José Carlos Escobar Palacio

Background: Dark fermentation (DF) of organic solid waste (OSW) is a promising route for sustainable biohydrogen (bioH₂) production, but it is often limited by slow interspecies electron transfer and by acidification of the medium. Promoting direct interspecies electron transfer (DIET) with conductive additives is a candidate strategy to intensify the process. Objective and methods: This study compares the effect of magnetite (Fe₃O₄), granular activated carbon (AC), and laboratory-synthesized nickel–iron-doped activated carbon (DC) on the DF of genuine post-consumer food waste. Batch assays were conducted in 2.1 L anaerobic reactors under mesophilic conditions (35 °C), in triplicate, using food waste as the substrate and raw UASB sewage sludge as a mixed inoculum, without pH control. Biohydrogen was quantified with a portable biogas analyzer and expressed as mL H₂/g COD removed; the additives were characterized by SEM–EDS, and yields were compared by one-way ANOVA with Tukey post hoc test (α = 0.05). Main findings: Additive type had a highly significant effect on biohydrogen yield (F(6,14) = 48.7; p < 0.001; η² = 0.954). DC at 4 g achieved the best performance, reaching 0.271 mL H₂/g COD removed (≈4.5-fold higher than the additive-free control) and COD removals of 65.8–72.4%, whereas magnetite produced only sporadic, non-reproducible gains and undoped AC gave a modest, consistent improvement. Excessive acidification (final pH 2.5–3.1), attributed to the accumulation of volatile fatty acids under the deliberately unbuffered conditions, was the main operational limitation and is interpreted as a conservative ceiling on the yields reported here. Prospects: Metal-doped carbonaceous materials emerged as the most robust and reproducible strategy for intensifying DF of food waste; future work should couple this route with pH buffering and with electrochemical and microbial-community analyses to confirm the DIET contribution and to support scale-up in integrated biorefineries.

This study evaluated the techno-economic feasibility of green hydrogen production using solar photovoltaic energy under conditions representative of the state of Minas Gerais, Brazil. A 10 MWp photovoltaic system integrated with three electrolysis technologies was considered: alkaline (AEL), proton exchange membrane (PEM), and solid oxide (SOE) electrolyzers. The economic analysis was conducted using a deterministic scenario and a probabilistic approach based on a Monte Carlo simulation with 10,000 scenarios, incorporating uncertainties related to electrolyzer CAPEX, solar irradiation levels, hydrogen selling price, and interest rates. The results of the deterministic scenario indicated that only the alkaline electrolyzer yielded a positive Net Present Value (NPV), whereas PEM and SOE technologies showed economically unfavorable results, primarily due to higher investment costs. Probabilistic analysis revealed high exposure to economic risk under current market conditions, with only 6.16% of simulations yielding a positive NPV in the most restrictive scenario. However, when scenarios involving moderate to significant reductions in electrolyzer CAPEX, combined with increasingly favorable market conditions for hydrogen sales, were considered, the probability of a positive NPV rose to 63.25% in the intermediate scenario and 97.65% in the optimistic scenario. The results indicate that the economic viability of green hydrogen production is highly sensitive to technology costs and the hydrogen selling price, underscoring the importance of technological advancements, economies of scale, and incentive policies for the expansion of this technology in Brazil.

Minas Gerais is Brazil’s largest charcoal producer, relying on carbonization kilns that release effluent gases and waste energy while generating environmental impacts. This work evaluates the electricity generation potential from these gases using different conversion technologies. A database-based assessment of charcoal production units, based on official institutional records, enabled estimating the energy potential for 2020 and projecting it to 2030. Three technologies were assessed: Steam Rankine Cycle, Organic Rankine Cycle, and Externally Fired Gas Turbine. For each one, efficiencies were calculated and applied to the surveyed producers, ranging from 5% to 24% for power capacities between 100 kW and 2000 kW. The highest energy generation potential, 1348 GWh/year, was obtained using the regenerative and superheated ORC with n-decane as the working fluid. In addition, an economic analysis was performed based on Brazilian electricity auction prices, together with a sensitivity analysis of key variables, including installed power, electricity price, minimum attractiveness rate, taxes, operating hours, and capital expenditure. The results demonstrate that current technical and economic conditions are unfavorable for implementing waste-heat-based power plants in Minas Gerais. Plants below 10 MW are especially unfeasible. A Life Cycle Assessment estimated emissions of 2437.7 kg CO₂eq per ton of charcoal. Sustainable measures such as eliminating native wood use, increasing Gravimetric Yield, and adding afterburners could reduce emissions by over 57%.

This study presents a methodology for assessing the technical and economic potential of electricity generation from biomass residues, using thermochemical conversion technologies. Applied in the state of Minas Gerais, Brazil, the analysis focuses on residues from corn, soybean, coffee, eucalyptus, and sugarcane. A multi-criteria decision-making (MCDM) approach, integrated with GIS, was used to identify the most viable biomass sources and most suitable conversion technologies, namely the Rankine cycle, organic Rankine cycle, and gasification with internal combustion engines, based on Technological Readiness Levels (TRLs). Eucalyptus emerged as the most suitable residue due to its high energy density, while sugarcane residues were the most abundant. The economic feasibility analysis indicates levelized costs ranging from USD 0.10 to USD 0.24 per kWh, with the conventional Rankine cycle emerging as the most cost-effective option for plants with a capacity exceeding 5 MWe. The proposed methodology supports strategic bioenergy planning by integrating geospatial, technological, and economic factors.

