Search

Agro-industrial waste is generated in large quantities, producing negative environmental impacts. For instance, in the distillation process of vinasses, up to 15 L are produced per alcohol produced. Therefore, it is necessary to search for ecological alternatives. Biological treatments are not recommended because vinasses contain compounds, such as melanoidins, which exert inhibitory activity against microorganisms. Thanks to this activity, melanoidins could be removed, recovered, and become a value-added product. In this study, Opuntia ficus-indica (OFI) mucilage, a natural biopolymer as coadjuvant, was used to improve the coagulation-flocculation process in the treatment of real samples of mezcal vinasses, after evaluating the individual effect of aluminum sulfate and ferric chloride. It was possible to eliminate 90% of color using ferric chloride, showing better removals than aluminum sulfate. However, the effect of ferric chloride plus OFI mucilage generated an adverse effect because the removal was under 17%. The individual effect of ferric chloride for chemical oxygen demand (COD) removal was 28%. This removal was improved by the addition of OFI mucilage, as it was able to increase removal to 84%. The natural coadjuvant was shown to be effective in the COD removal in the treatment of mezcal vinasse using the coagulation-flocculation process.

Bismuth is one of the most difficult impurities to remove in mining concentrates and low concentrations generate problems in silver and copper refineries. Therefore, financial penalties are established when concentrations exceed 0.05%. Some researchers had used arsenic to remove bismuth with results of up to 52% of extraction. Unfortunately, this mechanism is not yet fully understood. The objective of this research was to obtain the solubility parameters of amorphous mineral compounds, including bismuth-based compounds, through computational simulation using molecular dynamics. The composition of the mineral sample was determined by X-ray diffraction and the crystalline species were obtained and modeled using Materials Studio software. The nanostructures were optimized by an energy minimization methodology using the Broyden-Fletcher-Goldfarb-Shanno algorithm and were validated using the figure of merit equation and density. Simulations were performed using the Universal Force Field at constant pressure and temperature. The results of the minerals identified in the sample were compared with arsenic trioxide, indicating miscibility between As2O3and Bi2O3, possible miscibility with 10 other minerals, and immiscibility with the rest. The results indicate that As2O3 can be successfully used for the removal of Bi2O3 without a negative effect on the recovery of other minerals of higher commercial value.

Many organic residues are being wasted since they are not given a comprehensive management; anaerobic digestion is an alternative to reduce the impact of these residues, and to produce biogas. The chapter includes the state of art about biogas and energy production, and later, the analysis of a study case focusing on the use of pulp and paper wastes to produce biogas. The study was carried out through anaerobic digestion at a bench scale using three temperature phases to treat primary and secondary sludge, establishing operational parameters such as temperature, retention time, and organic loadings. Monitoring of volume, methane concentration in the biogas, volatile solids reduction, volatile fatty acids during the process, the performance of the process in function of methane produced per volatile solids removed is calculated. This case study shows that it is feasible to use the sludge from the company’s wastewater treatment plant (WWTP) for the generation of biogas, thus reducing waste management problems.

This study focused on determining the optimal conditions for lead removal in aqueous solution models, by the spherical agglomeration technique (SAT), modifying the dose of Agave lechuguilla Torr. (lechuguilla) extract, used as biosurfactant. The SAT operating conditions at room temperature were: Initial pH 9, and constant agitation ω = 600 rpm. Experiments were performed under a 5x3 factorial design with five lechuguilla extract doses (0.3 - 2.0 g extract/g of pollutant), three different lead concentrations (1, 5 and 10 mg/L) and, for the SAT last stage, two different dosage ratio of CaCl2 (10:1 and 20:1 parts of Ca2+ by part of pollutant). Residual lead, sodium and calcium were determined by atomic absorption spectroscopy. According to statistical analysis, significant effects were observed for calcium dosages, initial lead concentration, extract dose and their interaction. The lead removal efficiency obtained by SAT reached 99.8%.

Effluent found in the pulp and paper industry can cause considerable damage if it is discharged untreated, because of the high biochemical and chemical oxygen demands. Electrocoagulation is a physicochemical process widely used in industrial wastewater treatment. The removal of different pollutants depends on the sample type and operating conditions. The aim of this research was to evaluate the efficiency of an electrocoagulation system for COD removal from recycled paper production effluent via aluminum and iron electrodes. Different operational parameters, such as the electrolysis time (5 min to 15 min), current density (7 A/m2 to 11 A/m2), and distance between each electrode (5 mm to 20 mm), were evaluated. The turbidity, total suspended solids, chlorides, sulfates, and COD had removal efficiencies of 92.7%, 91.3%, 70.4%, 66.6%, and 64%, respectively. A polynomial model was generated to estimate the optimum conditions for COD removal. The optimum times for the current densities 7 A/m2, 8 A/m2, 9 A/m2, 10 A/m2, and 11 A/m2 were 39.5 min, 39.5 min, 35.7 min, 34.1 min, and 32.8 min, respectively, with a 15-mm electrode gap.

The aim of this research was to evaluate bioleaching of Mn, As, Pb and Zn from mining tailings using two different sets of variable processing conditions. In the first set pH (2.0, 4.0 and 6.0), tailings concentrations (10, 20 y 30 %, w/v [111.11, 250.00 and 428.57 g/L, respectively]), and two types of culture medium (9K [with nitrogen source] and nonN (nitrogen-free medium) were evaluated; in the second set the evaluation focused on continuous supplementation of biogenic H 2 SO 4 oxidized with two types of culture medium (9K and nonN) at different tailings concentrations (10, 20 y 30 %, w/v [111.11, 250.00 and 428.57 g/L, respectively]), with continuous supplementation of the media previously described (9K and nonN) oxidized by the native strains Leptospirillum ferriphilum and Leptospirillum ferrooxidans . In the first set, the highest removal of Mn (93.49 %), As (13.92 %) and Pb (> 99 %) was observed in both media at 10 % of tailings and initial pH of 2.0. In the second experimental set, the highest removal of Mn (99 %), As (> 85 %), Pb (> 99 %) and Zn (67 %) was found with both media at 10 % of tailings and initial pH 6.0. Continuous supplementation of biologically acidified and oxidized culture media enhanced the metals removal from solid waste or tailings. Similar metals removal in media without nitrogen compared to medium with nitrogen was observed in this research.