Modeling carbonate/bicarbonate and nitrate disturbance during secondary effluent disinfection by UV/H2O2 and UV/ozone.

The disinfection of effluents has been considered the main step to inactivate pathogenic organisms to prevent the spread of waterborne diseases. The variation in the matrix composition can lead to the use of inadequate oxidant dose and disturb a correct treatment. The objective of this study was to develop a simple and practical mathematical model to simulate the disturbance of inorganic anions (CO32-/HCO3- and NO3-) during secondary effluent disinfection by UV/H2O2 and UV/O3. The pathogenic agents chosen for this study were total coliforms and E. coli. To build the mathematical model, a modification of the Chick model (referred to as 'Modified Chick Model') was proposed by employing a weighted average in the calculation of the kinetic constant. Both treatments were affected by the presence of the anions. However, with the highest NO3- concentration, less inhibition of disinfection was observed in the UV/H2O2. The use of the arithmetic means to calculate the value of k, as indicated by the Chick model, demonstrates a lesser precision in the prediction of the microorganisms' concentrations. On the other hand, using the Modified Chick Model, a better prediction of the inactivation of the microorganisms was obtained, which can be confirmed by the validation performed.

Synthesis and Characterization of N and Fe-Doped TiO2 Nanoparticles for 2,4-Dimethylaniline Mineralization.

The present study aimed to evaluate the feasibility of developing low-cost N- and Fe-doped TiO2 photocatalysts for investigating the mineralization of 2,4-dimethylaniline (2,4-DMA). With a single anatase phase, the photocatalysts showed high thermal stability with mass losses of less than 2%. The predominant oxidative state is Ti4+, but there is presence of Ti3+ associated with oxygen vacancies. In materials with N, doping was interstitial in the NH3/NH4+ form and for doping with Fe, there was a presence of Fe-Ti bonds (indicating substitutional occupations). With an improved band gap energy from 3.16 eV to 2.82 eV the photoactivity of the photocatalysts was validated with an 18 W UVA lamp (340-415 nm) with a flux of 8.23 × 10-6 Einstein s-1. With a size of only 14.45 nm and a surface area of 84.73 m2 g-1, the photocatalyst doped with 0.0125% Fe mineralized 92% of the 2,4-DMA in just 180 min. While the 3% N photocatalyst with 12.27 nm had similar performance at only 360 min. Factors such as high surface area, mesoporous structure and improved Ebg, and absence of Fe peak in XPS analysis indicate that doping with 0.0125% Fe caused a modification in TiO2 structure.

Photoelectrocatalytic Degradation of Methylene Blue Using ZnO Nanorods Fabricated on Silicon Substrates.

ZnO nanorods were grown on silicon (Si) substrates by two techniques: (i) Chemical Bath Deposition (CBD) and (ii) a CBD seed layer combined with Carbothermal Reduction Vapor Phase Transport (CTR-VPT). The structured ZnO nanorods were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and contact angle measurments. The photoelectrochemical property of ZnO nanorods were analyzed by linear voltammetry under UV-ABC light excitation. Using the ZnO nanorod samples as photoanodes, the removal of methylene blue (MB) as a representative organic compound was studied by the photoelectrocatalytic (PEC) technique applying a potential (E) of 0.6 V. For comparison purposes, experiments were performed under the same conditions using photocatalysis (PC), direct photolysis and using samples of pure Si (support material) as working electrodes in PEC. XRD analyses of ZnO prepared by both methods showed the expected ZnO wurtzite phase and a preferred c-axial orientation in the growth of the nanorods. The presence of ZnO was further confirmed by XPS and contact angle measurements showed that ZnO grown by CBD (ZnO/CBD) had a slightly hydrophobic behavior while ZnO grown by CTR-VPT (ZnO/CTR-VPT) is hydrophilic. Both ZnO sample types were shown to be photoactive, with ZnO/CBD showing higher resultant photocurrent compared to ZnO/CTRVPT. For the degradation of MB 53% of the compound was removed using ZnO/CBD as a working electrode, while using the ZnO/CTR-VPT electrode led to a removal of 43% of MB. However, direct photolysis alone removed 39% of the MB. The lower removal of MB using ZnO/CTR-VPT samples was related to surface dissociation during the degradation process. The results show that ZnO nanorods prepared by the CBD techique are a promising photoelectrode for PEC applications. Our data also indicate that CTR-VPT-grown nanorods produce uniform nanorod arrays, but this uniform nanostructure deposit does not lead to any increase in PEC activity.

Identification of intermediates, acute toxicity removal, and kinetics investigation to the Ametryn treatment by direct photolysis (UV254), UV254/H2O2, Fenton, and photo-Fenton processes.

This paper reports the degradation of 10 mg L-1 Ametryn solution with different advanced oxidation processes and by ultraviolet (UV254) irradiation alone with the main objective of reducing acute toxicity and increase biodegradability. The investigated factors included Fe2+ and H2O2 concentrations. The effectiveness of the UV254 and UV254/H2O2 processes were investigated using a low-pressure mercury UV lamp (254 nm). Photo-Fenton process was explored using a blacklight blue lamp (BLB, λ = 365 nm). The UV254 irradiation process achieved complete degradation of Ametryn solution after 60 min. The degradation time of Ametryn was greatly improved by the addition of H2O2. It is worth pointing out that a high rate of Ametryn removal was attained even at low concentrations of H2O2. The kinetic constant of the reaction between Ametryn and HO● for UV254/H2O2 was 3.53 × 108 L mol-1 s-1. The complete Ametryn degradation by the Fenton and photo-Fenton processes was observed following 10 min of reaction for various combinations of Fe2+ and H2O2 under investigation. Working with the highest concentration (150 mg L-1 H2O2 and 10 mg L-1 Fe2+), around 30 and 70% of TOC removal were reached within 120 min of treatment by Fenton and photo-Fenton processes, respectively. Although it did not obtain complete mineralization, the intermediates formed in the degradation processes were hydroxylated and did not promote acute toxicity of Vibrio fischeri. Furthermore, a substantial improvement of biodegradability was obtained for all studied processes.

