Intensification strategies for thermal H2O2-based advanced oxidation processes: Current trends and future perspectives

H2O2-based advanced oxidation technologies, commonly Fenton process or Catalytic Wet Peroxide Oxidation (CWPO), have been widely studied and applied over the past decades for wastewater treatment due to their ability to generate highly oxidizing species, HO• and HOO• radicals, along with a low selectivity which allow the degradation of a wide range of pollutants . Nonetheless, these technologies present some limitations. In the case of Fenton, the requirement of acidic media (pH: 3), the loss of catalyst at the end of reaction because it is dissolved, and the catalyst inactivation caused by certain reaction intermediates (i.e. oxalic acid) that forms complexes compromising its efficiency. For CWPO, the main drawbacks in this heterogeneous process are mainly associated to the relative low activity and stability of the catalysts employed. All these shortcomings can be solved through process intensification, which generally involves in Fenton and CWPO increasing the temperature or the application of an external radiation, being the most interesting ones UV–vis radiation (photo-assisted technologies), and microwave radiation, which inherently presents the advantages of working at high temperature. This paper gathers the most recent advances explored in thermal-intensified H2O2–based advanced oxidation technologies, summarizing the main results obtained for each intensification strategy and outlining where future efforts should be focuse

Improved wet peroxide oxidation strategies for the treatment of chlorophenols

Different advanced oxidation strategies have been investigated for the treatment of chlorophenols in aqueous phase with the aim of improving the removal efficiency in terms of mineralization, remanent by-products and kinetics. Those strategies were homogeneous Fenton-like oxidation and CWPO with two different own-prepared FexOy/γ-Al2O3 catalysts. The intensification of the process by increasing the temperature has been also evaluated. CWPO of chlorophenols with those catalysts has proved to be more efficient than homogeneous Fenton-like oxidation due to a lower rate of H2O2 decomposition allowing a higher availability of hydroxyl radicals along the course of reaction. Increasing the temperature clearly improved the oxidation rate and mineralization degree of both homogeneous Fenton-like oxidation and CWPO, achieving almost 90% TOC reduction after 1h at stoichiometric H2O2 dose, 100mgL-1 initial chlorophenol concentration, 1gL-1 Fe3O4/γ-Al2O3 catalyst, pH 3 and 90°C temperature. Both FexOy/γ-Al2O3 catalysts suffered fairly low iron leaching (<5%) and a remarkable stability in a three-cycles test with 2,4,6-TCP. The use of the magnetic catalyst is preferable due to its easy separation and recovery from the liquid phase by a magnet. Its magnetic properties remained unchanged after use in CWPOThis research has been supported by the Spanish MICINN through the projects CTQ2008-03988 and CTQ2010-14807 and by the CM through the project S-2009/AMB-1588. M. Munoz thanks the Spanish Ministry of Education for a FPU research gran

Continuous hydrogen production from liquid-phase formic acid dehydrogenation over Pd/AC catalysts: a kinetic study

Hydrogen production using formic acid (FA) as renewable carrier has been investigated in a fixed bed reactor packed with a commercial Pd/AC catalyst. For the first time, both FA disappearance and evolved gas flow rate have been monitored upon space-time, enabling the elucidation of the FA reaction pathway and the development of a kinetic model that accounts for catalyst deactivation. Nearly complete FA conversion and a production of 10 mL min of hydrogen gas were achieved under the following operating conditions: C and τ = 66.7 g CAT 1 h L FA,0 = 1 M, T = 45 ºC . The reaction was found not to be controlled the mass transfer limitations. The kinetic model reveals a first order with respect to FA concentration, with FA disappearing through dehydrogenation into hydrogen and CO 1 2 36.7 kJ mol 1 (E a = 53.6 kJ mol ) as well as sorption onto the catalyst surface without reaction (E a = ). The catalyst deactivation is attributed to the accumulation of reaction species, including FA/ HCOO- (reversibly sorbed) and CO (irreversibly chemisorbed), on the Pd active sites and the progressive decrease in the Pd 2+ /Pd 0 ratioTED2021-130312B-I0

Application of catalytic wet peroxide oxidation for sunscreen agents breakdown

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 (Fe3O4-R400/H2O2), 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 (pH0 = 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 H2O2 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 H2O2 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)PID2019-105079RB-I00, P2018/EMT-434

Catalytic hydrodehalogenation of the flame retardant tetrabromobisphenol A by alumina-supported Pd, Rh and Pt catalysts

Tetrabromobisphenol A (TBBPA) is one of the most used BFRs, being characterized by a strong persistence and leading to negative effects on both the environment and human health. The aim of this work is to evaluate the feasibility of aqueous-phase catalytic hydrodehalogenation (HDH) for the fast and environmentally-friendly degradation of the brominated flame retardant TBBPA. Pd, Rh, and Pt on alumina commercial catalysts (1% wt.) were tested and reactions were performed under ambient operating conditions. TBBPA (1 mg L−1) was completely removed in short reaction times ( 95%) in 15 min using Pd/Al2O3. Nevertheless, employing Rh and Pt alumina-supported catalysts debromination of TBBPA increased progressively requiring much longer times and only 83% and 78% debromination yields were achieved after 2 h reaction, respectively. Bisphenol A (BPA), a well-known endocrine disruptor, was generated as reaction intermediate but it was further hydrogenated with both Pd and Rh catalysts, whereas it remained as reaction product with the Pt catalyst. A series reaction pathway considering both hydrodebromination and hydrogenation steps was proposed based on the obtained results. The experimental data obtained with the Pd/Al2O3 catalyst were successfully described by a pseudo-first order kinetic model, obtaining an apparent activation energy of 36 kJ mol−1. Notably, this catalyst showed a reasonable stability after three consecutive HDH run

