Pig farms have been identified as one of the most important sources of greenhouse gas emissions. This study demonstrates the production of vehicle biomethane in a demonstration prototype plant based on photosynthetic upgrading technology, where the CO₂ and H₂S present in biogas are consumed by a microalgae culture. The information collected during the prototype construction allowed for an assessment of the capital and operating costs of this novel biogas upgrading technology with other conventional systems. With this objective, the costs of the equipment comprising the biogas cleaning and purification system were calculated considering a biogas flow rate of 5 m³ h⁻¹, corresponding to a small–medium biogas plant and an average pig farm size. The sustainability and competitiveness of the algae upgrading system and the low capital and operating costs vis à vis other upgrading technologies were proven. With a net energy production of 687 kWh day⁻¹ and an annual profit of €30,348 in a 3500 head pig farm, this technology can be easily installed in livestock farms, increasing the benefits and reducing the carbon footprint.

Cereal straw stands out as one of the most abundant and globally distributed agricultural residues. Traditional applications cope with a limited amount of production, leaving the remainder in the field for natural decomposition. Managing cereal straw through controlled biological transformation under anaerobic conditions holds the potential to generate added value in the form of bioenergy. However, the lignocellulosic composition of these substrates poses challenges for organic degradation, often requiring energy-intensive pretreatments. A detailed study with a comprehensive calculation of the overall energy balance of the integrated process is proposed, aiming to provide real added value and replicability. Three scenarios for wheat straw transformation were investigated, incorporating two preliminary pre-treatment stages—mechanical milling and physicochemical steam explosion. Three conditions of pretreatment were essayed, varying the time exposure of the steam explosion. The subsequent energy integration analysis revealed that the process was optimized by up to 15% in the final energy balance when the steam explosion was set to 10 min. The macromolecular composition determination revealed that the thermal pretreatment reduced the lag phase of the hydrolysis step through hemicellulose breakdown.

Wine lee generation, a by-product of the wine industry, implies economic challenges for producers in terms of management due to its high organic load and low pH value. Biological treatment based on controlled anaerobic digestion may emerge as a viable management alternative given its promising potential for biogas production thanks to the organic content of the substrate. However, the complex properties of wine lees may lead to microbial activity inhibition and process kinetics failure. Various solutions have already been explored, including co-digestion with other substrates, or the application of different pretreatments, to mitigate the effects of the accumulation of phenolic compounds, volatile fatty acids, antioxidants, or the acidic pH value of the medium. In this study, laboratory-scale batch reactors were established, adding iron- (magnetite) or carbon (graphite)-based microparticles to assess their impact on the kinetics of the process. The results demonstrate a significant improvement of 35% in the potential production of biomethane after four days of operation with graphite particles and 42% after five days using magnetite particles. Methane production rates, as determined by the Gompertz model, were 45.38 and 46.54 mL CH₄∙gVS⁻¹∙d⁻¹ for the application of graphite and magnetite microparticles to the medium, respectively, compared to the value of 33.46 mL CH₄∙gVS⁻¹∙d⁻¹ for the control trial, confirming kinetic process improvements of 36% and 39%, respectively. Evidences of the acceleration of the methanogenesis phase were detected along the essays; however, the strong inhibition mediated by the carboxylate accumulation was not avoided in any of the tested conditions.

The ongoing global population growth and the corresponding rise in energy demand have contributed to increased greenhouse gas (GHG) emissions. The integration of alternative, locally sourced energy solutions such as biogas presents a promising strategy to partially offset conventional energy consumption. In this context, countries like Colombia—characterized by a high availability of organic waste such as palm oil mill effluent (POME), rice straw, and pig manure—have the potential to harness these residues for biogas production. This study integrates experimental assays of anaerobic co-digestion tests with the spatial analysis of substrate distribution through GIS tools, enabling the identification of optimal regions for biogas production. Methane yields reached 412 mL CH₄/g VS, comparable or superior to those reported in similar studies. In addition to laboratory assays, Geographic Information System (GIS) tools were used to generate a weighted heatmap index based on feedstock availability (POME, rice straw, pig manure) across 40 municipalities in Colombia. This integrated approach supports decentralized renewable energy planning and helps identify optimal locations for biogas plant development.

Anaerobic digestion of animal manure generates biogas and removes biodegradable organic matter, while most of the nitrogen and phosphorous remains at very high levels after the process. A subsequent microalgae culture in the digestate provides nutrient uptake at very low operational and installation costs. However, the dark color of manure digestate prevents light penetration, reducing the rates of algae growth. Ozonation was researched as a strategy for color removal followed by microalgae culture. Although similar biomass production was achieved in treated and untreated digestates (1.09 vs. 0.99 g L⁻¹), the positive effect of ozonation was evidenced by the significantly higher rates of photosynthetically produced oxygen: 0.804 and 0.18 mg O₂ mg⁻¹ TSS min⁻¹, respectively, in ozonated and untreated digestates, revealing a four times higher rate of algae activity. However, this considerable higher activity was not correlated with better performance in nutrient removal since the microalgae treatment was assayed at a considerably reduced scale with a high ratio of illumination per volume. An operational costs analysis revealed that ozonation could be competitive against other strategies of color reduction such as dilution or coagulation/flocculation processes.