عنوان مقاله [English]
Iran is very rich in fossil fuels such as coal, oil, and natural gas. After fossil fuels, biomass is the fourth source of sustainable energy in Iran and around the world. Biomass resources include a wide range of organic materials, which are mainly divided into six groups: 1) wood, 2) waste collected from the forest and agriculture, horticulture, and food industries, and 3) garbage. urban solids, 4) sewage, 5) animal waste, 6) sewage, and industrial organic waste. The direct use of these sources can produce heat and if they are used to produce biofuels such as biogas, which can be used in engine generators to produce electricity. On the one hand, Iran benefits from non-renewable fossil fuel sources such as oil and gas, and on the other hand, this country has unlimited potential for sustainable energy sources such as the sun, geothermal, wind, hydrogen, and biomass. also benefits. In fact, renewable energy sources are becoming more popular day by day. The human population will soon be deprived of non-renewable energy sources. Perishable materials and solid waste (biomass) are abundant, and the operation of the biogas system is very simple, therefore, many countries, including China, Germany, and Sweden, have requested to produce more bioenergy. Nowadays, much attention is paid to renewable energies. Several studies have been conducted in relation to biogas production and GHG reduction. Carbon dioxide (CO2) is the most important factor among all the greenhouse gases released during fossil energy production. This study is an introduction to the sources, status, and prospects of food waste as the main biomass in the direction of sustainable biogas energy production in Iran. This study consists of five stages. In the first step, we present an introduction to the overview of the research. In the second stage, we discuss the production of biogas and the amount of biomass production and also measure the production and consumption of energy. In the third stage, we discuss the reduction of pollution caused by greenhouse gases. In the fourth stage, we observe the plan from an economic point of view and finally provide a comprehensive conclusion of the issue.
In this study, food waste was used as the main biomass material for biogas production. The required food waste was obtained from the canteen of Mohaghegh Ardabili University located in Ardabil province. To measure the initial moisture content of food waste, 100 grams of food waste was placed in the oven for 24 hours and weighed again. The difference in weight showed the amount of moisture in food waste. Total solids (TS) were determined by subtracting the amount of moisture from the total amount of food waste. Volatile solids (VS) were also determined by burning 5 grams (TS) at 550°C for two hours in an electric oven based on the American Public Health Association (APHA) standard. The amount of nitrogen in the biomass and the level of organic carbon were in accordance with the APHA standard using the Kjeldahl and chemical burning methods. Digesters were placed in a hot water bath at a temperature of 35 degrees Celsius. Temperatures were measured and controlled using a digital thermostat with an accuracy of ±0.1°C. The biogas produced from the digesters was transferred to another set of plastic bottles and their volume was measured using the water displacement method. The produced biogas was transferred to NaOH solution and after absorbing CO2 and H2S, methane was extracted and its percentage was calculated using the displacement method with an accuracy of ±5 ml. The experimental results of this study show that the amount of biogas produced at a temperature of 35°C is equal to 314.11 L/kg.VS and at a temperature of 55°C it increases to 8.364 L/kg.VS. It is about 17.7% of the total VS, so, for 12 tons of waste, VS is equal to 2.124 tons. In this way, the reduced volume of biogas is 667.19 cubic meters. Assuming the low heating value of biogas (18 MJ/m3), the total heating value of produced biogas will be 3335.48 kWh. The energy produced in a period of biogas production, with the amount of 12 tons of waste, will be 277.95 kW.h/ton at a temperature of 35 degrees Celsius and 322.84 kW.h/ton at a temperature of 55 degrees Celsius. The main challenges in ensuring energy security are the use of economic production resources. Currently, the cost of producing energy from biogas is slightly higher than other types of energy due to the technology used in it.
Based on calculations, biogas produced from 12 tons of waste is about 667.19 cubic meters. If the percentage of methane in biogas is considered to be 60%, the total amount of methane produced is equal to 400.3 cubic meters. The price of 1 cubic meter of natural gas in Iran is about $0.05. Therefore, the income from the sale of biogas will be $20, which is a small amount, but the remaining sludge in the digester, which is sold as nitrogen-enriched fertilizer, has more customers in the agricultural and horticultural sectors. It can be predicted that after the fermentation operation in each period of biogas production, about 11 tons of wet fertilizer with 80% humidity will be obtained, which is equivalent to 6.6 tons of organic nitrogen fertilizer with 40% humidity. Currently, the price of organic fertilizers in Iran is 25 dollars per ton. As a result, the income from the sale of organic fertilizers is about 165 dollars per production period.
In this study, methane fuel produced from food waste was proposed as an alternative source of natural gas fuel. Therefore, according to the calculations made in this research, by replacing produced methane with natural gas, about 4517.6 tons of carbon dioxide was released into the atmosphere. Considering the concerns about global warming and the commitment of countries to reduce greenhouse gas emissions according to the Paris Agreement, it can be said that the use of produced biogas can be beneficial. Economic calculations showed that considering all the income from the sale of biogas and fertilizer and the amount initial cost and maintenance cost of biogas production, the initial investment cost to make biogas from food waste can be returned after 36 months after the return. Biogas production and the system will serve as a source of the net and sustainable income for its owners. This case is valued when it can be claimed that the security of biogas energy production depends on the security of providing its raw materials, and with a very simple system, it can be presented as a source of sustainable production, especially in remote areas, so that It reduces the cost of energy transmission to remote points and is also considered important from the point of view of passive defense. So that in case of damage to the overall energy transmission network, the cycle of energy production, transmission and consumption operates in a completely independent and location-oriented manner and maintains the stability of the entire network.