Effect Of Water Matrix Research Articles

Effect of ozonation on minocycline degradation and N-Nitrosodimethylamine formation

ABSTRACTThe objective of this study was to assess reactivity of Minocycline (MNC) towards ozone and determine the effects of ozone dose, pH value, and water matrix on MNC degradation as well as to characterize N-Nitrosodimethylamine (NDMA) formation from MNC ozonation. The MNC initial concentration of the solution was set in the range of 2–20 mg/L to investigate NDMA formation during MNC ozonation. Four ozone doses (22.5, 37.2, 58.0, and 74.4 mg/min) were tested to study the effect of ozone dose. For the evaluation of effects of pH value, pH was adjusted from 5 to 9 in the presence of phosphate buffer. MNC ozonation experiments were also conducted in natural water to assess the influence of water matirx. The influence of the typical component of natural water was also investigated with the addition of HA and NaHCO3 solution. Results indicated that ozone was effective in MNC removal. Consequently, NDMA and dimethylamine (DMA) were generated from MNC oxidation. Increasing pH value enhanced MNC removal but led to greater NDMA generation. Water matrices, such as HCO3− and humic acid, affected MNC degradation. Conversely, more NDMA accumulated due to the inhibition of NDMA oxidation by oxidant consumption. Though ⋅OH can enhance MNC degradation, ozone molecules were heavily involved in NDMA production. Seven transformation products were identified. However, only DMA and the unidentified tertiary amine containing DMA group contributed to NDMA formation.

Application of calcium peroxide for efficient removal of triamcinolone acetonide from aqueous solutions: Mechanisms and products

There are numerous studies identifying the presence and toxicity of glucocorticoids (GCs) in water; however, limited studies reported effective GC removal technologies. This study researched the efficiency of calcium peroxide (CaO2) in removing GC in wastewater treatment plants (WWTPs) with triamcinolone acetonide (TA) as the representative. Effects of CaO2 dosage, initial pH, and water matrix were investigated. The functional reactive oxygen species (ROS) during TA removal was tested. Specifically, TA degradation intermediates by CaO2 oxidation were identified for the first time. GC toxicity change during TA removal was deduced. The results indicated that CaO2 treatment can be an effective method for TA removal and toxicity decrease. At the reaction time of 60 min, more than 78% of TA can be degraded with CaO2 at 0.05–4 g L−1. The TA removal efficiency increased with the increase of CaO2 dosage. The optimal initial pH value is 6.8. HCO3−, Cl−, and NO3− had inhibitive effects on TA removal while SO42− had no effect and PO43− had positive effect. Humic acid (HA) had positive effects on TA removal because of its obvious adsorption effects. The HO and O2− released by CaO2 are the functional ROS for TA removal, among which HO is the most important one. Besides the oxidation of HO and O2−, the adsorption effects of CaO2 and Ca(OH)2 and the hydrolysis at alkaline conditions may also contribute to TA removal. Six intermediates were revealed during TA degradation, indicating the decrease in GC activity.

Enhanced degradation of Bisphenol A (BPA) by peroxymonosulfate with Co3O4-Bi2O3 catalyst activation: Effects of pH, inorganic anions, and water matrix

