Heterogeneous fenton-type treatment of an industrial effluent from forest biomass processing

PAOLA MASSA; FERNANDO.E. FELISSIA; ROSA J. FENOGLIO; MARÍA C. AREA; LAURA G. COVINICH

Congreso; 5º Environmental Applications of Advanced Oxidation Processes; 2017

Alkaline sulfite treatment of wood in chemimechanical pulping do not have a chemical recovery system, and diluted spent liquors are generally treated in the effluent system. However, several of its components are refractory to typical microbiological degradation (i.e. aromatic derivatives from wood extractives and labile lignin fractions) and require more suitable technologies [1]. Advanced Oxidation Processes (AOP) have emerged as promisory treatment alternatives [1-2]. So far, among non-irradiated AOPs studies of industrial streams, those using Fenton type oxidation are scarce and kinetic information is very limited. Therefore the aim of this work was to propose a kinetic model for the degradation of mixed recalcitrant compounds from real wastewaters by copper based Fenton-type oxidation. In a first stage of our work, different active phases were explored using heterogeneous Cu (II), Fe (III), Ni (II) and Zn (II) phases supported on gamma alumina spheres (SASOL, 200 m2/g) and also commercial catalyst samples. The catalysts were characterized by XRD, SEM-EDX and N2 adsorption?desorption and tested for the catalytic wet peroxide oxidation (CWPO) of chemimechanical pulping wastewaters, at 70 ºC. The catalytic performance was monitored in terms of Total Organic Carbon (TOC), H2O2 consumption, pH variation, evolution of aromatic compounds and decoloration degree of effluent along the reaction. Preliminar findings showed only partial mineralization. Copper based systems exhibited the best TOC abatement performances, achieving carbon content reduction near 50% [3]. On the basis of these results, further kinetics studies were carried out using a home-made 2.5% CuO/γ-Al2O3 catalyst, in a temperature range of 45-80 ºC. Kinetic constants were found and activation energies of heterogeneous and homogeneous oxidations, and adsorption of organic matter on the catalyst were also determined. Three mechanisms were studied for TOC reduction in alkaline spent liquors: heterogeneous and homogeneous oxidations, and adsorption of organic matter on the heterogeneous catalyst. 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 followed by a slow one. The heterogeneous oxidation process was evaluated by examining temperature and catalyst load. Temperature affected dramatically the reaction and the kinetics constant increased linearly with the increase of catalyst load. TOC conversions and reaction rates of homogeneous oxidations were higher than those observed for the heterogeneous reactions. Adsorption of organic compounds onto CuO/γ-Al2O3 is mainly of physical nature. The simulated effluent from alkaline treatment of wood behaves as an anionic stream, with an easy adsorption to the active sites of alumina surface at lower pH.