The effluents of some pulp and paper processes are potentially pollutant, because of their large volume and their refractory nature. Biological processes generally are not capable to remove these compounds. Advanced Oxidation Processes (AOP) are characterized by the capability of exploiting the high reactivity of HO• radicals. AOP can produce a total mineralization, transforming recalcitrant compounds into inorganic substances (CO 2 and H 2 O 2), or partial mineralization, transforming them into more biodegradable substances. The high reactivity and low selectivity of these radicals are useful attributes that that make these processes in promising technologies. Due to the differences between pulping processes, the effluents from the various processes and operations of such industries also differ from each other, so that some oxidative processes should be combined to improve the removal efficiency. For the effective oxidation of refractory organic compounds, hydroxyl radicals should be generated continuously in situ due to its chemical instability. Generation of HO• is commonly accelerated by combining oxidizing agents. Among these treatments, UV radiation plus hydrogen peroxide (UV/H 2 O 2), Fenton's reagent (H 2 O 2 /Fe +2), photo-Fenton (UV/H 2 O 2 /Fe +2), and ozone in different combinations (O 3 /UV; O 3 /H 2 O 2) are considered to be effective for the oxidation of effluents from pulp and paper industries.

This work proposes a kinetic model for the reactions involved in the heterogeneous copper-based Fenton-type oxidation of mixed recalcitrant compounds in a real industrial effluent from the alkaline sulfite treatment of wood. This kind of treatment is unusual in this industry due to the complexity of the effluents and the high costs involved in total mineralization of the organic matter. Nevertheless, conversion of recalcitrant to degradable compounds and catalyst recovery can make the difference. The complexity of the effluent and the great number of compounds formed as intermediates, make extremely difficult the identification and quantification of the individual reactions that occur during oxidation. To solve this drawback TOC parameter was used as a representative measurement. To verify the level of TOC degradation produced by the heterogeneous catalysis reaction, experiences of homogeneous catalysis and adsorption were accomplished. The studied temperature range was 45-80 °C. A "two-step" kinetic model was applied to TOC reduction in heterogeneous and homogeneous oxidations, admitting two sequential steps of oxidation: a first fast stage ("seconds stage") followed by a slow one ("minutes stages"). Kinetic constants were obtained for both processes and activation energies were also determined for the "minutes stage" step (33.17 kJ/mol and 15.13 kJ/mol, respectively). Homogeneous catalysis studies confirm mass transfer limitations in heterogeneous oxidations. Experiences of adsorption of organic matter on CuO/γ-Al 2 O 3 catalyst demonstrated that this phenomenon is exothermic and cannot be neglected. The activation energy of adsorption was determined as 7.32 kJ/mol. Catalysts were characterized through SEM, EDS, XRD, FTIR, and TGA. Graphical Abstract

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The differences between a biorefinery and an oil refinery are determined by the higher oxygen content of the biorefinery's biomass, its high degree of functionalization, its low thermal stability, its polar components, which are mostly acidic, its highly heterogeneous structure, and its quality variation as result of genotypic and phenotypic characteristics. Levulinic acid (LA) is one of the main high value‐added chemicals that can be produced from lignocellulosic biomass as raw material. The main challenges for the conversion of lignocellulosic biomass to levulinic acid are related to the improvement of the technologies to obtain a pure and cost‐competitive product, the design and use of efficient heterogeneous catalysts, and the improvements in the selectivity and useful life of the catalyst. This is an up‐to‐date review of the state of knowledge about the heterogeneous catalytic conversion of biomass into LA, addressing the technical hurdles that impede the attainment of high yields. This work outlines the chemistry of LA synthesis and discusses in detail the influence of the lignocellulosic raw material, reaction time, temperature, solvent according to the chemical pathway, and efficiency of the chosen Lewis and Brønsted solid acid catalysts. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Because of their chemical complexity, industrial chemi-mechanical pulping effluents are evaporated and burned, in spite of the high associated cost involved in these processes. The aim of this study was to remove recalcitrant compounds from this kind of wastewater using a Fenton-type treatment. The main parameters involved in the process and their influence on the results were determined. Homemade catalysts based on CuO, Fe 2 O 3 , NiO, and ZnO, supported on g-Al 2 O 3 have been tested for catalytic oxidation, and the CuO/g-Al 2 O 3 catalysts showed the greatest effect on total organic carbon (TOC) reduction (52.7%). A series of two-level factorial experiments was subsequently applied to evaluate the most favorable range of conditions for CuO/g-Al 2 O 3 application. The studied variables were hydrogen peroxide concentration ([H 2 O 2 ], g/L), active phase content (metal oxide supported on alumina,%), mass of catalyst (metal oxide/alumina system, g), and reaction temperature (°C). The highest reduction of all parameters was obtained at the superior level of all variables with CuO/g-Al 2 O 3 , achieving reductions of chemical oxygen demand (COD) and TOC between 40 and 50%. Increasing catalyst mass did not produce additional benefit. This variable has a significant effect only on the reduction of aromatic compounds. At its low level, reduction in aromatic content exceeded 80%. Color reduction was influenced only by temperature (maximum reduction of 90%).