In this study, a novel Co3O4-Bi2O3 catalyst was synthesized using a microwave-assistant method, and the corresponding characteristics were studied through XRD, SEM, and N2 adsorption. As a peroxymonosulfate (PMS) activator, the catalytic activity of the synthesized catalyst was evaluated on Bisphenol A (BPA) removal, and the result showed that Co3O4-Bi2O3 catalyst promoted BPA degradation, where 100% BPA was degraded within 15 min under the condition of [catalyst] = 0.1 g·L−1 and [PMS]/[BPA]molar = 5. The Co3O4-Bi2O3/PMS system presented a good catalytic activity when the solution pH varied from 3.0 to 11.0. Under the different concentrations of various inorganic anions in the Co3O4-Bi2O3/PMS system, Cl− showed an inhibited effect at low concentration and a promoted effect at high concentration. CO32− showed a slight inhibited effect, while H2PO4− showed a considerable inhibited effect. Additionally, both NO3− and SO42− showed a negligible effect on BPA removal. For the real water bodies, both the drinking water and tap water showed a slight decrease in degradation efficiency of BPA but a distinctly negative effect on BPA mineralization, which might be contributed to the competition between BPA and indigenous organic matters in the two water matrices for their oxidation by radical species. The quenching experiment was enforced and it was found that both SO4− and OH on the surface-bound of catalyst were the main active radicals in this system. Overall, the Co3O4-Bi2O3 catalyst as a PMS activator is a promising catalyst in PMS activation for sulfate radical-based wastewater treatment.

Low levels of iron enhance UV/H2O2 efficiency at neutral pH

While the presence of iron is generally not seen as favorable for UV-based treatment systems due to lamp fouling and decreased UV transmittance, we show that low levels of iron can lead to improvements in the abatement of chemicals in the UV-hydrogen peroxide advanced oxidation process. The oxidation potential of an iron-assisted UV/H2O2 (UV254 + H2O2 + iron) process was evaluated at neutral pH using iron levels below USEPA secondary drinking water standards (<0.3 mg/L). Para-chlorobenzoic acid (pCBA) was used as a hydroxyl radical (HO) probe to quantify HO steady state concentrations. Compounds degraded by different mechanisms including, carbamazepine (CBZ, HO oxidation) and N-nitrosodimethylamine (NDMA, direct photolysis), were used to investigate the effect of iron on compound degradation for UV/H2O2 systems. The effects of iron species (Fe2+ and Fe3+), iron concentration (0–0.3 mg/L), H2O2 concentration (0–10 mg/L) and background water matrix (low-carbon tap (LCT) and well water) on HO production and compound removal were examined. Iron-assisted UV/H2O2 efficiency was most influenced by the target chemical and the water matrix. Added iron to UV/H2O2 was shown to increase the steady-state HO concentration by approximately 25% in all well water scenarios. While CBZ removal was unchanged by iron addition, 0.3 mg/L iron improved NDMA removal rates in both LCT and well water matrices by 15.1% and 4.6% respectively. Furthermore, the combination of UV/Fe without H2O2 was also shown to enhance NDMA removal when compared to UV photolysis alone indicating the presence of degradation pathways other than HO oxidation.

Photochemical degradation of the carbapenem antibiotics imipenem and meropenem in aqueous solutions under solar radiation

This paper deals with the photochemical fate of two representative carbapenem antibiotics, namely imipenem and meropenem, in aqueous solutions under solar radiation. The analytical method employed for the determination of the target compounds in various aqueous matrices, such as ultrapure water, municipal wastewater treatment plant effluents, and river water, at environmentally relevant concentrations, was liquid chromatography coupled with hybrid triple quadrupole-linear ion trap-mass spectrometry. The absorption spectra of both compounds were measured in aqueous solutions at pH values from 6 to 8, and both compounds showed a rather strong absorption band centered at about 300 nm, while their molar absorption coefficient was in the order from 9 × 103–104 L mol−1 cm−1. The kinetics of the photochemical degradation of the target compounds was studied in aqueous solutions under natural solar radiation in a solar reactor with compound parabolic collectors. It was found that the photochemical degradation of both compounds at environmentally relevant concentrations follows first order kinetics and the quantum yield was in the order of 10−3 mol einsten−1. Several parameters were studied, such as solution pH, the presence of nitrate ions and humic acids, and the effect of water matrix. In all cases, it was found that the presence of various organic and inorganic constituents in the aqueous matrices do not contribute significantly, either positively or negatively, to the photochemical degradation of both compounds under natural solar radiation. In a final set of photolysis experiments, the effect of the level of irradiance was studied under simulated solar radiation and it was found that the quantum yield for the direct photodegradation of both compounds remained practically constant by changing the incident solar irradiance from 28 to 50 W m−2.