Over recent decades, human activities have essentially depended on fossil fuels. The last Intergovernmental Panel on Climate Change reports recommend a shift to renewables and a more energy-efficient economy. To fulfill the potential of bioenergy, tools are required to overcome the complexities of the decision-making processes for viable projects. This work presents a decision-making tool to select the most feasible biomass residues and a case study of the state of Minas Gerais, in Brazil. Among the 13 evaluated criteria, eucalyptus residues demonstrated the highest potential for electricity production, followed by sugarcane bagasse and coffee husks. The choice of Minas Gerais as a case study is important due to its diverse agricultural landscape and the potential for biomass residue generation. The presented methodology uses the Analytical Hierarchy Process (AHP), a multi-criteria decision-making method (MCDM). Thirteen criteria were required to enable the best choice of biomass residue alternatives for electricity generation, which experts in the bioenergy field evaluated. The technical criterion was shown to be the one with the highest degree of importance. The results of the study identified that CO_2eq emissions (11.46%) and electricity demand (ED) were the most relevant sub-criteria for prioritizing the viability of agricultural waste. Eucalyptus was ranked as the most promising biomass, followed by sugarcane bagasse and coffee husks. In addition, the use of GIS tools made it possible to map the regions with the greatest potential in Minas Gerais, providing a robust approach to identifying strategic sites for bioenergy.

The contribution of this chapter is to deepen and widen existing knowledge on municipal solid waste (MSW) management by analyzing different energy recovery routes for MSW. The main aspects related to the composition of waste are addressed, as well as the technological routes for thermochemical and biochemical energy usage. Within the thermochemical route, incineration is currently the most utilized technology for energy recovery of waste, with generation of electricity and heat and also a decrease in the volume of the produced waste. Gasification and pyrolysis are alternatives for the production of chemical products from wastes. The biological route is an interesting alternative for the utilization of the organic fraction of MSW, as aerobic or anaerobic processes enable the production of biogas and of a compound that can be utilized as a fertilizer. Depending on the size of the population, composition of waste, and products to be obtained (energy or chemical), more than one technology can be combined for a better energy usage of waste.

The goal of this work is to understand the gasification process for Miscanthus briquettes in a double-stage downdraft gasifier, and the impact of different Equivalence Ratios (ER) on syngas, biochar, and tar characteristics. The optimal ER was found to be 0.35, which yielded a syngas maximum heating value of 5.5 MJ/Nm³ with a syngas composition of 20.29% CO, 18.68% H₂, and 0.86% CH₄. To better understand the observed behavior, an equilibrium reaction model was created and validated using the experimental data. The model showed that the heating value decreased with increasing ER, and that hydrogen production peaked at ER = 0.37, while methane (CH₄) became negligible above ER = 0.42. Tar and particle content in the gas produced at a certain temperature can now be predicted. To assess the biochar characteristics, surface structure image analysis and a surface area porosity analysis were carried out. Employing images from a scanning electron microscope (SEM), the biochar cell bonds and pore structures were examined and analyzed. By using the Brunauer-Emmett-Teller (BET) analysis of the surface porosity, the surface area to be 186.06 m²/g and the micro pore volume was calculated to be 0.07 m³/g. The final aspect of the analysis involved an evaluation of tar production. Combining current and prior data showed a logarithmic relationship between the amount of tar produced and the gasifier bed temperature, where the amount of tar produced decreased with increasing bed temperature. This results in very low tar levels, which is one of the known advantages for a double-stage downdraft gasifier over a single-stage system.

The growing demand for energy, is caused by the exponential increase of the world population. The use of solar energy through photovoltaic and CSP technologies is also growing. In this last one, it is necessary to use systems to ensure tracking and positioning perpendicular of the sun, for medium and high temperatures. This is commonly done by modeling, getting the angles that x the sun perpendicular to the capture system. Studies show that the use of solar tracking increases the energy delivery efficiency between 15% and 40%. Several techniques can be used for solar tracking, one of which is based on the use of controllers that use fuzzy logic. These control strategies allow us to analyse complex processes and make decisions to ensure a more precise answer. Thus, this paper presents the configuration of a fuzzy logic based controller, developed in Labview tool Release 11.00. To ensure the position perpendicular to the sun. The controller was created by correcting the output function, being compared with the error, reducing the "overshoot maximum (Mp)" and the "setting time (Ts)" and thus obtaining the wake of "MPPT" of the energy generated by solar systems. A methodology known as analysis of the critical points, was used. A demanda mundial de energia é crescente, causada principalmente pelo aumento exponencial da população do planeta. O uso de energia solar por meio das tecnologias fotovoltaica e heliotérmica também cresce. Para médias e altas temperaturas, no caso da tecnologia heliotérmica, é indispensável o uso de sistemas de controle que garantam o rastreamento e posicionamento perpendicular ao sol. Isto é comumente realizado mediante modelagem, obtendo os ângulos que relacionam a perpendicularidade do sol com o sistema de captação. Estudos comprovam que o uso do rastreamento solar aumenta a eficiência de entrega de energia entre 15% e 40%. Diversas técnicas podem ser empregadas para o rastreamento solar, sendo que uma delas está baseada na utilização de controladores que usam a lógica difusa. Estas estratégias de controle permitem analisar processos complexos e tomar decisões que garantam uma resposta mais precisa. Assim, apresenta-se neste trabalho a configuração de um controlador baseado em lógica difusa, desenvolvido na ferramenta Labview versão 11.00. Para garantir o posicionamento perpendicular ao sol, o controlador foi criado corrigindo a função de saída, sendo comparada com o erro, reduzindo o “maximum overshoot (Mp)” e o “setting time (Ts)” e assim obtendo o seguimento do “MPPT” da energia gerada pelos sistemas solares. Empregou-se ainda a metodologia conhecida como análise dos pontos críticos.