions were found to be the dominant pathway during the first steps of the reaction. The toxicity of 500μg/L EP in secondary treated wastewater was tested against marine bacteria Vibrio fischeri; toxicity increased during the first minutes due to the production of several TBPs, but it consistently decreased thereafter.

Oxidation of bisphenol A in water by heat-activated persulfate

The heat-activated persulfate oxidation of bisphenol A (BPA), a representative endocrine disrupting compound, was investigated with respect to the effect of several process variables on degradation rates. The activation temperature appears to be the single most important parameter, i.e. a temperature increase from 40 to 70 °C results in an 80-fold rate increase. Regarding initial BPA concentration, the reaction follows a pseudo-first order rate expression, where the kinetic constant decreases from 11.5 10−2 to 3.5 10−2 min−1 when BPA concentration increases from 110 to 440 μg/L. Reactions in actual water matrices, such as bottled water and secondary treated wastewater, are slower than in pure water since various organic/inorganic water constituents compete with BPA for being oxidized by the reactive oxidizing species; this was confirmed with experiments in pure water spiked with humic acid or bicarbonate. Interestingly though, the presence of chloride seems to promote BPA degradation. Furthermore, degradation is favored at near-neutral pH and increased sodium persulfate (SPS) concentrations.Experiments at an increased BPA concentration of 20 mg/L were performed to identify transformation by-products (TBPs), as well as assess the mineralization and toxicity of the treated samples. Liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) revealed the formation of eleven TBPs of BPA and plausible pathways including hydroxylation, oxidation, cleavage and oligomerization reactions are proposed. Mineralization occurs slower than BPA degradation, while the toxicity to marine bacteria Vibrio fischeri increases during the early stages of the reaction but it progressively decreases thereafter.

Kinetic and mechanistic investigation of azathioprine degradation in water by UV, UV/H2O2 and UV/persulfate

This study investigated the removal of azathioprine (AZA), an immunosuppressant xenobiotic found in hospital effluent, using direct UV-254nm photolysis, UV/H2O2 and UV/persulfate (UV/PS). AZA cannot be effectively degraded by direct UV photolysis, while the photodegradation efficiency of AZA significantly increases with addition of H2O2 or PS, due to the generation of HO and SO4−, respectively. Compared with AZA removal of 10% by direct UV photolysis at UV dose of 510mJcm−2, UV/H2O2 and UV/PS can remove 68% and 87% of AZA, respectively, at an oxidant dose of 100μM. The second-order rate constants of AZA with HO and SO4− are 1.86×109M−1s−1 and 2.16×109M−1s−1, respectively. There is a proportional increase of AZA degradation efficiency with the increasing oxidant dose in the range of 10–100μM, beyond which radical scavenging effect can negate the radical generation process. The effects of water quality, including pH, NOM and inorganic anions, were also investigated. The removal efficiency of AZA in the UV/H2O2 and UV/PS processes constantly decreases with the increasing pH. NOM significantly reduces the degradation efficiency of AZA through radical scavenging and UV absorption. The inhibition of AZA photodegradation is also affected by the presence of inorganic anions, following the order of HCO3−>Cl−>NO3−≈SO42−. Real water samples of treated water from a water treatment plant and secondary effluent from a wastewater treatment plant were used for the assessment of the UV treatment performances. Various AZA transformation by-products were identified to investigate the degradation mechanism of AZA in the UV-AOP systems. The addition of 100μM oxidant significantly decreases the treatment cost from 0.844 (for UV photolysis) to 0.078 (for UV/H2O2) and 0.067US$m−3order−1 (for UV/PS), respectively, indicating that UV/PS is the most cost-effective process for AZA degradation.

Boron-doped diamond oxidation of amoxicillin pharmaceutical formulation: Statistical evaluation of operating parameters, reaction pathways and antibacterial activity