Degradation of propyl paraben by activated persulfate using iron-containing magnetic carbon xerogels: investigation of water matrix and process synergy effects.

An advanced oxidation process comprising an iron-containing magnetic carbon xerogel (CX/Fe) and persulfate was tested for the degradation of propyl paraben (PP), a contaminant of emerging concern, in various water matrices. Moreover, the effect of 20kHz ultrasound or light irradiation on process performance was evaluated. The pseudo-first order degradation rate of PP was found to increase with increasing SPS concentration (25-500mg/L) and decreasing PP concentration (1690-420μg/L) and solution pH (9-3). Furthermore, the effect of water matrix on kinetics was detrimental depending on the complexity (i.e., wastewater, river water, bottled water) and the concentration of matrix constituents (i.e., humic acid, chloride, bicarbonate). The simultaneous use of CX/Fe and ultrasound as persulfate activators resulted in a synergistic effect, with the level of synergy (between 35 and 50%) depending on the water matrix. Conversely, coupling CX/Fe with simulated solar or UVA irradiation resulted in a cumulative effect in experiments performed in ultrapure water.

Oxidation of Tris (2-chloroethyl) phosphate in aqueous solution by UV-activated peroxymonosulfate: Kinetics, water matrix effects, degradation products and reaction pathways

The feasibility of UV-activated peroxymonosulfate (PMS) technology for the degradation of Tris (2-chloroethyl) phosphate (TCEP) in an aqueous solution was investigated in this study. The conditions of [PMS]0: [TCEP]0 = 20:1, T = 25 ± 2 °C and pH = 5.5 ± 0.5 cause a 94.6% removal of TCEP (1 mg L−1) after 30 min of Hg lamp irradiation. The effects of operating parameters (the oxidant doses, pH and presence of typical cations (Fe3+, Cu2+, Ni2+, NH4+), anions (Cl−, HCO3−, NO3−, HPO42−) and humic acid (HA)) were evaluated. It was found that an increase of the PMS dose and the presence of Fe3+ could accelerate the reaction, while the anions and HA inhibited the reaction. Meanwhile, TCEP removal in various water matrices was compared, and the order for TCEP removal was as follows: ultrapure water > tap water > synthetic water > secondary clarifier effluent > Jiuxiang river water. Twenty-two oxidation products were identified using an electrospray time-of-flight mass spectrometer, and the degradation pathways mainly involved radicals' addition and CO bond cleavage. Furthermore, ECOSAR analysis revealed that the intermediate products during the TCEP oxidation process were generally not harmful to three typical aquatic species. Hence, UV/PMS can be used as an efficient technology to treat TCEP-containing water and wastewaters.

Degradation kinetics of tetracycline in aqueous solutions using peroxydisulfate activated by ultrasound irradiation: Effect of radical scavenger and water matrix

Degradation kinetics of the tetracycline antibiotic in aqueous solution was investigated using sulfate radicals under ultrasound irradiation. The effect of various operational parameters including initial tetracycline concentration, initial peroxydisulfate concentration, solution pH, reaction time, temperature, ultrasound power, the presence of natural organic matter, radical scavenger (tert-butyl alcohol and methanol), as well as the chemical composition of water using ultrapure water, drinking water, and secondary effluent on the degradation efficiency of tetracycline were studied. The preliminary studies were performed using only peroxydisulfate, ultrasound and ultrasound activated peroxydisulfate. The results indicated that tetracycline degradation rate increased with the increase of initial peroxydisulfate concentration, temperature and ultrasonic power, but decreased with the increase of initial tetracycline concentration. The tetracycline degradation rate was highly dependent of initial pH of the solution. The degradation of tetracycline followed the first-order kinetics. The addition of humic acid in concentrations above 10mg·L−1 decreased the degradation rate of tetracycline, although the effect could be compensated using higher concentrations of peroxydisulfate. The role of active radicals (sulfate and hydroxyl radicals) was investigated using radical scavengers of methanol and tert-butyl alcohol. Under optimum operational conditions, 96.5% of tetracycline removal was achieved with chemical oxygen demand and total organic carbon removal of about 74% and 61.2%, respectively. The degradation rate of tetracycline was higher in drinking water compared to ultrapure water. Finally, the intermediates were identified and the possible degradation pathway of tetracycline was investigated. Overall, ultrasound activated peroxydisulfate was found to be a promising process for tetracycline degradation in aqueous solutions.

