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Sunscreen agents are chemical compounds widely used nowadays for skin protection from UV sunlight. Recently, their ubiquitous occurrence in aquatic systems has been evidenced, which poses a high risk for the environment and human health as they are associated with endocrine disrupting activity, reproductive toxicity, and genotoxicity. In this work, the feasibility of an economically and environmentally friendly catalytic system based on the thermally modified natural magnetite and hydrogen peroxide (Fe 3 O 4 -R400/H 2 O 2), has been evaluated for the degradation of two representative sunscreen agents: benzophenone-3 (BP-3) and 4-aminobenzoic acid (PABA) in wastewater. The experiments were conducted under circumneutral pH (pH 0 = 5), with temperature control (25 °C). Both compounds (500 μg L−1) were successfully removed from water by using a relatively low catalyst concentration (0.5 g L−1) and the theoretical stoichiometric H 2 O 2 dose for their complete oxidation (∼2.3 mg L−1). Afterwards, a complete operating condition study was performed with BP-3, given its predominant occurrence in fresh waters, analysing the influence of H 2 O 2 dose (1.2–4.6 mg L−1), catalyst concentration (0.1–0.5 g L−1), and temperature (25–45 °C). From the evolution of the identified by-products, a reaction pathway was proposed according to which oxidation of BP-3 gives rise to several aromatic intermediates, which finally evolve to short-chain organic acids. The generation of such aromatic by-products led to a considerably ecotoxicity increase in the initial stages of the reaction, but non-toxic effluents were ultimately achieved. Notably, the mineralization yield reached was above 60%. As a proof of concept, the feasibility of the system was finally demonstrated in real water matrices (WWTP effluent and surface water). [Display omitted] • The Fe 3 O 4 -R400/H 2 O 2 system was effective for the removal of sunscreen agents. • The pollutants were highly mineralized (∼60%), yielding short-chain acids. • A reaction pathway for BP-3 oxidation was proposed. • Non-toxic effluents were obtained despite a slight initial ecotoxicity increase. • The feasibility of the process was demonstrated in different water matrices. [ABSTRACT FROM AUTHOR]

This work explores the modification of naturally occurring magnetite by controlled oxidation (200–400 °C, air atmosphere) and reduction (300–600 °C, H2 atmosphere) treatments with the aim of boosting its activity in CWPO. The resulting materials were fully characterized by XRD, XPS, TGA, TPR, SEM, and magnetization measurements, allowing to confirm the development of core-shell type structures. The magnetite core of the solid remained unchanged upon the treatment whereas the Fe(II)/Fe(III) ratio of the shell was modified (e.g. 0.42, 0.11 and 0.63 values were calculated for pristine Fe3O4, Fe3O4-O400, and Fe3O4-R400, respectively). The performance of the catalysts was tested in the CWPO of sulfamethoxazole (SMX) (5 mg L−1) under ambient conditions and circumneutral pH (pH0 = 5), using the stoichiometric dose of H2O2 (25 mg L−1) and a catalyst load of 1 g L−1. The key role of the ferrous species on the mineral shell was evidenced. Whereas the oxidation of magnetite led to significantly slower degradation rates of the pollutant, its reduction gave rise to a dramatic increase, achieving the complete removal of SMX in 1.5 h reaction time with the optimum catalyst (Fe3O4-R400) compared to the 3.5 h required with the pristine mineral. A reaction mechanism was proposed for SMX degradation, and a kinetic equation based on the Eley-Rideal model was accordingly developed. This model successfully fitted the experimental results. The stability of Fe3O4-R400 was evaluated upon five sequential runs. Finally, the versatility of the catalytic system was proved in real environmentally relevant water matrices. [ABSTRACT FROM AUTHOR]

BACKGROUND The breakdown of imidazolium ionic liquids ( ILs) by Fenton oxidation has been demonstrated, but using unaffordable doses of hydrogen peroxide ( H2O2). The literature studies so far do not report on the evolution of total organic carbon ( TOC) and ecotoxicity. Therefore, the potential application of the process for the degradation of ILs still remains an open question. This work investigates the feasibility of the Fenton process for the treatment of aqueous effluents containing imidazolium-based ILs of different structures, represented by the length of the alkyl chain and the nature of the anion. Special attention is paid to the evolution of the ecotoxicity and the consumption of H2O2 as a critical issue for the economy of the process. The experiments were performed at 70 °C. RESULTS With the stoichiometric H2O2 dose, the complete conversion of the starting imidazolium-based ILs was achieved in less than 5 min, at 70°C, with 60% of TOC reduction after 4 h, except in the [C4mim][ CH3CO2] case, where iron precipitation was observed, thus inhibiting its catalytic action. Low ecotoxicity effluents were obtained at the stoichiometric H2O2 dose, even in the cases of the highly ecotoxic ILs of long alkyl chain with chloride anion. CONCLUSION Fenton oxidation is shown to be a promising solution for the degradation of imidazolium-based ILs in water, allowing deep detoxification with the stoichiometric H2O2 dose. © 2014 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