The electrochemical oxidation of a commercial amoxicillin formulation over a boron-doped diamond (BDD) anode was investigated. The effect of initial COD concentration (1–2 g/L), current density (30–50 mA/cm2), treatment time (15–90 min), initial pH (3–9) and electrolyte concentration (2–4 g/L NaCl) on COD removal was assessed through a factorial design methodology. For the range of conditions in question, the first three single effects, as well as the interaction between COD and time were the most important ones in terms of mass of COD removed.Liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) was employed to identify major transformation by-products (TBPs); thirteen compounds were detected as TBPs of AMX electrochemical degradation, while several others appear in the original formulation. AMX degradation occurs though the following pathways: (i) hydroxylation mainly in the benzoic ring, (ii) opening of β-lactam ring followed by decarboxylation, hydroxylation and re-arrangement, and (iii) bond cleavage between the carbons of amino and amide groups. Furthermore, the process is accompanied by the release of several ions, i.e. nitrate, sulfate and ammonium.The antibiotic activity of AMX up to 1000 mg/L was tested against Klebsiella pneumoniae and Enterococcus faecalis reference strains; both bacteria are completely inactivated at this concentration but the activity is reduced substantially at lower concentrations. Oxidized samples still exhibit some antibacterial activity (50–60%) which is due to TBPs and active chlorine species present in the liquid phase. The latter are generated from chloride ions and enhance considerably AMX degradation rates.

Photodegradation of ethyl paraben using simulated solar radiation and Ag3PO4 photocatalyst

In this work, the solar light-induced photocatalytic degradation of ethyl paraben (EP), a representative of the parabens family, was studied using silver orthophosphate, a relatively new photocatalytic material. The catalyst was synthesized by a precipitation method and had a primary crystallite size of ca 70nm, specific surface area of 1.4m2/g and a bandgap of 2.4eV. A factorial design methodology was implemented to evaluate the importance of EP concentration (500–1500μg/L), catalyst concentration (100–500mg/L), reaction time (4–30min), water matrix (pure water or 10mg/L humic acid) and initial solution pH (3–9) on EP removal. All individual effects but solution pH were statistically significant and so were the second-order interactions of EP concentration with reaction time or catalyst concentration. The water matrix effect was negative (all other effects were positive) signifying the role of humic acid as scavenger of the oxidant species. Liquid chromatography-time of flight mass spectrometry revealed the formation of methyl paraben, 4-hydroxybenzoic acid, benzoic acid and phenol as primary transformation by-products; these are formed through dealkylation and decarboxylation reactions initiated primarily by the photogenerated holes. Estrogenicity assays showed that methyl paraben was more estrogenic than EP; however, parabens are slightly estrogenic compared to 17β-estradiol.

Significant role of UV and carbonate radical on the degradation of oxytetracycline in UV-AOPs: Kinetics and mechanism

Carbonate radical (CO3•−), a selective oxidant, reacts readily with electron-rich compounds through electron transfer and/or hydrogen abstraction. In this study, the role of CO3•− in degrading oxytetracycline (OTC) by UV only, UV/H2O2 and UV/persulfate (UV/PS) advanced oxidation processes (AOPs) in the presence of HCO3− or CO32− was investigated. For UV only process, the presence of photosensitizers, i.e., nitrate (NO3−) and natural organic matter (NOM), had different impacts on OTC degradation, i.e., an enhancing effect by NO3− due to the generation of HO• and a slight inhibiting effect by NOM possibly due to a light scattering effect. Differently for UV/H2O2 and UV/PS processes, the presence of NO3− hardly influenced the destruction of OTC. Generation of CO3•− presented a positive role on OTC degradation by UV/NO3−/HCO3−. Such influence was also observed in the two studied AOPs in the presence of both bicarbonate and other natural water constituents. When various natural water samples from different sources were used as reaction matrices, UV only and UV/H2O2 showed an inhibiting effect while UV/PS demonstrated a comparable or even promoting effect in OTC decomposition. After elucidating the potential contribution of UV direct photolysis via excited state OTC* at an elevated reaction pH condition, putative OTC transformation byproducts via CO3•− reaction were identified by ultra-high definition accurate-mass quadrupole time-of-flight tandem mass spectrometry (QTOF/MS). Five different reaction pathways were subsequently proposed, including hydroxylation (+16 Da), quinonization (+14 Da), demethylation (−14 Da), decarbonylation (−28 Da) and dehydration (−18 Da). The significant role of UV at high pH and CO3•− on OTC removal from contaminated water was therefore demonstrated both kinetically and mechanistically.