Comparative Evaluation of Photo-Chemical AOPs for Ciprofoxacin Degradation: Elimination in Natural Waters and Analysis of pH Effect, Primary Degradation By-Products, and the Relationship with the Antibiotic Activity

In this work, ciprofloxacin (CIP) degradation is investigated using different photo-chemical advanced oxidation processes (AOPs): Fe2+/H2O2/UV, TiO2/UV, and H2O2/UV. At natural pH, direct oxidation at the photo-generated holes showed to be the main pathway during TiO2/UV process, while H2O2/UV and Fe2+/H2O2/UV degradation mainly occurred by hydroxyl radical attack. The identification of degradation by-products confirmed the differences in the degradation pathways. Water matrix effects were also investigated by evaluating the influence of the initial pH and testing CIP degradation in mineral natural water and distilled water. Significant differences were observed associated to the pH, the H2O2/UV system being the less affected process. Natural water showed to be an inhibitor medium for the tested photo-chemical processes. Interestingly, H2O2/UV system showed again to be not considerably affected by the natural water matrix. Additionally, degradation extent of treated solutions was determined by the mineralization level (TOC removal) and the antimicrobial activity (AA) elimination using Staphylococcus aureus and Escherichia coli as probe microorganisms. Despite mineralization was no reached in any case, AA elimination was promoted by all processes suggesting the formation of by-products with non-antibiotic character. However, due to the particular degradation pathway, interesting differences were observed according to the type of bacteria when TiO2 photo-catalysis was used.

Removal of antibiotics in a parallel-plate thin-film-photocatalytic reactor: Process modeling and evolution of transformation by-products and toxicity

Photocatalytic degradation of sulfamethoxazole (SMX) antibiotic has been studied under recycling batch and homogeneous flow conditions in a thin-film coated immobilized system namely parallel-plate (PPL) reactor. Experimentally designed, statistically evaluated with a factorial design (FD) approach with intent to provide a mathematical model takes into account the parameters influencing process performance. Initial antibiotic concentration, UV energy level, irradiated surface area, water matrix (ultrapure and secondary treated wastewater) and time, were defined as model parameters. A full of 25 experimental design was consisted of 32 random experiments. PPL reactor test experiments were carried out in order to set boundary levels for hydraulic, volumetric and defined defined process parameters. TTIP based thin-film with polyethylene glycol+TiO2 additives were fabricated according to pre-described methodology. Antibiotic degradation was monitored by High Performance Liquid Chromatography analysis while the degradation products were specified by LC–TOF-MS analysis. Acute toxicity of untreated and treated SMX solutions was tested by standard Daphnia magna method. Based on the obtained mathematical model, the response of the immobilized PC system is described with a polynomial equation. The statistically significant positive effects are initial SMX concentration, process time and the combined effect of both, while combined effect of water matrix and irradiated surface area displays an adverse effect on the rate of antibiotic degradation by photocatalytic oxidation. Process efficiency and the validity of the acquired mathematical model was also verified for levofloxacin and cefaclor antibiotics. Immobilized PC degradation in PPL reactor configuration was found capable of providing reduced effluent toxicity by simultaneous degradation of SMX parent compound and TBPs.

