Contamination of soils by automotive residual oil represents a global environmental problem. Bioremediation is the technology most suitable to remove this contaminant from the medium. Therefore, this work aimed to evaluate the effectiveness of bioremediation of automotive residual oil-contaminated soils by biostimulation with enzymes, surfactant, and vermicompost. The bioremediation efficiency was examined using a factorial design of 2⁴ to determine the effect of the time, pH and temperature conditions, biostimulation with enzyme-vermicompost, and biostimulation with enzyme-surfactant. Enzymes obtained from Ricinus communis L. seeds, commercial vermicompost, and Triton X-100 were used. Results showed that the highest removal efficiency (99.9%) was achieved at 49 days, with a pH of 4.5, temperature of 37 °C, and using biostimulation with enzyme-vermicompost (3% w/v–5% w/w). The addition of surfactant was not significant in increasing the removal efficiency. Therefore, the results provide adequate conditions to bioremediate automotive residual oil-contaminated soils by biostimulation using enzymes supported with vermicompost.

The present study investigated the effectiveness of two biopolymer coagulants on turbidity and chemical oxygen demand removal in urban wastewater. The biopolymers were produced from vegetal biomass using the mucilage extracted from Opuntia robusta cladodes, and Uncaria tomentosa leaves. Opuntia robusta is an abundant species in Mexico, which is not edible. Uncaria tomentosa is an exotic invasive species in Mexico and other countries, which negatively affects the ecosystems where it is introduced. A combined experimental design of mixture–process was selected to evaluate the effectiveness of both biopolymer coagulants regarding aluminum sulfate (conventional chemical coagulant). Results showed turbidity and chemical oxygen demand removal efficiencies of 42.3% and 69.6% for Opuntia robusta and 17.2% and 39.4% for Uncaria tomentosa biopolymer coagulant, respectively, at a dose of 200 mg/L. Furthermore, optimum conditions from the experimental design to reach the maximum turbidity and chemical oxygen demand removal were obtained at an Opuntia robusta biopolymer coagulant concentration of 10 mg/L, showing removal efficiencies of 68.7 ± 1.7% and 86.1 ± 1.4%, respectively. These results support using Opuntia robusta as an alternative biopolymer coagulant in urban wastewater treatment.

This study evaluated the potential of a biocoagulant produced from prickly pear peel waste valorization and its use as a biocoagulant aid mixed with aluminum sulfate to remove turbidity in domestic wastewater. A central composite design (CCD) and a simplex lattice design (SLD) of two components (biocoagulant and aluminum sulfate) were developed to determine the optimal doses and pH of the biocoagulant and optimal mixing proportions. Both designs optimized the coagulation process from an analysis of variance to fit the experimental data to mathematical models and an optimization analysis to obtain the highest percentage of turbidity removal. The results showed that a water pH of 4 and a biocoagulant dose of 100 mg/L are optimal conditions for a turbidity removal of 76.1%. The potential decreases to 51.7% when the wastewater pH is maintained at 7.8 and a dose of 250 mg/L is used. This efficiency could be increased to 58.2% by using a mixture with optimal proportions of 30% biocoagulant and 70% aluminum sulfate. The experimental data were fitted to two quadratic models, estimating model prediction errors of 0.42% and 2.34%, respectively. Therefore, these results support the valorization of prickly pear peel waste to produce a biocoagulant, which could be used in acid and alkaline wastewater or as a biocoagulant aid mixed with aluminum sulfate.

This study analyzed the lead concentrations in fruit grown near tailings dams of a mine in Zacatecas (Mexico) using electrochemical techniques. A 3 × 4 factorial design, with three levels of apple tree distance (low, medium, and high) and four levels of apple tree part (stem, leaf, pulp, and peel), was performed to predict the pathway for contamination (foliar or radicular). Samples of each apple tree part, soil, and irrigation water were collected. The lead concentrations were determined by anodic stripping voltammetry. The results showed lead concentrations of 172 ppm and 0.012 ppm for the soil and irrigation water, which were discarded as sources of contamination since they were below the allowable limits by the Mexican standards (400 ppm and 2 ppm, respectively). However, lead concentrations in the stem and leaf ranged from 6.6 ppm to 30.7 ppm, and pulp and peel exceeded 300 times the allowable limit by the Codex Alimentarius (0.1 ppm). The apple tree part was a significant factor in the experimental design. Hence, it was predicted that the pathway for contamination is by foliar absorption. The fruit is highly contaminated by its proximity to the mine. Therefore, mitigation actions must be performed to avoid health risks for the consumers of this fruit.