Conceptual Techno-Economic Analysis of a Biomethane Plant Including Environmental Impacts: Impact of Temperature Phases and Total Solid Content

This study presents a conceptual techno-economic analysis of a compressed biogas plant in Punjab, India, examining the impacts of digester temperature phases (mesophilic and thermophilic) and total solids (TS) content on energy efficiency and economic viability. India has immense potential for utilizing its agro-residues for energy generation. However, many challenges, such as parameter control, with digester thermal management being one of the major ones, often hinder operational performance. This research evaluates six operational scenarios combining varying TS levels (10%, 20%, 30%) with mesophilic and thermophilic temperature conditions. The key metrics assessed include gross and net energy output, parasitic energy demand, thermal and electrical energy consumption, capital/operational costs, and environmental impact assessment. The results indicate that mesophilic digestion with higher TS (30%) offers the highest net energy output (234.82 GJ/day) and the lowest thermal energy demand (18.33 GJ/day), enhancing system efficiency. Conversely, low-TS thermophilic scenarios require higher heating, reducing net gains. A techno-economic trade-off is highlighted where increased TS reduces the digester volume, cost of production, fresh water demand, and the amount of liquid slurry to be disposed of. The freshwater requirement ranges from 12 to 88 L per kilogram of biomethane, depending on the TS content and slurry recirculation ratio, with a similar trend observed for liquid slurry. A substantial portion, ranging from 10% to 47% of the plant’s total energy output, is diverted for internal thermal energy consumption. Sensitivity and environmental analyses emphasize the importance of optimal TS and temperature combinations for cost-effective, sustainable operation. These findings can guide design strategies for an efficient, scalable biogas plant framework in global contexts.