H2O2-assisted photoelectrocatalytic degradation of Mitoxantrone using CuO nanostructured films: Identification of by-products and toxicity.

CuO nanostructured thin films supported on silicon with 6.5 cm2 area (geometric area greater than the studies reported in the literature) were synthesized by a chemical bath deposition technique. The electrodes were characterized by MEV, XRD, XPS, contact angle, cyclic voltammetry and electrochemical impedance spectroscopy analyses. To evaluate the photoelectrochemical properties of the CuO films, photocurrent-voltage measurements were performed using linear voltammetry. The catalytic activities of CuO nanostructures were evaluated by monitoring photodegradation of Mitoxantrone (MTX) under UV-A light irradiation. The method of photoelectrocatalysis (PEC), applying a voltage of 1.5 V and assisted by adding H2O2, was undertaken. To the best of our knowledge, no studies on the degradation of anticancer agents using PEC process have been found in the literature. For comparison purposes, experiments were performed under the same conditions by assisted photocatalysis (PC) with H2O2 and direct photolysis. CuO deposits consist of a needle-like morphology. The presence of CuO in the tenorite phase was evidenced by XRD and the XPS spectra showed the presence of copper(II) oxide. The increase in current under illumination shows that CuO exhibits photoactivity. The PEC system showed a 75% level of MTX degradation, while the level achieved using PC was 50%. Under UV-A light alone only 3% removal was obtained after 180 min. Up to 10 by-products were identified by chromatography-mass spectrometry (LC-MS) with m/z values ranging between 521 and 285 and a plausible degradation route has been proposed. It is worth mentioning that 9 by-products identified in this work, were not found in the literature in other studies of degradation or products generated as metabolites. The toxicity tests of MTX before and after PEC treatment with Artemia Salina and Allium cepa showed a decrease in the acute toxicity of the medium as the antineoplastic was degraded.

Optimization of nimesulide oxidation via a UV-ABC/H2O2 treatment process: Degradation products, ecotoxicological effects, and their dependence on the water matrix.

Nimesulide (Nim) degradation in ultrapure water (UW) and municipal sewage (MS) via UV-ABC/H2O2 was investigated. The variables included in the experimental design were time, initial Nim, and initial H2O2 concentrations. Resulting decreases in Nim concentration (monitored by high performance liquid chromatography (HPLC) using a photodiode array detector operating at a maximum UV absorbance of 300 nm), mineralization (from total organic carbon (TOC) measurements), and ecotoxicity (assays employing the bioindicators Daphnia similis, Artemia salina, and Allium cepa) were also studied. Degradation rates of 90% or higher were found for 15-20 min reaction times, employing combinations of [H2O2] = 50-150 mg L-1 and [Nim] = 8.5-15 mg L-1 prepared with MS. Mineralization rates of 70% and higher were attained within 60 min of reaction for [Nim] = 15 mg L-1 prepared in MS with [H2O2] = 100 mg L-1. Nim by-products were detected and possible degradation pathways proposed. Ecotoxicity evaluation using A. salina, D. similis, and A. cepa revealed that the treated samples had significantly lower toxicity. Exposure to treated samples resulted in survival rates of 79% for A. salina and over 90% for D. similis. No root growth inhibition was observed in A. cepa exposed to treated samples, whereas exposure to untreated samples inhibited root growth by 60%. Statistical analysis revealed elimination of cytotoxicity and reduction of genotoxicity against A. cepa. The results showed that the UV-ABC/H2O2 process can be employed as a pre- or post-treatment method to remove Nim from contaminated wastewater.

Application of Fenton, photo-Fenton, solar photo-Fenton, and UV/H2O2 to degradation of the antineoplastic agent mitoxantrone and toxicological evaluation.

In the present study, selected advanced oxidation processes (AOPs)-namely, photo-Fenton (with Fe(2+), Fe(3+), and potassium ferrioxalate-FeOx-as iron sources), solar photo-Fenton, Fenton, and UV/H2O2-were investigated for degradation of the antineoplastic drug mitoxantrone (MTX), frequently used to treat metastatic breast cancer, skin cancer, and acute leukemia. The results showed that photo-Fenton processes employing Fe(III) and FeOx and the UV/H2O2 process were most efficient for mineralizing MTX, with 77, 82, and 90% of total organic carbon removal, respectively. MTX probably forms a complex with Fe(III), as demonstrated by voltammetric and spectrophotometric measurements. Spectrophotometric titrations suggested that the complex has a 2:1 Fe(3+):MTX stoichiometric ratio and a complexation constant (K) of 1.47 × 10(4) M(-1), indicating high MTX affinity for Fe(3+). Complexation partially inhibits the involvement of iron ions and hence the degradation of MTX during photo-Fenton. The UV/H2O2 process is usually slower than the photo-Fenton process, but, in this study, the UV/H2O2 process proved to be more efficient due to complexing of MTX with Fe(III). The drug exhibited no cytotoxicity against NIH/3T3 mouse embryonic fibroblast cells when oxidized by UV/H2O2 or by UV/H2O2/FeOx at the concentrations tested.