The increasing generation of agricultural waste poses both environmental and economic challenges, particularly in rural areas with limited infrastructure. Anaerobic digestion has emerged as a sustainable alternative, enabling the valorization of waste and the production of biogas and biofertilizer. This study evaluated the economic and environmental gains of mono- and co-digestion of equine manure and vegetable waste using biodigesters of different capacities across four simulated projects—Project 1 (15 m² biodigester with monodigestion), Project 2 (15 m² biodigester with co-digestion), Project 3 (20 m² biodigester with monodigestion), and Project 4 (20 m² biodigester with co-digestion). Economic feasibility was assessed through indicators such as Net Present Value (NPV), Internal Rate of Return (IRR), Modified IRR (MIRR), Profitability Index (PI), Benefit-Cost Ratio (B/C), Discounted Payback Period, sensitivity analysis, and Monte Carlo simulation, adopting a Minimum Attractiveness Rate (MAR) of 6.43% per year. Environmental benefits were estimated based on the annual reduction of CO₂ equivalent emissions. The results showed that all projects were economically viable and had the potential to mitigate up to 36 tons of CO₂eq per year. Additionally, an eco-efficiency indicator (NPV per CO₂eq avoided) was calculated to enable an integrated assessment of economic performance and environmental impact. Projects using 20 m³ biodigesters achieved the best results, with Project 3 being the most eco-efficient (USD256.05/tCO₂eq), while Project 4 yielded the highest absolute return in all economic analysis tools: NPV (USD 9063.81), IRR (25.10%), MIRR (10.95%), PI (USD 1.65), B/C (USD 1.65) and DPP (4.56 years). The integrated analysis underscores the significance of co-digestion and economies of scale in encouraging the adoption of this technology by small rural producers.

Fish-processing residues represent a significant environmental challenge due to their high moisture and nitrogen contents, which favor greenhouse gas (GHG) emissions during degradation. This study evaluated how different waste management strategies affect GHG emissions from fish waste, including conventional composting (Bulk), composting amended with biochar (BulkBioch), burial with soil (S), and burial with soil plus sawdust (BulkS). Daily emissions of CH₄, N₂O, and CO₂ were monitored, and cumulative emissions were modeled using generalized additive models. Composting treatments (Bulk and BulkBioch) released higher CO₂, suggesting greater microbial degradation, while burial treatments developed earlier anaerobic conditions with reduced decomposition efficiency. Bulk showed the highest cumulative CH₄ and CO₂ emissions, whereas N₂O fluxes were greater in burial methods, reaching 2.18 g N₂O kg⁻¹ TS in S. Biochar addition was associated with 15% and 10% lower CH₄ and N₂O emissions, respectively, and earlier stabilization of CH4 emissions. In global warming potential, BulkBioch presented the lowest climate impact (305 g CO₂-eq kg⁻¹ fish), followed by Bulk (338 g CO₂-eq kg⁻¹), whereas BulkS reached up to 599 g CO₂-eq kg⁻¹. The use of bulking agents in burial resulted in lower CH₄ buildup and greater nutrient retention. Overall, combining bulking agents and biochar may represent a promising strategy to mitigate GHG emissions while supporting nutrient conservation.

Monensin supplementation in ruminant diets to improve energy efficiency also results in the excretion of this compound through manure. However, in sheep, monensin excretion rates remain unknown and are of concern due to the potential risks of environmental contamination, as well as possible impacts on waste treatment and recycling processes. Therefore, the objective of this study was to evaluate monensin excretion in sheep manure and its influence on the anaerobic digestion of these residues when increasing dietary doses of monensin were administered. Sheep were fed 0, 8, 14, and 20 mg of monensin kg⁻¹ of dry matter intake, and the collected manure was used to prepare substrates for feeding biodigesters. The substrates were digested either as whole material or after sieving for separation and removal of the solid fraction and were maintained under anaerobic digestion for hydraulic retention times (HRT) of 20 and 30 days. Increasing monensin doses resulted in higher excretion rates, reaching 13.32%, 32.01%, and 34.57% for the 8, 14, and 20 mg doses, respectively. When fraction separation was performed prior to digestion, higher monensin concentrations were detected in the sieved substrates; however, the loading rates applied to the biodigesters were similar. During anaerobic digestion, fraction separation promoted greater reductions in volatile solids, with mean reductions of 47.88% and 53.30% for HRTs of 20 and 30 days, respectively. Consequently, biogas production potential increased, reaching 220.6 and 306.4 L kg⁻¹ VS, with methane concentrations of 72% and 69.87% for HRTs of 20 and 30 days, respectively. Both HRTs were effective in reducing monensin levels, achieving a minimum removal efficiency of 80.14% by the end of the digestion process. Under the conditions of this study, a 30-day HRT combined with prior solid–liquid separation improved biogas and methane production. However, further studies are needed to evaluate economic feasibility, scalability, operational costs, and management of the separated solid fraction.

This study evaluated the effects of application rates of two biocomposts derived from fishery waste, produced with and without biochar, on lettuce growth and assessed the economic feasibility of small-scale lettuce production using these materials. A completely randomized 2 × 4 factorial design was used, comprising two biocompost types (with and without biochar) and four application rates (0, 25, 50, and 100 g per 2 kg of soil), with four replicates per treatment. Lettuce growth was evaluated over 30 days based on plant weight and length, aboveground biomass and length, root weight and length, and dry matter content. Application rate significantly affected total plant weight and length, aboveground biomass and length, and root length (p < 0.05). The 100 g rate resulted in the highest mean total plant weight (208.85 g) and aboveground biomass (167.31 g), representing increases of 207.8% and 248.3%, respectively, compared with the untreated control. Mean aboveground length was also greatest at this rate (20.13 cm), whereas root length was greatest at 25 g (25.73 cm). Biocompost type significantly affected root weight and dry matter content, with higher mean values in the treatment without biochar (24.61 g and 88.33%, respectively) than in the treatment with biochar (18.71 g and 86.73%, respectively). The economic analysis, based on lettuce production in a 96 m² greenhouse, indicated that the project was economically feasible, with an Equivalent Annual Uniform Value (EAUV) of US$545.67, a Profitability Index of 1.86, and a Benefit–Cost Ratio of 1.50. Sensitivity analysis showed that the selling price of lettuce was the main determinant of project profitability, accounting for 99.5% of the modeled variation in Net Present Value. These findings indicate that fishery waste-derived biocomposts have potential for lettuce production, while economic success depends strongly on maintaining favorable market prices.