COMPARATIVE ENERGY EVALUATION OF MACRONUTRIENT AND MICRONUTRIENT USE IN CORN-BASED BIOGAS SYSTEMS

Energy assessment has emerged as a more objective and reliable approach to evaluating biogas production technologies compared to traditional economic analysis, which is often influenced by political and social factors. This study investigates the energy efficiency of biogas production from corn cultivation, with particular attention to the allocation of energy costs between methane and biofertilizers obtained through fermentation. Results show that the energy efficiency coefficient, defined as the ratio of energy derived from methane to the energy invested in corn cultivation, harvesting, and processing, ranges between 2.9 and 5.1. Energy expenditures for corn cultivation were estimated at 25.3–63.8 GJ/ha or 0.8–1.4 GJ/t of green mass.

The application of macronutrients (NPK fertilizers) significantly increased energy costs, leading to a reduction in energy efficiency. For instance, the use of N90P60K60 raised energy expenditures by 34.8–53.0% compared to unfertilized variants, while N120P90K90 required an additional 36.2–43.9%. In contrast, micronutrient treatments slightly increased energy costs (3.2–7.3%) but improved methane yield, thereby enhancing overall efficiency. The highest methane energy output (207.5 GJ/ha) was recorded in the hybrid Carifols under intensive fertilization and seed treatment, whereas the highest energy efficiency coefficient (5.1) was achieved in the hybrid Bogatyr without macronutrient application.

These findings highlight the trade-off between maximizing methane yield and maintaining high energy efficiency. While intensive fertilization strategies can boost energy output, they simultaneously reduce efficiency due to higher energy inputs. Conversely, variants without macronutrients demonstrate superior efficiency, underscoring the importance of balancing fertilizer application strategies to optimize both yield and sustainability. The study provides valuable insights for designing energy-efficient biogas production systems, emphasizing the role of nutrient management in achieving sustainable bioenergy outcomes.