This work explores the potential application of naturally-occurring minerals as inexpensive catalysts in heterogeneous Fenton, namely catalytic wet peroxide oxidation (CWPO). The availability, low cost and environmentally friendly character of those materials make them interesting candidates for such application. The performance of magnetite, hematite and ilmenite as CWPO catalysts has been tested under different working conditions, which include temperature (25–90 °C), H 2 O 2 dose (250–1000 mg L −1 ) and catalyst concentration (1–4 g L −1 ). The operating temperature plays a key role on the rate of H 2 O 2 decomposition so that with magnetite H 2 O 2 conversion after 4 h increased from 8 to 99% by increasing the temperature from 25 to 90 °C. Based on the reaction mechanism proposed, a kinetic model was developed which successfully described the experimental results on H 2 O 2 decomposition. The catalytic performance of the minerals tested at temperatures above the ambient was demonstrated using phenol (100 mg L −1 ) as target pollutant. Unprecedented efficiencies of H 2 O 2 consumption, higher than 80% were achieved, allowing high oxidation and mineralization, i.e. complete phenol conversion and almost 80% TOC reduction at 75 °C with a catalyst loading of 2 g L −1 and the theoretical stoichiometric amount of H 2 O 2 for complete mineralization of phenol (500 mg L −1 ). Magnetite is particularly attractive, since it showed the highest activity and can be easily separated from the liquid phase given its magnetic properties. All the minerals tested suffered low iron leaching and magnetite and hematite showed a good reusability upon three consecutive runs. However, in this case long-term durability is not a crucial issue, given the availability and low cost of these minerals. [ABSTRACT FROM AUTHOR]

The production and application of ionic liquids (ILs) is often associated with the formation of aqueous effluents. Due to the well-known toxicity and poor biodegradability of those compounds, effective treatments for their removal from aqueous solutions are required. In this work, the Fenton oxidation methodology under optimum operating conditions (50 mg L −1 Fe 3+ , stoichiometric dose of H 2 O 2 , 70 °C and pH 0 = 3) was investigated in eleven different ILs, based in the imidazolium, phosphonium, quaternary ammonium, pyridinium and cholinium families, conjugated with various inorganic and organic anions such as chloride, cyanoborate, cyanamide, thiocyanate, dimethylphosphate and tosylate. The efficacy of the process was evaluated by the analysis of the chemical oxygen demand (COD), total organic carbon (TOC), the acids formed by ILs oxidation and the toxicity of the non-treated and treated aqueous effluents towards the Vibrio fischeri bacteria. It was possible to identify the main compounds produced upon Fenton oxidation in the final aqueous effluents (acetic, oxalic and formic acids) and the results seem to suggest that the Fenton oxidation is a good degradation methodology for most of the ILs tested, achieving TOC conversions in the range of 40–80% and 30–40% for aromatic and aliphatic ILs, respectively. Furthermore, non-toxic effluents were obtained at the end of the treatment for all the ILs investigated with the exception of the cyano-based ones due to the release of highly toxic cyanide species to the aqueous medium. [ABSTRACT FROM AUTHOR]

Fenton oxidation has proved to be an efficient treatment for the degradation of ionic liquids (ILs) of different families viz. imidazolium, pyridinium, ammonium and phosphonium, in water. The intensification of the process, defined as the improvement on the efficiency of H 2 O 2 consumption, by increasing the temperature is necessary to avoid high reaction times and the need of large excess of H 2 O 2 . In this work, temperatures within the range of 70–90 °C have been used, which allowed an effective breakdown of the ILs tested (1 g L −1 initial concentration) with the stoichiometric amount of H 2 O 2 and a relatively low Fe 3+ dose (50 mg L −1 ). Under these conditions conversion of the ILs was achieved in less than 10 min, with TOC reductions higher than 60% upon 4 h reaction time, except for the phosphonium IL. The remaining TOC corresponded mainly to short-chain organic acids. The treatment reduced substantially the ecotoxicity up to final values below 0.01 TU in most cases and a significant improvement of the biodegradability was achieved. Upon Fenton oxidation of the four ILs tested hydroxylated compounds of higher molecular weight than the starting ILs, fragments of ILs partially oxidized and short-chain organic acids were identified as reaction by-products. Reaction pathways are proposed. [ABSTRACT FROM AUTHOR]