Selecting the best AOP for isoxazolyl penicillins degradation as a function of water characteristics: Effects of pH, chemical nature of additives and pollutant concentration

To provide new insights toward the selection of the most suitable AOP for isoxazolyl penicillins elimination, the degradation of dicloxacillin, a isoxazolyl penicillin model, was studied using different advanced oxidation processes (AOPs): ultrasound (US), photo-Fenton (UV/H2O2/Fe2+) and TiO2 photocatalysis (UV/TiO2). Although all processes achieved total removal of the antibiotic and antimicrobial activity, and increased the biodegradability level of the solutions, significant differences concerning the mineralization extend, the pH of the solution, the pollutant concentration and the chemical nature of additives were found. UV/TiO2 reached almost complete mineralization; while ∼10% mineralization was obtained for UV/H2O2/Fe2+ and practically zero for US. Effect of initial pH, mineral natural water and the presence of organic (glucose, 2-propanol and oxalic acid) were then investigated. UV/H2O2/Fe2+ and US processes were improved in acidic media, while natural pH favored UV/TiO2 system. According to both the nature of the added organic compound and the process, inhibition, no effect or enhancement of the degradation rate was observed. The degradation in natural mineral water showed contrasting results according to the antibiotic concentration: US process was enhanced at low concentration of dicloxacillin followed by detrimental effects at high substrate concentrations. A contrary effect was observed during photo-Fenton, while UV/TiO2 was inhibited in all of cases. Finally, a schema illustrating the enhancement or inhibiting effects of water matrix is proposed as a tool for selecting the best process for isoxazolyl penicillins degradation.

Identification of transformation products during advanced oxidation of diatrizoate: Effect of water matrix and oxidation process

Removal of micropollutants from reverse osmosis (RO) brines of wastewater desalination by oxidation processes is influenced by the scavenging capacity of brines components, resulting in the accumulation of transformation products (TPs) rather than complete mineralization. In this work the iodinated contrast media diatrizoate (DTZ) was used as model compound due to its relative resistance to oxidation. Identification of TPs was performed in ultrapure water (UPW) and RO brines applying nonthermal plasma (NTP) and UVA-TiO2 as oxidation techniques. The influence of main RO brines components in the formation and accumulation of TPs, such as chloride, bicarbonate alkalinity and humic acid, was also studied during UVA-TiO2. DTZ oxidation pattern in UPW resulted similar in both UVA-TiO2 and NTP achieving 66 and 61% transformation, respectively. However, DTZ transformation in RO brines was markedly lower in UVA-TiO2 (9%) than in NTP (27%). These differences can be attributed to the synergic effect of RO brines components during NTP. Moreover, reactive species other than hydroxyl radical contributed to DTZ transformation, i.e., direct photolysis in UVA-TiO2 and direct photolysis + O3 in NTP accounted for 16 and 23%, respectively. DTZ transformation led to iodide formation in both oxidation techniques but it further oxidized to iodate by ozone in NTP. In total 14 transformation products were identified in UPW of which 3 were present only in UVA-TiO2 and 2 were present exclusively in NTP; 5 of the 14 TPs were absent in RO brines. Five of them were new and were denoted as TP-474A/B, TP-522, TP-586, TP-602, TP-628. TP-522 (mono-chlorinated) was elucidated only in presence of high chloride titer-synthetic water matrix in NTP, most probably formed by active chlorine species generated in situ. TPs accumulation in RO brines was markedly different in comparison to UPW. This denotes the influence of RO brines components in the formation of reactive species that could further attack DTZ/TPs and/or scavenging performed by these brine components that could limit further TPs degradation. Five plausible degradation pathways are proposed for DTZ transformation in UPW.