Treatment of real winery wastewater by wet oxidation at mild temperature

This study explores the treatment of high-strength real winery wastewater (COD0 ≈ 35 g/L, TOC0 ≈ 11 g/L) by wet oxidation processes. Wet air oxidation (WAO), catalytic wet air oxidation (CWAO), H 2O2-promoted CWAO, wet peroxide oxidation (WPO) and catalytic wet peroxide oxidation (CWPO) were the options tested using different carbon-based catalysts, viz. activated carbon, carbon black and graphite. Their suitability was analyzed in terms of polyphenol, chemical oxygen demand (COD) and total organic carbon (TOC) abatement upon 4 h reaction time. The results showed that hydrogen peroxide was the unique oxidant capable of achieving an effective reduction of the organic load. The graphite tested was the most active catalyst, most probably due in great part to its Fe content (0.4 wt.%), resistant to leaching. CWPO with that graphite was tested at different conditions following the evolution of COD, TOC and ecotoxicity. The best results were obtained by using graphite at 5 g/L, the original pH of the wastewater (3.8), 125 °C and the stoichiometric amount of hydrogen peroxide distributed in stepwise additions. Under those conditions, 80% COD and TOC removals with 85% of hydrogen peroxide efficiency were achieved after 4 h reaction time, giving rise to colorless effluents of very low Microtox ecotoxicityThe authors wish to thank the Spanish MICINN for the financial support through the projects CTQ2008-03988/PPQ and CTQ2010-14807. The Comunidad Autónoma de Madrid is also gratefully acknowledged for the financial support through the project S2009/AMB-158

Strategies for the quantification and characterization of nanoplastics in AOPs research

There is a growing interest in developing new targeted degradation technologies for the removal of micro- and nanoplastics (NPs) in water, corresponding to increased public concerns regarding their potential negative impacts on urban water systems, and consequently on human life quality. Recently, Advanced Oxidation Processes (AOPs) have been proposed as promising treatment alternatives for effective degradation of NPs in water. However, the selection of appropriate analytical methods for monitoring these oxidation tests remains a challenge. Herein, the feasibility of different characterization strategies for monitoring the evolution of NPs in water upon oxidation tests was systematically studied using polystyrene (PS) NPs of different particle sizes (D 0 =140, 252, 460, and 909 nm) as model plastic pollutants. To quantify NPs in water, Total Organic Carbon (TOC), Chemical Oxygen Demand (COD) and turbidity measurements were assessed. Moreover, turbidity was correlated to the particle size and PS NPs concentration by developing a response surface. Among the analytical techniques employed to characterize the solid particles, transmission electronic microscopy (TEM) was used to evaluate morphology and particle size. Alternatively, the viability of Dynamic Light Scattering (DLS), Nanoparticle Tracking Analysis (NTA) and Atomic Force Microscopy (AFM) to determine particle size is discussed. Chemical surface modifications were explored by Fourier-Transform Infrared Spectroscopy (FTIR). As a proof of concept, the degradation of PS NPs in water upon photo-Fenton oxidation was investigated at ambient conditions and fully characterized using the mentioned techniquesTED2021-131380B-C21, PID2019-105079RB-I00, PID2022-139063OB-I00, Horizon Europe 101062665, TED2021-129937B-I0

Graphite and carbon black materials as catalysts for wet peroxide oxidation

This study explores the application of non-porous carbon materials, two graphites (G-F, G-S) and two carbon blacks (CB-V and CB-C) as catalysts for wet peroxide oxidation (CWPO). The activity, efficiency and stability of these carbon materials have been evaluated using phenol as target compound. The catalyst screening experiments were carried out batch-wise at CPhenol,0=1g/L, CH2O2,0=5g/L, Ccat=2.5g/L, T=80°C and pH0=3.5. The results allow concluding that CB-C was the most stable catalyst, although it showed a lower oxidation and mineralization activity than G-S and CB-V. Increasing the temperature up to 90°C allowed complete phenol conversion and around 70% TOC reduction with 100% efficiency of hydrogen peroxide consumption upon 20h reaction time at 5g/L CB-C load. As a consequence of the initial oxidation of the carbon surface, the electrochemical properties of CB-C were favorably changed upon CWPO and its catalytic performance was improved from the first to the second use and then maintained upon successive applications in a five-cycle testThe authors wish to thank the Spanish MICINN for the financial support through the projects CTQ2008-03988/PPQ and CTQ2010-14807. The Comunidad Autónoma de Madrid is also gratefully acknowledged for the financial support through the project S2009/AMB-158