بررسی پایداری تولید بیوگاز از پسماند گندم: از دیدگاه ارزیابی چرخه حیات

Introduction
Life cycle assessment (LCA) quantifies and interprets environmental impacts across a wide range of products or processes used throughout the system. Despite the need to understand regional differences in the life cycle assessment of agricultural systems, the LCA method is poorly defined due to regional heterogeneity modeling in agricultural production and transportation. Therefore, there is an opportunity to help develop LCA protocols by adapting methods commensurate with crop production and supply chain changes. The annual balance in soil organic carbon is a function of three main processes: stabilization in plant biomass, plant, soil, rooting, and long-term storage in soil. According to Kozyakov, a comprehensive review of the carbon cycle, approximately half of the total carbon dioxide absorbed from the atmosphere by the wheat plant is converted to biomass. This study aims to evaluate the impact of using wheat waste for biogas production on the environment and greenhouse gas emissions. This research's life cycle inventory includes the production of wheat waste and its use in biogas production. Many studies have been devoted to discovering the effects of these various variables, particularly in terms of global warming and nitrogen fertilizer leaching, and based on such comprehensive information, a Life Cycle Assessment has been proposed to assess the cumulative environmental impacts of agriculture. The challenge for these tools is to be relevant both on a global scale, ie for global impact categories such as climate change, and on a smaller scale, i.e. for regional impact categories such as water eutrophication. The International Organization for Standardization and the Society for Environmental Toxicology and Chemistry provided an overview of the LCA method. However, the main issues under discussion are life cycle assessment methods, aggregation methods for different impact groups, and the final calculation of a summary environmental indicator. Next, inventory analysis continues with impact assessment.

Methodology
This case study examines regional changes in field straw production and crop transportation for wheat using life cycle assessments and compares the results with carbon cycle estimates. Wheat is used as an agricultural product because it is the third-largest crop in terms of volume and value and grows in almost many parts of Iran. Life cycle assessment is different from previous studies and emphasizes the use of fuel, fertilizer, yield, and transportation throughout the country in the emission of greenhouse gases in agricultural methods and tries to spatially and different types of production. Wheat is independent. This case study can be partially supported and pursued by research centers for life cycle assessment, which are interested in conducting environmental studies in wheat production. Many of the wheat's share is imported, influencing domestic food systems policy.
The study area is Iran, with a share of about 2.2 percent of world wheat production, is ranked 14th among twenty wheat-producing countries. According to the Food and Agriculture Organization of the United Nations (FAO), China ranks first in 2019 with 131 million tons of wheat production. India follows it with 99.7 million tons, Russia with 72.1 million tons, the United States with 51.3 million tons, and France with 38.5 million tons. It is noteworthy that among the countries in the region, Pakistan, with a production of 25.1 million tons (1.8 times more than Iran), in the seventh place in the world, and Turkey with a production of 20 million tons of wheat (1.5 times more than Iran) in the eleventh place in the world are located. Figure 2 shows the complete map of wheat production in Iran. According to statistics, the highest wheat production (rainfed and irrigated) is related to the cities of Shousha, Marvdasht, and Ahvaz, with an approximate share of 2.3% of the total 84% of wheat production. Bilesvar city in Ardabil province is ranked eighth in the country with a share of 1.5 percent of total wheat production.This study aims to determine the amount of biogas production from wheat waste. Due to climatic conditions, the study area can produce biogas from wheat waste (as carbon waste). The amount of wheat waste used in biogas production varies. For biogas production, the combined presence of nitrogen and carbon is necessary to regulate C / N, which is an essential parameter in biogas production. Various studies have been conducted in the field of biogas production. In a study conducted by Jafari et al. (2019), in the conventional biogas production method, the share of wheat waste in the total amount of substrate was considered to be about 45% of the total material. According to the findings, the highest impact is related to the Aquatic ecotoxicity index with 24.63. The lowest level is related to the Ozone layer depletion index with a value of 0.0000000264. Table 3 presents the damage caused by consuming one kilogram of wheat straw for biogas production on the final indicators. According to the final indicators, it can be concluded that the lowest impact on the final indicators for the consumption of wheat straw as a substrate for biogas production is related to the Human health index with an approximate value of 0.000000342. The highest impact is related to the index related to Resources with The value is approximately equal to 3.26.

Conclusion
In this study, the effects of fermentation of wheat waste for biogas production were investigated in a comparative format for environmental indicators. In general, it can be claimed that the lowest impact on the final indicators for the consumption of wheat straw as a substrate for biogas production is related to the Human health index with an approximate value of 0.000000342, and the highest effect is related to the Resources index with an approximately equal value. In general, the environmental effects of wheat consumption as a substrate for biogas production are higher than the impact of wheat straw and grain production on some intermediate indicators. Another scenario could be proposed to prevent methane from entering the atmosphere directly. This procedure is also accurate in the final indicators. The release of methane into the air increases the environmental impact because, according to various sources, the impact of methane on global warming is several times greater than the impact of carbon dioxide on global warming. Therefore, there is a need for a consumption scenario after biogas production to prevent methane from entering the atmosphere.