ZnO nanoflowers photocatalysis of norfloxacin: Effect of triangular silver nanoplates and water matrix on degradation rates

Abstract Norfloxacin (NF) is an effective antimicrobial drug that poses a threat to human health because of its environmental residues. In this research, ZnO nanoflowers and triangular silver nanoplates (T-Ag) were synthesized using a facile sol–gel method. The synergistic photocatalytic effects of the adding different triangular silver nanoplates concentration over ZnO nanoflowers on the NF removal under visible light was studied for the first time. Photodegradation results demonstrated that T-Ag could significantly enhance the activity of ZnO nanoflowers. The degradation efficiency of NF by T-Ag/ZnO nanoflowers was affected in the different water matrices, including ultra-pure, tap, and river water. The effects of the dosage of ZnO nanoflowers, initial NF concentration, and pH on the photocatalytic activity of ZnO nanoflowers were also explored. The results show that the highest rate constant for the degradation of NF is obtained with 1 mg L −1 of T-Ag, 0.1 g L −1 of ZnO, initial NF concentration of 10 mg L −1 , and pH of 11 in ultra-pure water. The possible mechanism of the photocatalytic degradation of NF using T-Ag/ZnO nanoflowers through the addition of scavenger agents (i.e., EDTA and methanol) was also studied.

Photocatalytic Degradation of Polycyclic Aromatic Hydrocarbons in Offshore Produced Water: Effects of Water Matrix

AbstractTo demonstrate the feasibility of photocatalysis for the removal of polycyclic aromatic hydrocarbons (PAHs) from offshore-produced water (OPW), the effects of water matrix were studied by comparing the performance of TiO2-induced photocatalysis in distilled water and OPW media. The effects of salinity, insoluble particulate matter, and organic composition were evaluated. The results showed the strong improvements with the addition of catalysts but the enhancement of photocatalysis was restricted by OPW media. The photocatalytic degradation of PAHs with high molecular weights was more sensitive to the variations of salinity and insoluble matter due to their lower solubility. The overall degradation of PAHs was strongly restricted by the organic composition in OPW particularly the aromatic compounds. The aromatic compounds played an important role as ultraviolet-photon absorbents and competed with the photodegradation of PAHs. Because of their abundance in OPW, these species had the most significant...

Degradation of 2,4-dichlorophenol by nanoscale calcium peroxide: Implication for groundwater remediation

Abstract In this study, a newly emerging oxidant nanoscale calcium peroxide (nCaO 2 ) was synthesized to degrade 2,4-dichlorophenol (2,4-DCP). nCaO 2 was prepared from nanoscale Ca(OH) 2 and H 2 O 2 and confirmed to be less than 150 nm in diameter and 62.23 m 2 · g −1 in specific surface area (SSA). For treating 2,4-DCP, the optimal ratio between Ca(OH) 2 and H 2 O 2 was 1:5. Compared with conventional CaO 2 , nCaO 2 was found to be more efficient for destructing 2,4-DCP. 2,4-DCP was completely degraded in 5 d by nCaO 2 while only 75.0% 2,4-DCP was destructed by conventional CaO 2 . The effects of solution pH and water matrix, including SO 4 2− , HCO 3 − and humic acid (HA) were examined. The reactive species in nCaO 2 system was investigated by photoluminescence (PL) technique and the quenching experiments. Results showed that hydroxyl radical (OH ) was the dominant reactive species for destructing 2,4-DCP. The major oxidation products identified in this study were 2-chlorophenol (2-CP), 4-chlorophenol (4-CP), phenol and benzoquinone (BQ). Our works gave an important insight into the use of nCaO 2 to degrade some organic contaminants which might provide some references for the application of nCaO 2 in chlorophenols contaminated groundwater remediation.

