Elena Rodriguez

Photolysis of model emerging contaminants in ultra-pure water: kinetics, by-products formation and degradation pathways.

The photolysis of five frequent emerging contaminants (Benzotriazole, Chlorophene, N,N-diethyl-m-toluamide or DEET, Methylindole, and Nortriptyline HCl) was investigated in ultrapure water under monochromatic ultraviolet radiation at 254 nm and by a combination of UV and hydrogen peroxide. The results revealed that the photolysis rates followed first-order kinetics, with rate constant values depending on the nature of the specific compound, the pH, and the presence or absence of the scavenger tert-butanol. Quantum yields were also determined and values in the range of 53.8 × 10⁻³ - 9.4 × 10⁻³ mol E⁻¹ for Benzotriazole, 525 × 10⁻³ - 469 × 10⁻³ mol E⁻¹ for Chlorophene, 2.8 × 10⁻³ - 0.9 × 10⁻³ mol E⁻¹ for DEET, 108 × 10⁻³ - 165 × 10⁻³ mol E⁻¹ for Methylindole, and 13.8 × 10⁻³ - 15.0 × 10⁻³ mol E⁻¹ for Nortriptyline were obtained. The study also found that the UV/H₂O₂ process enhanced the oxidation rate in comparison to direct photolysis. High-performance liquid chromatography coupled to electrospray ionization quadrupole time-of-flight mass spectrometry (HPLC-ESI-QTOF-MS) technique was applied to the concentrations evaluation and further identification of the parent compounds and their by-products, which allowed the proposal of the degradation pathways for each compound. Finally, in order to assess the aquatic toxicity in the photodegradation of these compounds, the Vibrio fischeri acute toxicity test was used, and the results indicated an initial increase of this parameter in all cases, followed by a decrease in the specific case of Benzotriazole, DEET, Methylindole, and Chlorophene.

Modeling the photodegradation of emerging contaminants in waters by UV radiation and UV/H2O2 system.

Five emerging contaminants (1-H-Benzotriazole, N,N-diethyl-m-toluamide or DEET, Chlorophene, 3-Methylindole, and Nortriptyline HCl), frequently found in surface waters and wastewaters, were selected to be photooxidized in several water matrices. Previous degradation experiments of these compounds individually dissolved in ultra pure water were performed by using UV radiation at 254 nm and the Fentons reagent. These oxidation systems allowed the determination of the quantum yields and the rate constants for the radical reaction between each compound and hydroxyl radicals. Later, the simultaneous photodegradation of mixtures of the selected ECs in several types of water (ultrapure water, reservoir water, and two effluents from WWTPs) was carried out and a kinetic study was conducted. A model is proposed for the ECs elimination, and the theoretically calculated concentrations with this model agreed well with the experimental results obtained, which confirmed that it constitutes an excellent tool to predict the elimination of these compounds in waters.

Investigating PPCP Removal from Wastewater by Powdered Activated Carbon/Ultrafiltration

Powdered activated carbon/ultrafiltration (PAC/UF) hybrid process was investigated for removing from wastewater five pharmaceutical and personal care products (PPCPs): 1-H-benzotriazole, DEET, chlorophene, 3-methylindole and nortriptyline-HCl. Adsorption, UF and PAC/UF experiments were performed, focusing on PPCP adsorption as a function of PPCP characteristics and organic matter (EfOM) competition. Two water matrices and two fine-particle PACs were studied, differing on EfOM nature and concentration and on PAC microporosity. Neutral PPCP uptake by the positively charged, meso- and microporous PACs followed PPCP hydrophobicity expressed by log Kow. The uptake of the positively charged nortriptyline exceeded the expected from log D due to its high aromaticity and the background ions, which partially shielded PAC-nortriptyline electrostatic repulsions. Adsorption capacity depended on PPCP hydrophobicity whereas the kinetics further depended on PPCP charge. Hydrophobic EfOM was preferentially adsorbed and a stronger competitor, particularly for PPCPs with logKow < 2.6. The highly microporous PAC better adsorbed these PPCPs and the hydrophobic EfOM, and it attenuated the EfOM competition. For all waters, PAC had no effect on UF-flux, and it significantly improved PPCP and EfOM removal by PAC/UF over standalone PAC and UF. For all conditions and microcontaminants, PPCP uptake exhibited a sigmoid curve with logKow, with a turning point at 2.2–2.6. In real applications, meso- and highly microporous PACs are recommended, and the dose should target the PPCPs with log Kow < 2.6.

