The environmental impact of first-generation biodiesel production, particularly deforestation and soil degradation caused by palm and soybean cultivation, has raised concerns about sustainability. In contrast, second-generation biodiesel utilizes waste as feedstock, offering a more sustainable alternative. Used cooking oil (UCO), a significant waste stream, represents a viable feedstock for biodiesel production, reducing pollution and mitigating economic, environmental, and social challenges. While Europe has demonstrated successful UCO waste management strategies, many regions lack efficient systems, leading to improper disposal that causes water eutrophication, soil degradation, and increased wastewater treatment costs. This study develops a comprehensive strategy for UCO management to optimize its energy potential in biodiesel production, using Barranquilla, Colombia, as a case study. Transesterification, identified as the most efficient conversion method, achieves conversion rates of up to 90%. A pilot project in the Barranquilla area estimates that 963,070.95 kg of UCO is generated annually, with the potential to produce 902,108.56 kg of biodiesel. These findings contribute to the advancement of circular economy principles, offering an adaptable framework for sustainable biofuel production in other regions.

Dependence on fertilizers limits the sustainability of tropical agriculture. Remineralization using rock byproducts offers a solution that is conditioned by the mineralogical–soil interaction. This study evaluated the agronomic and geochemical potential of a gabbro rock byproduct (GRB) as a bulk amendment in yellow maize (Zea mays L.) cultivation in Atlántico, Colombia. The specific objectives were (1) to characterize the mineralogy and geochemistry of the local GRB; (2) to quantify its neutralizing and fertilizing effect in an acidic Arenosol soil; and (3) to evaluate the biometric response of yellow maize (Zea mays L.) in a field trial. The trial was conducted in an acidic haplic Arenosol (pH 5.4) in 2023, with a 70-day cycle, comparing three management systems: M1 (control), M2 (47 Mg·ha⁻¹ GRB, seed type: ICA-109), and M3 (47 Mg·ha⁻¹ GRB, seed type: V-114). The assessed GRB, with 52.75% SiO₂ and 5.46% CaO, is rich in calcic plagioclase, clinopyroxenes, and zeolites. Application of GRB at 47 Mg·ha⁻¹ in treatment M3 coincided with marked changes in soil properties over the course of the trial, with pH rising from 5.4 to 6.4, cation exchange capacity from 5.0 to 12.1 cmol_c·kg⁻¹, and available phosphorus from 9.8 to 35.0 mg·kg⁻¹. Plants in M3 showed statistically significant increases (p < 0.001) in ear weight (median: 150 g vs. 60.5 g in M1) and in vegetative development. Because the trial was pseudo-replicated, used a high single-dose “shock-loading” rate, involved different maize genotypes across treatments, and covered only one 70-day cycle, these results should be interpreted as exploratory and site-specific. Even so, they indicate that GRB can act as an effective acidity corrector and slow-release multinutrient source under Arenosol conditions, with relevance for circular-economy strategies. Future work should evaluate agronomically doses, include replicated multi-cycle trials, and incorporate comparative and risk-assessment analyses.

The progressive deterioration of surface water quality due to natural and anthropogenic factors, together with the limitations associated with conventional chemical coagulants, has driven the development of natural coagulants as sustainable alternatives for water treatment. In this context, the present study analyzed the production and application of a chitosan-based natural coagulant obtained from Oreochromis niloticus fish scales through a chemical method. The first phase involved biopolymer extraction through depigmentation, deproteinization, demineralization, and deacetylation; the second phase evaluated its performance as a coagulant using jar tests with water from the Magdalena River; and the third phase consisted of statistical analysis of the results using ANOVA. Yields of 78%, 78.20%, 88.52%, and 30% were obtained for each processing stage, and the chitosan achieved a degree of deacetylation of 76.87%, confirming its potential for water treatment applications. Optimal conditions were determined as a coagulant dosage of 300 mg/L and a flocculation time of 30 min, while ANOVA results indicated that both variables significantly influenced turbidity removal (p < 0.05). Under these conditions, a turbidity reduction of 76.30% was achieved. However, the final turbidity and color values did not meet Colombian regulatory standards, which was attributed to the presence of residual minerals and a moderate degree of deacetylation. Overall, the results demonstrate that chitosan derived from fish scales represents a sustainable alternative to chemical coagulants; however, process optimization and complementary treatment stages are required to meet drinking water standards.