Enhanced formation of bromate and brominated disinfection byproducts during chlorination of bromide-containing waters under catalysis of copper corrosion products

Copper corrosion products (CCPs) in water distribution pipes may catalyze the reactions among disinfectant, natural organic matter (NOM), and bromide (Br−). This study investigated the simultaneous formation of bromate (BrO3−) and brominated disinfection byproducts (Br-DBPs) during chlorination of Br−-containing waters in the presence of three CCPs (i.e., CuO, Cu2O, and Cu2+). In a synthetic water, both oxidant decay and BrO3− formation were enhanced by CCPs, whereas the presence of humic acid (HA) significantly inhibited BrO3− formation due to its competition for HOBr to form Br-DBPs. In the HOClBr−CuO system, the BrO3− yield increased obviously with increasing CuO dose and initial Br− concentration, while the catalytic formation of Br-DBPs was rather limited. A molar conversion (Br− to BrO3−) of 22.1% was observed under CuO catalysis, compared with little conversion in the absence of CuO. In the HOClBr−Cu2O/Cu2+ systems, Cu2O or Cu2+ mainly enhanced the formation of Br-DBPs, with enhancement ratios of 69.9% and 50.1%, respectively. The degree of enhancement on Br-DBPs formation became more apparent with increasing pH, while that on BrO3− formation reached maximal at pH 7.6. The catalytic formation of Br-DBPs and BrO3− by CCPs was also verified in three filtered real waters, although to a lesser extent because of the water matrix effect. In mechanism, the CCPs promoted the formation of BrO3− and Br-DBPs through catalyzing the HOBr disproportionation pathway and the reaction of HOBr toward HA, respectively.

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.

Organic micropollutants (OMPs) in natural waters: Oxidation by UV/H2O2 treatment and toxicity assessment

Organic micropollutants (OMPs) are ubiquitous in natural waters even in places where the human activity is limited. The presence of OMPs in natural water sources for human consumption encourages the evaluation of different water purification technologies to ensure water quality. In this study, the Biobío river (Chile) was selected since the watershed includes urban settlements and economic activities (i.e. agriculture, forestry) that incorporate a variety of OMPs into the aquatic environment, such as pesticides, pharmaceuticals and personal care products. Atrazine (herbicide), caffeine (psychotropic), diclofenac (anti-inflammatory) and triclosan (antimicrobial) in Biobío river water and in different stages of a drinking and two wastewater treatment plants downstream Biobío river were determined using solid phase extraction (SPE) and liquid chromatography/tandem mass spectrometry (LC-MS/MS) and electrospray ionization (ESI). Quantification of these four compounds showed concentrations in the range of 8 ± 2 to 55 ± 10 ng L−1 in Biobío river water, 11 ± 2 to 74 ± 21 ng L−1 in the drinking water treatment plant, and 60 ± 10 to 15,000 ± 1300 ng L−1 in the wastewater treatment plants. Caffeine was used as an indicator of wastewater discharges.Because conventional water treatment technologies are not designed to eliminate some emerging organic pollutants, alternative treatment processes, UV and UV/H2O2, were employed. The transformation of atrazine, carbamazepine (antiepileptic), diclofenac and triclosan was investigated at laboratory scale. Both processes were tested at different UV doses and the Biobío river water matrix effects were evaluated. Initial H2O2 concentration used was 10 mg L−1. Results showed that, the transformation profile obtained using UV/H2O2 at UV doses up to 900 mJ cm−2, followed the trend of diclofenac > triclosan > atrazine > carbamazepine. Furthermore acute toxicity tests with Daphnia magna were carried out after UV/H2O2 treatments of the OMPs mixture studied. At the lower UV doses tested (300 mJ cm−2) a higher toxicity was observed, suggesting the formation of toxic intermediates in the course of the reaction. As expected, at higher UV doses the toxicity declined. Considering the treatment of the mixture of ATZ, CBZ, DCL and TCS with a UV dose of 1200 mJ cm−2 and 10 mg L−1 of H2O2 the acute toxicity results exhibits values for Daphnia magna immobilization equal to 20 and 42% evaluated after 24 and 48 h, respectively.