Ozonation, photocatalysis and photocatalytic ozonation of diuron. Intermediates identification

Aqueous 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) has been oxidized by ozonation, photocatalysis and photocatalytic ozonation. Diuron degradation takes place via radical pathway through hydroxyl radicals in those systems involving ozone. Diuron elimination in photocatalytic ozonation is not enhanced if compared to single ozonation; however, TOC removal was significantly improved. Specifically, 80% TOC removal in 2h was reached in photocatalytic ozonation while single ozonation just led to 25% TOC reduction. Photocatalysis required 9h to reach 25% TOC reduction. Ten transformation by-products generated during the application of the three technologies were tentatively identified by liquid chromatography–quadrupole time-of-flight mass spectrometry (LC–QTOF–MS/MS). Single ozonation and photocatalytic ozonation led to the formation and complete elimination of all by-products. Low weight carboxylic acids evolution suggests that high TOC removal in photocatalytic ozonation is linked to its capacity to oxidize small oxygenated compounds and release of inorganic chloride and nitrate. Toxicity evolution to Vibrio fischeri in photocatalytic ozonation displayed an increase in inhibition at the initial stages (>90% of inhibition), followed by a decrease of this parameter as the reaction progressed. The final treated sample shows a lower toxicity than the initial one (55% vs 20%).

Correlating the properties of hydrogenated titania to reaction kinetics and mechanism for the photocatalytic degradation of bisphenol A under solar irradiation

Hydrogenation of a commercially available TiO2 anatase catalyst was carried out at several annealing temperatures in the range 400–800°C to improve its photocatalytic activity for the degradation of endocrine disruptor bisphenol A (BPA) under simulated solar irradiation. The prepared hydrogenated catalysts, as well as their counterparts calcined in air were characterized with respect to their morphological, optical and electronic properties by means of BET, XRD, XPS, DRS and UPS analyses. Thermal treatment under flowing hydrogen resulted in increased absorption at wavelengths below 400nm, as well as in the appearance of a broad and almost uniform absorption band in the visible region, the intensity of which increased with increase of annealing temperature. The latter was attributed to the creation of gap states in the hydrogenated samples, which was not observed for the samples calcined in air. Interestingly, sodium inherently present in the bulk of the pristine catalyst was found to diffuse at the surface and this was more pronounced for the hydrogenated samples prepared at temperatures above 700°C.The relative catalytic activity was tested to degrade 240μg/L BPA in pure water and it was found that the hydrogenated catalysts were more active than those calcined in air at the same temperatures. The maximum rate (0.0647min−1) was observed for the catalyst hydrogenated at 600°C, i.e. three times greater than the respective calcined catalyst. Higher annealing temperatures had a detrimental effect on photocatalytic activity and this may be associated with a collapse of the specific surface area. Other than the annealing temperature, the rate was also strongly dependent on the water matrix (slower for more complex matrices), BPA and catalyst concentration and the presence of electron acceptors.LC–MS/TOF analysis was employed to identify transformation by-products (TBPs) and elucidate reaction pathways. BPA degradation by hydrogenated catalysts seems to occur mainly through consecutive hydroxylation/oxidation reactions, as evidenced by the various oxygenated TBPs formed; conversely, scission of BPA through the isopropylidene group and further oxidation, yielding different para-substituted phenolic intermediates seems to be the main degradation route in the presence of calcined catalysts.

Aqueous chlorination of mefenamic acid: kinetics, transformation by-products and ecotoxicity assessment.

Mefenamic acid (Mfe) is one of the most frequently detected nonsteroidal anti-inflammatory drugs in the environment. This study investigated the kinetics and the transformation by-products of Mfe during aqueous chlorination. The potential ecotoxicity of the transformation by-products was also evaluated. In the kinetic study, the second-order rate constant (kapp) for the reaction between Mfe and free available chlorine (FAC) was determined at 25 ± 0.1 °C. The result indicated that the degradation of Mfe by FAC is highly pH-dependent. When the pH was increased from 6 to 8, it was found that the kapp for the reaction between Mfe and FAC was decreased from 16.44 to 4.4 M(-1) s(-1). Characterization of the transformation by-products formed during the chlorination of Mfe was carried out using liquid chromatography-quadrupole time-of-flight accurate mass spectrometry. Four major transformation by-products were identified. These transformation by-products were mainly formed through hydroxylation, chlorination and oxidation reactions. Ecotoxicity assessment revealed that transformation by-products, particularly monohydroxylated Mfe which is more toxic than Mfe, can be formed during aqueous chlorination.

