عنوان مقاله [English]
Livestock waste is the most suitable material for biogas production, but it is not always the best material. If cows are kept on a farm with a burial system, collecting their feces for biogas is very easy. While usually, in Iran, farms are traditional and even live in rangeland in some months of the year. As a result, it is likely to have to be collected from the ground to obtain fertilizer, which increases the workload for biogas production. Otherwise, the substrate remains in the new range. Other parts of the plant can also be used, such as wheat straw, unless they have a high lignin content. Development in rural areas has suffered from armed conflict for the past 100 years, and people have fled to neighboring cities or countries. In some villages in northwestern Iran, the gas pipeline network is not extensive. Liquefied natural gas transportation is a solution for transferring energy to remote villages. Extensive use of firewood for energy purposes also severely impacts local forests. This phenomenon is one of the main reasons for increasing greenhouse gas emissions, deforestation, and land degradation. It is estimated that replacing these heat generation methods with biogas digesters can significantly contribute to the production of pollutants, land and forest degradation, and the prevention of environmental pollution. The situation is similar in arid and semi-arid regions of Asia. There are many benefits to using biogas as an energy source. Efficient, reliable, cost-effective, and environmentally friendly. In most rural areas, home cooking is cooked on a conventional stove or traditional stove, where the biomass is burned directly, leading to further emissions of carbon monoxide and hydrocarbons. Indoor air pollution primarily affects women and children because they are usually responsible for cooking and spend much time in a smoke-contaminated environment, leading to serious health problems such as lung cancer, pneumonia, or other lung diseases. Be. This study aims to set up three different possible scenarios for a small-scale biogas digester in different regions of northwestern Iran with low technology. The use of ubiquitous biomass such as cow manure as a base, kitchen waste (medium fat), potato peel, or wheat straw helps obtain a constant gas throughout the year without the need for ample storage as substrates. These resources are provided daily and are available for a long time. In addition, greenhouse gas emissions are calculated for each scenario to show the difference in carbon footprint compared to using firewood or liquefied petroleum gas for cooking instead of biogas. Finally, the usefulness of the by-product, fermented litter, is also an important point to check its usability as a plant fertilizer. This study helps to map out the future of small-scale biogas digesters in rural, mountainous areas.
In order to calculate the specific emissions of biogas emissions, the standard method of life cycle assessment (LCA) was used using the SIMA PRO tool. This study aims to provide special effects on global warming/greenhouse gas reduction in production and the use of biogas as an energy source. Therefore, helpful energy was used as the functional unit of one megajoule. The system boundaries are shown in Figure 1. For biogas systems, life cycle inventory (LCI) is collected from the LfL biogas database.
The selected beds represent the typical waste of rural households in northwestern Iran. Most farmers in these areas have dairy cows, so choosing cow manure as the primary substrate is a logical consequence. This substrate can be removed directly from the farm or must be collected from the pasture ground and then mixed with water 50:50 to obtain a homogeneous liquid to feed the biogas digester. Where people cook, waste is generated; here, we look at medium-fat kitchen waste as an input option for the fermenter. A unique waste product of daily cooking is potato skin because potatoes are considered the leading food in northwestern Iran and other parts of Iran. The common substrate for the third scenario is wheat straw after harvest and wheat processing. Instead of not using it or using it poorly, a more efficient way is to extract the biogas by cutting it into small pieces and fermenting it. In short, all materials are available all year round, and if they are not used to produce biogas, they have no or little use.
According to the presented results, significant differences in the gas output of the three modes are detectable and are shown in Figure 2. The second scenario with 70% cow manure and 30% potato skin shows the lowest biogas production per year with 69.6 square meters. With an annual biogas production of 76.3 square meters, the first scenario is currently more productive than Scenario II, but the third scenario has the highest biogas output. This modulation, including 60% cow manure and 40% wheat straw, produces 94.2 square meters of biogas per year and is the most efficient of the three scenarios. The first scenario emits the lowest CO2 equivalent with 0.236 kg, and the third scenario emits the highest CO2 equivalent with 0.333 kg CO2 equivalent. Because biogas emissions are pretty similar (0.151-0.182 kg equivalent to CO2), the value of machinery and equipment varies between 0.070-0.155 kg equivalent to CO2 in three scenarios. However, unlike the fossil fuel source, which often uses LPG and NG, biogas scenarios do much less damage to the climate than this fuel. Greenhouse gas emissions are 1.59 kg, equivalent to CO2. Which is much larger than biogas; Figure 2 shows the total gas production, while the critical part is the methane content because methane represents the energy content of the gas. Most digesters must be built for direct gas use and direct gas combustion in northwestern Iran for cooking purposes. Therefore, methane analysis is a significant concern in this area. The blue bars in the diagram (Figure 2) show the total biogas production of each scenario. Therefore, the direct use of methane produced by the fermentation process and biogas production (rather than releasing it into the air) will be an essential factor in reducing the environmental impact of the biogas produced.
Biogas has already proven its potential to become a successful model for sustainable energy production in other countries. Its environmental, social, and economic benefits are visible to users and all countries. In northwestern Iran, employment in rural communities can be created by establishing local cooperatives to install and maintain biogas production systems. Women become empowered because they no longer suffer from air pollution. Because fuel and fertilizer costs are reduced entirely or at least in large part, biogas means financial support for families in the long run.
However, budget is a significant constraint on progress in implementing biogas in rural areas. In most countries, installing a digester for subsistence farmers without subsidies is neither cost-effective nor sustainable. More solutions and options to reduce the cost of digestive systems must be developed for each country to reach the goal of 2030, namely green energy for all. Evaluating carbon emissions trading or other sustainable subsidy mechanisms can help make biogas more cost-effective. Asset costs prevent the spread of biogas systems and the lack of knowledge. Therefore, investing in education is very important to increase the interest in biogas among the people. Rural communities need to be more involved with this technology to understand it as a good energy source for their families. More research needs to be done because there is almost no biogas database in Iran.