Oxidation of the odorous compound 2,4,6-trichloroanisole by UV activated persulfate: Kinetics, products, and pathways

The transformation efficiency and products of an odorous compound 2,4,6-trichloroanisole (TCA) at the wavelength of 254 nm in the presence of persulfate were investigated for the first time. The effects of water matrix (i.e., natural organic matter (NOM), pH, carbonate/bicarbonate (HCO3−/CO32−), and chloride ions (Cl−)) were evaluated. The second order rate constant of TCA reacting with sulfate radical (SO4−) was determined to be (3.72 ± 0.10) × 109 M−1 s−1. Increasing dosage of persulfate increased the observed pseudo-first-order rate constant for TCA degradation (kobs), and the contribution of SO4− to TCA degradation was much higher than that of HO at each experimental condition. Degradation rate of TCA decreased with pH increasing from 4.0 to 9.0, which could be explained by the lower radical scavenging effect of dihydrogen phosphate than hydrogen phosphate in acidic condition (pH < 6). NOM significantly decreased kobs due to the effects of radical scavenging and UV absorption with the former one being dominant. kobs decreased from 2.32 × 10−3 s−1 to 0.92 × 10−3 s−1 with the CO32−/HCO3− concentration increased from 0.5 mM to 10 mM in the UV/persulfate process, while kobs slightly decreased from 2.54 × 10−3 s−1 in the absence of Cl− to 2.10 × 10−3 s−1 in the presence of 10 mM Cl−. Most of these kinetic results could be described by a steady-state kinetic model. Furthermore, liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry at powerful precursor ion scan approach was used to selectively detect oxidation products of TCA. It was found that 2,4,6-trichorophenol (TCP) was the major oxidation product (i.e., the initial yield of TCP was above 90%). The second order rate constant between TCP and SO4− was estimated to be (4.16 ± 0.20) × 109 M−1 s−1. In addition, three products (i.e., 2,6-dichloro-1,4-benzoquinone and two aromatic ring-opening products) were detected in the reaction of TCP with SO4−, which also appeared in the oxidation of TCA in the UV/persulfate process. A tentative pathway was proposed, where the initial one-electron oxidation of TCA by SO4− and further reactions (e.g., ipso-hydroxylation and aromatic ring-cleavage) of the formed cation intermediate TCA were involved.

Kinetics and pathways of ibuprofen degradation by the UV/chlorine advanced oxidation process

The UV/chlorine advanced oxidation process (AOP), which forms reactive species such as hydroxyl radicals (HO) and reactive chlorine species (RCS) such as chlorine atoms (Cl) and Cl2−, is being considered as an alternative to the UV/H2O2 AOP for the degradation of emerging contaminants. This study investigated the kinetics and pathways of the degradation of a recalcitrant pharmaceutical and personal care product (PPCP)—ibuprofen (IBP)—by the UV/chlorine AOP. The degradation of IBP followed the pseudo first-order kinetics. The first-order rate constant was 3.3 times higher in the UV/chlorine AOP than in the UV/H2O2 AOP for a given chemical molar dosage at pH 6. The first-order rate constant decreased from 3.1 × 10−3 s−1 to 5.5 × 10−4 s−1 with increasing pH from 6 to 9. Both HO and RCS contributed to the degradation, and the contribution of RCS increased from 22% to 30% with increasing pH from 6 to 9. The degradation was initiated by HO-induced hydroxylation and Cl-induced chlorine substitution, and sustained through decarboxylation, demethylation, chlorination and ring cleavage to form more stable products. Significant amounts of chlorinated intermediates/byproducts were formed from the UV/chlorine AOP, and four chlorinated products were newly identified. The yield of total organic chlorine (TOCl) was 31.6 μM after 90% degradation of 50 μM IBP under the experimental conditions. The known disinfection by-products (DBPs) comprised 17.4% of the TOCl. The effects of water matrix in filtered drinking water on the degradation were not significant, demonstrating the practicality of the UV/chlorine AOP for the control of some refractory PPCPs. However, the toxicity of the chlorinated products should be further assessed.