Revealing the mechanism, pathways and kinetics of UV254nm/H2O2-based degradation of model active sunscreen ingredient PBSA

Transformation byproducts and pathways for the degradation of 2-phenylbenzimidazole-5-sulfonic acid (PBSA), a widely used organic active sunscreen agent, by UV254nm/H2O2 advanced oxidation process (AOP) were elucidated by mass spectrometry. Fourteen byproducts were identified, including environmentally hazardous benzamide (BD) and benzamidine (BZD). Beside of aromatic ring opening, desulfonation (−80Da) and hydroxylation (+16Da) were also two main reaction pathways. Degradation kinetics were compared with two PBSA structurally related compounds 2-phenylimidazole (2-PIZ) and benzimidazole (BZ) to estimate the application feasibility of the studied AOP. No apparent photolysis was noticed while the degradation of 1μM pollutants in the presence of 1mM H2O2 followed pseudo-first-order kinetics, with their observed rate constant (kobs) in the order of 2-PIZ>PBSA>BZ>BD>BZD, which is consistent with their respective second-order rate constant with hydroxyl radical. However, at high pollutant and oxidant concentrations, i.e., 50μM and 5mM, respectively, light attenuation contributed significantly to the change in kobs in the following manner, 2-PIZ∼BZ>PBSA∼BD>BZD. SO42− and NH4+ were the major inorganic mineral ions monitored in this study. Release of SO42− from PBSA degradation system reached 70% at 190min. At the same time interval, NH4+ were ⩽50% for all pollutants studied. Ultimate mineralization of PBSA, 2-PIZ, BZ, BD and BZD in terms of %TOC at 190min was found to be 23%, 38%, 45%, 57% and 62%, respectively. UV/H2O2 was shown to be efficient for the removal of organic sunscreen agents from water, however, special care toward the formation of environmentally hazardous byproducts should be considered.

Kinetics and mechanism investigation on the destruction of oxytetracycline by UV-254 nm activation of persulfate

Oxytetracycline (OTC), an important broad-spectrum antibiotic, has been detected extensively in various environmental systems, which may have a detrimental impact on ecosystem and human health through the development of drug resistant bacteria and pathogens. In this study, the degradation of OTC was evaluated by UV-254nm activated persulfate (PS). The observed UV fluence based pseudo first-order rate constant (kobs) was found to be the highest at near neutral pH conditions (pH 5.5–8.5). Presence of various natural water constituents had different effects on OTC degradation, with a significant enhancement in the presence of bicarbonate or Cu2+. Limited elimination of total organic carbon (TOC) and PS was observed during the mineralization of OTC. Transformation byproducts in the presence and absence of hydroxyl radical scavenging agent tert-butanol (t-BuOH) were identified using ultra-high definition accurate-mass quadrupole time-of-flight liquid chromatography/mass spectrometer (LC-QTOF/MS). Potential OTC degradation mechanism was subsequently proposed revealing four different reaction pathways by SO4− reaction including hydroxylation (+16Da), demethylation (−14Da), decarbonylation (−28Da) and dehydration (−18Da). This study suggests that UV-254nm/PS is a promising treatment technology for the control of water pollution caused by emerging contaminants such as OTC.

Study on Pt-structured anodic alumina catalysts for catalytic combustion of toluene: Effects of competitive adsorbents and competitive impregnation methods

Novel competitive impregnation methods were used to prepare high dispersion Pt-structured anodic alumina catalysts. It is found that competitive adsorbents owning different acidity result in different Pt loading amount and also exert great effects on Pt distribution, particle size and redox ability. The suitable adsorption ability of lactic acid led to its best activity for catalytic combustion of toluene. Co-competitive and pre-competitive impregnation methods were also compared and the mechanisms of two competitive methods were proposed. Co-competitive impregnation made Pt distribute more uniformly through pore channels and resulted in better catalytic activity, because of the weaker spatial constraint effect of lactic acid. Furthermore, the optimized Pt-structured anodic alumina catalyst also showed a good chlorine-resistance under moisture atmosphere, because water could promote the reaction of dichloromethane (DCM) transformation and clean chloride by-products to release more active sites.

Aqueous chlorination of acebutolol: kinetics, transformation by-products, and mechanism.

