Introduction: Biogas is a natural and cost-effective source of energy that leaves significant impacts on the environment and industries, widely produced and utilized in many countries. This gas is generated through the anaerobic digestion of organic materials, including animal manure, food waste, and sewage. Microorganisms play a crucial role in the biogas production process by feeding on biomass. The digestion carried out by these microorganisms produces methane, constituting approximately 50-70% of biogas, which is flammable and used for cooking, cooling and heating, electricity generation, methanol and steam production, waste management, and mechanical power. Given these benefits, biogas production holds special significance, and extensive research has been conducted globally in this field, yielding valuable results. In the present study, we aim to investigate and evaluate the influence of lentil skin as a biomass on the quantity and constituents of produced biogas.

Materials and Methods: This research was conducted in the Biosystems Mechanics Workshop of the Faculty of Agriculture, Ilam University. The objective of this study was to investigate the effect of lentil skin on biogas production and analyze its constituent components. The workflow typically comprised four stages. In the first stage, fresh lentil skins were broken down into smaller pieces and stored in a suitable environment to be used as digester feedstock for the experiment. Shredding organic waste aids in the digestion process. The second stage involved providing optimal conditions for microbes, which require warmth. Accordingly, the temperature was maintained at an average of 28-30 degrees Celsius during the experiment.
The third stage involved the actual digestion process, where anaerobic digestion took place in large tanks, resulting in real biogas production. For this purpose, materials were combined in predetermined proportions (1:1) and loaded into the digesters. In each stage, 5 kilograms of lentil skin were combined with 5 kilograms of water and added to the digester. The experiment was conducted in three repetitions, employing fixed digesters, digesters with agitation every three days, and digesters with daily agitation as influencing factors. The quantity of biogas production and its components were examined over a 30-day period. Gas sampling occurred every 10 days, while pH and gas pressure were measured every 72 hours. In the final stage, the gas underwent purification by removing impurities and carbon dioxide. The amount of gases produced from lentil skin was measured using a chromatograph with a TCD detector. This instrument employs chromatography-based separation. It's worth noting that 9 gas capsules specifically designed for automobiles were used to construct the digesters. The construction stages of the digesters included cleaning, coloring, and installing connections. Moreover, to create uniform temperature and concentration conditions inside the tank, inlet and outlet connections were carefully designed and installed. A safety valve was also installed to ensure the safety of the digesters.

Results and Discussion: The obtained results, including loading conditions, pH levels, and internal pressure within the digester during the experiment, and the quantity and components of biogas, were examined across all samples. Statistical methods, including Analysis of Variance (ANOVA) and Duncan's mean comparison test, were employed for data analysis. The results indicated that digester agitation directly influences the pH levels, with the highest pH observed in digesters with daily agitation, displaying the most significant fluctuations. Furthermore, digester agitation has a direct impact on the biogas production levels, enhancing structural effects within the digester. However, frequent agitation repetition has a negligible effect on the amount of biogas produced. The average methane production rates in this process were 34.06% mol for digesters with daily agitation, 23.09% mol for digesters with agitation every three days, and 17.32% mol for fixed digesters.

Conclusion:  Currently, a significant portion of the world's energy demand is met through fossil fuels, the combustion of which releases carbon dioxide and various pollutants, including sulfur and nitrogen oxides, which are highly harmful. Consequently, in recent years, there has been a growing inclination towards utilizing various renewable energy sources. One crucial energy source that also provides a solution for waste reduction is biogas. Given the increasing importance of sustainable energy development and the need for waste management, anaerobic digestion technology and biogas production have rapidly grown. Therefore, the findings of this research underscore the importance of exploring innovative methods and utilizing diverse biological resources in managing and optimizing the biogas production process.