Highlights: [•] The intensified Fenton process represents a cost-effective alternative for sawmill wastewater treatment. [•] Increasing temperature to 120°C and feeding H2O2 in 3 additions improved the H2O2 consumption efficiency. [•] High COD (≈80%) and TOC (≈70%) removal were achieved after 1h reaction time. [•] Fungicides were completely removed obtaining short-chain organic acids as main products. [ABSTRACT FROM AUTHOR]

This work aims at evaluating the fate of microplastics (MPs) along Fenton oxidation. For such goal, realistic MPs (150–250 μm) of five representative polymer types (PET, PE, PVC, PP and EPS) were obtained from commercial plastic products by cryogenic milling. Experiments (7.5 h) were performed under relatively severe operating conditions: T = 80 °C; pH 0 = 3; [H 2 O 2 ] 0 = 1000 mgL−1 (15 doses, 1 every 0.5 h); [Fe3+] 0 = 10 mgL−1 (5 doses, 1 every 1.5 h). Slight MPs weight losses (∼10%) were achieved after Fenton oxidation regardless the MP nature. Nevertheless, oxidation yield clearly increased with decreasing the particle size given their higher exposed surface area (up to 20% weight loss with 20–50 μm EPS MPs). Clearly, MPs suffered important changes in their surface due to the introduction of oxygenated groups, which made them more acidic and hydrophilic. Furthermore, MPs progressively reduced their size. In fact, they can be completely oxidized to CO 2 , as demonstrated in the oxidation of PS nanoplastics (140 nm), where 70% mineralization was achieved. The nature of the plastic particles had a relevant impact on its overall oxidation, being more prone to be oxidized those polymers which contain aromatic rings in their structures (EPS and PET) compared to those formed by alkane chains (PE, PP and PVC). In the latter, the presence of substituents also reduced their oxidation potential. Remarkably, possible leachates released along reaction were more quickly oxidized than the MPs/NPs, so it can be assumed that these dissolved compounds would be completely removed once the solid particles are eliminated. Notably, the leachates obtained upon MPs oxidation were more biodegradable than the released from the fresh solids. All this knowledge is crucial for the understanding of MPs oxidation by the Fenton process and opens the door for the design and optimization of this technology either for water treatment or for analytical purposes (MPs isolation). [Display omitted] • Oxidation reaction proceeds from the surface to the core of plastic particles. • MPs suffered physical alterations and chemical changes along Fenton oxidation. • MPs decreased their size upon oxidation, eventually leading to their mineralization. • MPs bearing aromatic rings showed higher oxidation yields than the alkane-based MPs. • Dissolved leachates generated along the treatment did not inhibit bacterial growth. [ABSTRACT FROM AUTHOR]

The feasibility of catalytic wet air oxidation, intensified homogeneous Fenton and heterogeneous Photo-Fenton systems for the treatment of real hospital wastewater has been investigated. Wastewater samples were collected from a hospital sewer, during a weekly monitoring program, and fully characterized. Up to seventy-nine pharmaceuticals, including mostly parent compounds and some of their transformation products, were analyzed. Catalytic wet air oxidation allowed the complete removal of several pharmaceutical groups, but it did not allow to eliminate analgesics/anti-inflammatories and antibiotics, whose average removal was around 85%. Intensified Fenton oxidation was the most efficient process for all the drugs removal with an almost complete reduction of the initial pharmaceutical load (99.8%). The heterogeneous Photo-Fenton system reached a 94.5% reduction of the initial pharmaceutical load. The environmental risk of the treated samples by the hazard quotient (HQ) method was also evaluated. Fenton oxidation was the most effective system with a final ∑HQ of 5.4. Catalytic wet air oxidation and Photo-Fenton systems achieved total ∑HQ values of 895 and 88, respectively. This fact was related to the presence of refractory antibiotics in the treated catalytic wet air oxidation samples. On the opposite, the Photo-Fenton system provided the elimination of most pharmaceutical pollutants that pose a high environmental risk such as antibiotics. Simplified cost estimation was finally performed as a preliminary approach of the economy of the three oxidation processes for the hospital wastewater treatment. [Display omitted] • Seventy-nine pharmaceuticals were identified in real hospital wastewater. • CWAO, Intensified Fenton and heterogeneous Photo-Fenton technologies were tested for the treatment of hospital wastewater. • Intensified Fenton oxidation achieved the best performance for the reduction of pharmaceutical compounds. • Remaining antibiotics in the treated effluents revealed a significant impact on the environmental risk assessment. • The operating costs are significantly increased for the heterogeneous catalytic systems. [ABSTRACT FROM AUTHOR]