Catalytic wet peroxide oxidation: a route towards the application of hybrid magnetic carbon nanocomposites for the degradation of organic pollutants. A review

Several motivations have prompted the scientific community towards the application of hybrid magnetic carbon nanocomposites in catalytic wet peroxide oxidation (CWPO) processes. The most relevant literature on this topic is reviewed, with a special focus on the synergies that can arise from the combination of highly active and magnetically separable iron species with the easily tuned properties of carbon-based materials. These are mainly ascribed to increased adsorptive interactions, to good structural stability and low leaching levels of the metal species, and to increased regeneration and dispersion of the active sites, which are promoted by the presence of the carbon-based materials in the composites. The most significant features of carbon materials that may be further explored in the design of improved hybrid magnetic catalysts are also addressed, taking into consideration the experimental knowledge gathered by the authors in their studies and development of carbon-based catalysts for CWPO. The presence of stable metal impurities, basic active sites and sulphur-containing functionalities, as well as high specific surface area, adequate porous texture, adsorptive interactions and structural defects, are shown to increase the activity of carbon materials when applied in CWPO, while the presence of acidic oxygen-containing functionalities has the opposite effect.

Amphiphilic catalysts for the treatment of oily wastewaters

The main objective of this study was to obtain an effective catalyst for removal of diazo dye - Sudan IV by Catalytic Wet Peroxide Oxidation (CWPO). For this purpose liquid phase treatment was used to increase the basicity of activated carbon surface favoring the adsorption of organic pollutants. Modified activated carbon catalysts were used in different types of experiments: 1) decomposition of H2O2 in aquatic media, 2) decomposition of H2O2 in organic media, 3) adsorption of Sudan IV, 4) Sudan IV removal by CWPO. As the result of all of these experiments the most effective catalyst was obtained and discussed. It was not observed removal of Sudan IV from biphasic system by CWPO. The obtained results in some cases show a slight increase in concentration of Sudan IV, which may be ascribed to experimental errors. Different factors could be the reason of those errors. For example, the high volatility properties of organic media used in experiments should be taken into account during experiments. Under settled reaction temperature the decrease of cyclohexane volume during experiment could give rise in Sudan IV concentration. The initial concentration of model diazo dye also should be reviewed more detailed for CWPO experiments. Despite of these experimental errors the behavior of our catalysts in different media was observed.

Mineral and organic pollution in river Sabor (Northeastern Portugal): ecotoxicological effects on freshwater fauna

Aquatic ecosystems are final collectors of all kinds of pollution as an outcome of anthropogenic inputs, such us untreated industrial and municipal sewage and agricultural pollutants. There are several aquatic ecosystems that are threatened by mineral and organic pollution. In Northeastern Portugal, near Bragança, different watercourses are suffering negative impacts of human activities. It has been developed several studies in the monitoring of environmental impacts in these river basins, namely in Rio Fervença, affected by organic pollution, and in Portelo stream, affected, since 2009, by the collapse and continuous input of mining deposits. In this sense, the present study aimed to continue the monitoring study of ecological status of freshwater ecosystems of Northeastern Portugal, namely the following objectives: a) mineral pollution effects of mining deposits sudden incorporated into Portelo stream; b) organic pollution due to domestic and industrial inputs in River Fervença. Also, since fish are useful experimental models to evaluate toxicological mechanisms of contaminants, c) acute toxicity tests with Cu were conducted in laboratory conditions. During 2015/2016, it was made abiotic and biotic characterization of 16 sampling sites distributed by both Portelo and Fervença rivers, tributaries of main River Sabor (Douro Basin). Several physicochemical parameters were determined and Riparian Quality (QBR Index) and Channel Quality (GQC) Indexes were determined for habitat evaluation. Fish and invertebrate communities were sampled, according to protocols of Water Framework Directive (WFD). Several metrics were determined, with particular emphasis on the Biotic Index IBMWP and the Northern Portuguese Invertebrate Index (IPtIN). Acute toxicity tests were conducted with an Iberian fish species, common barbel (Luciobarbus bocagei) and some plasmatic electrolytes levels were evaluated, to assess their contribution to mitigate osmoregulatory adverse effects of Cu. Also, same electrolytes were measured after changing to clean water, in attempt to assess fish capacity to reverse this situation. Results obtained for both rivers showed a significant level of disturbance that affected decisively water, habitat and biological quality of aquatic ecosystems. Mineral and Organic Pollution in River Sabor (NE Portugal): Ecotoxicological Effects on Freshwater Fauna Due to this change of environmental conditions in Portelo stream (extreme pH values, high conductivity and presence of heavy metals), several biological metrics (e.g. taxonomic richness, abundance, diversity, evenness) confirmed, comparatively with reference sites, a substantial decrease on ecological integrity status. The same pattern was found for Fervença River; however other water parameters, namely the content of most limiting nutrients (e.g. N and P) seemed to have more influence in the composition and structure of macroinvertebrate and fish communities. In fact, despite the operation of the Sewage Treatment Plant of Bragança, Fervença River presented significant levels of disturbance that affected decisively the quality and ecological integrity of the aquatic ecosystem. The synergic effect of domestic and industrial pollution, intensive agriculture, regulation and degradation of aquatic and riparian habitats contributed to the decrease of ecological condition, namely in the downstream zones (after Bragança). The results for acute toxicity, showed that fish can change Na+ and K+ levels face to Cu exposition and, depending of Cu concentration tested, can also return to normal levels, providing some insights to that are believed to occurred in fish population, near the Portelo mines. The low ecological integrity status detected in the lotic ecosystems in NE Portugal as a result of mineral and organic pollution deserves the development of several measures for rehabilitation and improving of water quality. On the other hand, environmental education actions are needed to contribute to improvement of ecological integrity of the river and its conservation.