Nickel, although essential to plants, may be toxic to plants and animals. It is mainly assimilated by food ingestion. However, information about the average levels of elements (including Ni) in edible vegetables from different regions is still scarce in Brazil. The objectives of this study were to: (a) evaluate and optimize a method for preparation of vegetable tissue samples for Ni determination; (b) optimize the analytical procedures for determination by Flame Atomic Absorption Spectrometry (FAAS) and by Electrothermal Atomic Absorption (ETAAS) in vegetable samples and (c) determine the Ni concentration in vegetables consumed in the cities of Lorena and Taubaté in the Vale do Paraíba, State of São Paulo, Brazil. By means of the analytical technique for determination by ETAAS or FAAS, the results were validated by the test of analyte addition and recovery. The most viable method tested for quantification of this element was HClO4-HNO3 wet digestion. All samples but carrot tissue collected in Lorena contained Ni levels above the permitted by the Brazilian Ministry of Health. The most disturbing results, requiring more detailed studies, were the Ni concentrations measured in carrot samples from Taubaté, where levels were five times higher than permitted by Brazilian regulations.

In this study, a stochastic model was applied to investigate the degradation of landfill leachate by solar photo-Fenton processes. The coefficient of determination (R²) between experimental and predicted data ranged from 0.9958–0.9995. The optimal conditions for the initial phase (lasting 5–22 min) were high Fe²⁺ level, low pH level, and intermediate H₂O₂ level. For the second phase, optimal leachate degradation percentages were obtained by maintaining the pH, increasing H₂O_2, and decreasing Fe²⁺ to the lowest level. Determination of optimal reaction conditions (such as pH, Fe²⁺, and H₂O₂ values) for both degradation phases is of paramount importance for process scale-up. The major contribution of this study was the development of a tool that considers the effects of one or more reactions on organic carbon degradation. This was achieved by assessing the significance of the effects of experimental conditions on model parameters for the fast and slow steps of leachate degradation by advanced oxidation processes. GRAPHICAL ABSTRACT

Natural effluents with marked variation in their chemical composition over decomposition time in the matrix from which they are generated have a complex composition and are not totally known in most cases. Landfill leachate can be considered an effluent with complex composition, requiring imminent and more comprehensive studies on organic load degradation. Such complexity of numerous organic compounds (most of them recalcitrant humic and fulvic substances) demands a large number of kinetic equations to satisfactorily describe the temporal evolution of such conversion. Thereby, this work aims to study a kinetic approach grounded on previously consolidated chemical reactions of radical generation through the photo-Fenton mechanism. A molar balance was developed for each species in a batch photo-Fenton process and the resulting ordinary differential equations were numerically solved in MATLAB^TM. The kinetic model satisfactorily described an organic load conversion of the effluent under the various experimental conditions studied herein. Experimental trends could be represented by a free-radical mechanism and a degradation rate equation of first order for organic carbon, hydroxyl radical and H⁺. The model fittings revealed a hydroxyl radical/organic carbon stoichiometric ratio of 2:1. The kinetic study has confirmed the importance of pH levels for the reaction medium, and indicated that degradation rate depends on the medium organic composition, which provided an exponential function of conversion for the degradation rate coefficient. The model simulations corroborated the positive effect of sunlight on the radical generation through decomposition reaction with a rate coefficient in the range 4 × 10⁻³–2 × 10⁻¹ s⁻¹.

The agro-industrial systems comprise activities which transform raw materials of agricultural, aquacultural, livestock and forestry industries from primary production stages to consumption. Pig farming stands out in national and international markets for agro-industrial processes such as slaughtering and meat processing. Although this sector positively contributes to the economies of several countries, the high flow of waste resulting from implementing integrated production systems has led to serious environmental consequences (e.g., polluted water bodies and Greenhouse Gases - GHGs emissions). Among the treatment methods, anaerobic digestion reduces the organic load of biomass in the absence of oxygen, generating biogas and organic fertilizer. However, there are limitations associated with high CH4 variability and low yield, resulting a minimal and slow implementation in Brazil. Some research has reported the use of mineral additives to optimize the digestion process. This study comprises a bibliographic review of pig farming systems and production models, followed by an analysis on a global scale and environmental consequences. It is also discussed the use of additive minerals which have been applied in anaerobic digestion of swine manure as well as some prospects for global advances with opportunities to mitigate GHGs and bottlenecks. Despite being a promising technology, detailed evaluations of the use of these additives and their implementation in treatment plants must still be carried out in such a way to understand the optimization of such process.