This study investigated the reaction kinetics and the transformation by-products of acebutolol during aqueous chlorination. Acebutolol is one of the commonly used β-blockers for the treatment of cardiovascular diseases. It has been frequently detected in the aquatic environment. In the kinetics study, the second-order rate constant for the reaction between acebutolol and chlorine (k app) was determined at 25 ± 0.1 °C. The degradation of acebutolol by free available chlorine was highly pH dependence. When the pH increased from 6 to 8, it was found that the k app for the reaction between acebutolol and free available chlorine was increased from 1.68 to 11.2 M(-1) min(-1). By comparing with the reported k app values, the reactivity of acebutolol toward free available chlorine was found to be higher than atenolol and metoprolol but lower than nadolol and propranolol. Characterization of the transformation by-products formed during the chlorination of acebutolol was carried out using liquid chromatography-quadrupole time-of-flight high-resolution mass spectrometry. Seven major transformation by-products were identified. These transformation by-products were mainly formed through dealkylation, hydroxylation, chlorination, and oxidation reactions.

Sono-activated persulfate oxidation of bisphenol A: Kinetics, pathways and the controversial role of temperature

The sonochemical degradation of bisphenol A (BPA) in the presence of sodium persulfate (SPS) was investigated at 20kHz. Experiments were performed at 110–450μg/L BPA and 1–100mg/L SPS concentration and an ultrasound power density between 4 and 60W/L. The liquid bulk temperature was either kept constant at 30°C or left uncontrolled and gradually increased up to 80°C. BPA degradation occurs due to the combined action of hydroxyl radicals generated by the ultrasound and sulfate radicals generated by SPS sonolysis and this was confirmed with experiments with methanol and t-butanol as radical scavengers. Considerable thermal SPS activation can also occur at increased temperatures (60–80°C) although the enhanced formation of sulfate radicals is compensated by a decrease in sonochemical activity. Kinetics can be approached by a pseudo-first order expression with the apparent rate constant decreasing with increasing BPA concentration; this implies that the actual order is below first. The rate increases with increasing power density and SPS concentration and decreases at alkaline conditions (i.e. pH=9) and in the presence of inorganic and organic constituents (e.g. bicarbonate, humic acid etc) typically found in environmental matrices.Liquid chromatography time of flight mass spectrometry (LC–TOF–MS) analysis revealed the formation of twelve transformation by-products that accompany BPA sonodegradation in the presence of SPS. Based on their evolution profiles, a reaction mechanism is proposed consisting of two major pathways: (i) hydroxylation that can occur mainly in the aromatic ring through HO, SO4− radical attack and to a lesser extent in methyl groups, through hydrogen abstraction by HO radicals, with subsequent O2 addition, and (ii) scission of the bond between the isopropylidene carbon and the phenyl group.

Kinetics of ethyl paraben degradation by simulated solar radiation in the presence of N-doped TiO2 catalysts

Ethyl paraben (EP), an emerging micro-pollutant representative of the parabens family, has been subject to photocatalytic degradation under simulated solar radiation at a photon flux of 1.3·10−4 E/(m2 s). Six nitrogen-doped titania catalysts synthesized by annealing a sol–gel derived TiO2 powder under ammonia flow and their un-doped counterparts, calcined in air at different temperatures in the range 450–800 °C, were compared under solar and visible light and the most active one (N-doped TiO2 calcined at 600 °C) was used for further tests.Experiments were performed at EP concentrations between 150 and 900 μg/L, catalyst loadings between 100 and 1000 mg/L, pH between 3 and 9, different matrices (ultrapure water, water spiked with humic acids or bicarbonates, drinking water and secondary treated wastewater) and hydrogen peroxide between 10 and 100 mg/L. For EP concentrations up to 300 μg/L, the degradation rate can be approached by first order kinetics but then shifts to lower order as the concentration increases. The rate increases linearly with catalyst loading up to 750 mg/L and hydrogen peroxide up to 100 mg/L. Near-neutral (pH = 6.5–7.5) and alkaline conditions (pH = 9) do not affect degradation, which is reduced at acidic pH. The presence of humic acids at 10–20 mg/L impedes degradation due to the competition with EP for the oxidizing species and this is more pronounced in actual wastewater matrices.UPLC-ESI-HRMS and HPLC-DAD were employed to follow EP concentration changes, as well as identify and quantify transformation by-products during the early stages of the reaction. Five such products were successfully detected and, based on their concentration–time profiles, a reaction network for the degradation of EP is proposed. Hydroxyl radical reactions appear to prevail during the initial steps as evidenced by the rapid formation of hydroxylated and dealkylated intermediates.