Ozonation of benzotriazole and methylindole: Kinetic modeling, identification of intermediates and reaction mechanisms

The ozonation of 1H-benzotriazole (BZ) and 3-methylindole (ML), two emerging contaminants that are frequently present in aquatic environments, was investigated. The experiments were performed with the contaminants (1μM) dissolved in ultrapure water. The kinetic study led to the determination of the apparent rate constants for the ozonation reactions. In the case of 1H-benzotriazole, these rate constants varied from 20.1 ± 0.4M(-1)s(-1) at pH=3 to 2143 ± 23 M(-1)s(-1) at pH=10. Due to its acidic nature (pKa=8.2), the degree of dissociation of this pollutant was determined at every pH of work, and the specific rate constants of the un-dissociated and dissociated species were evaluated, being the values of these rate constants 20.1 ± 2.0 and 2.0 ± 0.3 × 10(3)M(-1)s(-1), respectively. On the contrary, 3-methylindole does not present acidic nature, and therefore, it can be proposed an average value for its rate constant of 4.90 ± 0.7 × 10(5)M(-1)s(-1) in the whole pH range 3-10. Further experiments were performed to identify the main degradation byproducts (10 mg L(-1) of contaminants, 0.023 gh(-1) of ozone). Up to 8 intermediates formed in the ozonation of 3-methylindole were identified by LC-TOFMS, while 6 intermediates were identified in the ozonation of 1H-benzotriazole. By considering these intermediate compounds, the reaction mechanisms were proposed and discussed. Finally, evaluated rate constants allowed to predict and modeling the oxidation of these micropollutants in general aquatic systems.

The Effectiveness of Single Oxidants and AOPs in the Degradation of Emerging Contaminants in Waters: A Comparison Study

The effectiveness of single oxidants and several AOPs was studied for the degradation of five selected emerging contaminants: Benzotriazole, N,N-diethyl-m-toluamide or DEET, Chlorophene, 3-Methylindole and Nortriptyline HCl. First-order rate constants and half-life times for the degradation of each compound in ultra-pure water were deduced and compared. The AOPs were later applied to the degradation of these ECs present in three real waters: public reservoir water, and two secondary effluents from municipal wastewater plants. The effect of the variables on the ECs elimination was established. Finally, a cost estimation based on the operating costs was established for the degradation of 3-Methylindole by the single oxidants and AOPs tested.

Changes in copper toxicity towards diatom communities with experimental warming

Biological communities in aquatic environments most commonly face multiple stress, where natural and anthropogenic stressors often act jointly. Their interactions are most easily assessed using short cycle organisms such as periphytic diatoms. In this experiment, we analyzed the combined effects of copper exposure and warming on diatom successions over 6 weeks. Natural biofilm collected in winter was left to grow in mesocosms exposed or unexposed to realistic Cu concentrations at four different temperatures. Separate and joint impacts of the two stressors were determined through structural and functional endpoints. Both temperature and copper influenced the biological responses; their interaction, when significant, was always antagonistic. Diatom communities gradually changed with rising temperature. Under copper exposure, the dominant Planothidium lanceolatum was superseded by Achnanthidium exiguum, which accounted for about 70% relative abundance in the warmest conditions (18-23°C). Tolerance to copper was derived from dose-response curves based on photosynthesis inhibition. Cu-induced community tolerance was always found, but it decreased with warming and time. Biodiversity loss associated with lower Cu tolerance under combined Cu exposure and increasing temperatures evidences the major influence of cumulative stressors on aquatic health. These results highlight the crucial interplay between environmental stressors, which are expected to intensify with climate change.

Influence of membrane, pH and water matrix properties on the retention of emerging contaminants by ultrafiltration and nanofiltration

AbstractThe removal of five emerging contaminants (ECs) (1-H-benzotriazole, DEET, chlorophene, 3-methylindole and nortriptyline) dissolved in several water matrices by ultrafiltration and nanofiltration (NF) membranes has been investigated. Pore blocking and cake layer formation probably dominated at the beginning of filtration, whereas cake layer formation was likely the dominant fouling mechanism at later stages. The NF HL membrane was the most appropriate for the removal of the selected ECs, except for benzotriazole, which presented low retention. Therefore, the NF HL membrane is a feasible option for drinking water production and for the purification of not very contaminated secondary effluents for reuse.