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• More ROS production were found during the flood periods in Poyang Lake. • Some refractory components played a critical role in ROS production. • OPLS were used to build a novel predictive model for indicating the spatio-temporal ROS production. • The higher concentrations of ROS in the flood period could speed up the removal of contaminants. Reactive oxygen species (ROS) are omnipresent in natural aquatic environments, and play an important role in biogeochemical cycles. One of the dominant sources of ROS in surface waters was thought to be from dissolved organic matter (DOM) interacting with photochemical process. The properties of DOM were different between the flood and drought periods in lakes; yet, information on how these variations influence ROS photoproduction is unknown. Through a three-year study, the photochemical properties of DOM and the resultant ROS photoproduction between the flood and drought period were determined in the largest freshwater lake in China (Lake Poyang). Results found that quantum yield coefficients of excited triplets (3CDOM*), apparent quantum yields of singlet oxygen (1O 2) and hydroxyl radicals (•OH) were holistically higher in the flood period than those in the drought period. The optical properties of DOM showed that DOM in the flood period featured an allochthonous input, accompanied by higher molecular size (E2/E3), aromatic content (SUVA 254), humification degree (HIX), while DOM in the drought period was mainly internal input. Fourier transform ion cyclotron resonance mass spectrometry (FI-ICR MS) further revealed that some refractory components, such as lignin-like and carboxyl-rich alicyclic molecules (CRAM) presented higher abundance in the flood period, and played the positive impacts on ROS production. Orthogonal partial least squares (OPLS) were used to build novel multivariate predictive models for indicating the spatio-temporal ROS production. Also, the relatively higher steady-state concentrations of 3CDOM* and 1O 2 in the flood period could significantly diminish the half-lives of acetochlor. Considering the photochemical activity of DOM varied considerably at different periods, this study provided a new method to predict ROS production and contributed to a new insight into stage-specific emerging contaminants removing in natural aquatic environments. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The azole fungicide fluconazole has been reported to be persistent in conventional wastewater treatment plants. This study investigated the photodegradation of fluconazole under UV-254 in aqueous solutions. The results revealed that the photodegradation of fluconazole was pH-dependent (2.0–12.0) following the pseudo-first-order kinetics with quantum yield values ranging from 0.023 to 0.090 mol einstein−1, and it underwent a direct and self-sensitized mechanism involving 1O2. The main photodegradation by-products were identified and semi-quantitated. The proposed photodegradation pathway included hydroxylative defluorination reaction. The 72 h-NOEC and 72 h-LOEC values for fluconazole using a freshwater unicellular green alga Pseudokirchneriella subcapitata were 10 μM and 15 μM. Overall, the photodegradation of fluconazole produced a significant decrease in algal toxicity. It also proved that the photodegradation by-products will not present extra toxicity to this alga than fluconazole itself. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: The photocatalytic degradation of two phenolic compounds, p-coumaric acid and caffeic acid, was performed with a suspended mixture of TiO2 and powdered activated carbon (PAC) (at pH=3.4 and 8). Adsorption, direct photolysis and photocatalytic degradation were studied under different pH and UV light sources (sunlight vs. 365nm UV lamps). The potential for reusing this catalyst mixture in sequential photocatalytic runs was examined as well. Quantum yields for the direct photolysis of caffeic acid under solar and artificial 365nm light were calculated (for the first time) as 0.005 and 0.011, respectively. A higher removal rate of contaminants by either adsorption or photocatalysis was obtained at a low pH (pH 4). Furthermore, the addition of PAC increased the removal efficiency of the phenolic compounds. Fast removal of the pollutants from the solution over three sequential runs was achieved only when both TiO2 and PAC were present. This suggests that at medium phenolic concentrations, the presence of PAC as a co-sorbent reduces surface poisoning of the TiO2 catalyst and hence improves photocatalysis degradation of phenolic pollutants. The adsorption equilibrium of caffeic acid or p-coumaric acid on TiO2, PAC and the combined mixture of TiO2 and PAC follows the Langmuir isotherm model. Experiments with PAC TiO2 mixture and olive mill wastewater (anaerobically treated and diluted by a factor of 10) showed higher removal of polyphenols than of chemical oxygen demand (COD). 87% removal of total polyphenols, compared to 58% of COD, was achieved after 24h of exposure to 365nm irradiation (7.6W/m2) in the presence of a suspended mixture of TiO2 and PAC, indicating “self-selectivity” of polyphenols. [Copyright &y& Elsevier]

Abstract: The chemical oxidation of the organophosphorus insecticide chlorfenvinphos, a priority pollutant in aquatic environments, has been conducted in ultrapure water, by means of single degradation agents (ozone and UV radiation), and by the Advanced Oxidation Processes constituted by combinations of these oxidants (O3/H2O2 and UV/H2O2). The influence of the operating variables was discussed, and the degradation rates were evaluated by determining the rate constants for the reactions with ozone (=3.7±0.2Lmol−1 s−1) and OH radicals (k OH=(3.2±0.2)×109 Lmol−1 s−1), as well as the quantum yield for the photodegradation (around 0.1molE−1, depending on the pH). Additionally, the ozonation of chlorfenvinphos in a natural water system (a surface water from a reservoir) was studied. The influence of the operating conditions on the insecticide removal efficiency was established, and the R ct parameter was evaluated. A kinetic model was proposed for the prediction of the elimination rate of chlorfenvinphos in the ozonation process and the results obtained reveal a good agreement between experimental results and predicted values. [Copyright &y& Elsevier]