Degradation kinetics and pathways of three calcium channel blockers under UV irradiation

Calcium channel blockers (CCBs) are a group of pharmaceuticals widely prescribed to lower blood pressure and treat heart diseases. They have been frequently detected in wastewater treatment plant (WWTP) effluents and downstream river waters, thus inducing a potential risk to aquatic ecosystems. However, little is known about the behavior and fate of CCBs under UV irradiation, which has been adopted as a primary disinfection method for WWTP effluents. This study investigated the degradation kinetics and pathways of three commonly-used CCBs, including amlodipine (AML), diltiazem (DIL), and verapamil (VER), under UV (254 nm) irradiation. The chemical structures of transformation byproducts (TBPs) were first identified to assess the potential ecological hazards. On that basis, a generic solid-phase extraction method, which simultaneously used four different cartridges, was adopted to extract and enrich the TBPs. Thereafter, the photo-degradation of target CCBs was performed under UV fluences typical for WWTP effluent disinfection. The degradation of all three CCBs conformed to the pseudo-first-order kinetics, with rate constants of 0.031, 0.044 and 0.011min−1 for AML, DIL and VER, respectively. By comparing the MS2 fragments and the evolution (i.e., formation or decay) trends of identified TBPs, the degradation pathways were proposed. In the WWTP effluent, although the target CCBs could be degraded, several TBPs still contained the functional pharmacophores and reached peak concentrations under UV fluences of 40–100 mJ cm−2.

Identification of unwanted photoproducts of cosmetic preservatives in personal care products under ultraviolet-light using solid-phase microextraction and micro-matrix solid-phase dispersion

The photochemical transformation of widely used cosmetic preservatives including benzoates, parabens, BHA, BHT and triclosan has been investigated in this work applying an innovative double-approach strategy: identification of transformation products in aqueous photodegradation experiments (UV-light, 254nm), followed by targeted screening analysis of such photoproducts in UV-irradiated cosmetic samples. Solid-phase microextraction (SPME) was applied, using different fiber coatings, in order to widen the range of detectable photoproducts in water, whereas UV-irradiated personal care products (PCPs) containing the target preservatives were extracted by micro-matrix solid-phase dispersion (micro-MSPD). Both SPME and micro-MSPD-based methodologies were successfully optimized and validated. Degradation kinetics of parent species, and photoformation of their transformation by-products were monitored by gas chromatography coupled to mass spectrometry (GC–MS). Thirty nine photoproducts were detected in aqueous photodegradation experiments, being tentatively identified based on their mass spectra. Transformation pathways between structurally related by-products, consistent with their kinetic behavior were postulated. The photoformation of unexpected photoproducts such as 2- and 4-hydroxybenzophenones, and 2,8-dichlorodibenzo-p-dioxin in PCPs are reported in this work for the first time.

Monte Carlo simulations of the transformation and removal of Ag, TiO2, and ZnO nanoparticles in wastewater treatment and land application of biosolids

The use of nano-enabled materials in industry and consumer products is increasing rapidly and with it, the more imperative it becomes to understand the consequences of such materials entering the environment during production, use or disposal. The novel properties of engineered nanomaterials (ENMs) that make them desirable for commercial applications also present the possibility of impacting aquatic and terrestrial environments in ways that may differ from materials in bulk format. Modeling techniques are needed to proactively predict the environmental fate and transport of nanomaterials.A model for nanoparticle (NP) separation and transformation in water treatment was parameterized for three metal and metal-oxide NPs. Functional assays to determine NP specific distribution and transformation were used to parameterize the model and obtain environmentally relevant concentrations of NPs and transformation byproducts leaving WWTPs in effluent and biosolids. All three NPs were predicted to associate >90% with the solid phase indicating significant accumulation in the biosolids. High rates of transformation for ZnO and Ag NPs resulted in ~97% transformation of the NPs that enter the plant despite differences in transformation rate in aerobic versus anaerobic environments. Due to high insolubility and negligible redox transformation, the only process predicted to impact TiO2 NP fate and transport in WWTPs was distribution between the solid and liquid phases. Subsequent investigation of ZnO NP species fate and transport when land applied in biosolids indicated that steady state concentrations of ZnO phases would likely be achieved after approximately 150days under loading conditions of biosolids typical in current practice.