Integrating anaerobic digestion with ground source heat pump system for co-generation of heating, cooling and biogas: An economic and environmental analysis and process optimization

Integrating anaerobic digestion with a ground source heat pump system may present a new approach for providing affordable heating, cooling, and biogas to satisfy energy demands in rural regions while treating organic waste. However, research on the design and operating parameters of such an integrated system is insufficient. In the present study, a simulation model utilizing TRNSYS software has been developed and validated to analyze the economic and environmental performance of the integrated system through a combined life cycle assessment and life cycle costing methodology. The results indicate that the integrated system, which reduces total costs by 19–29 % across various operational temperatures, displays superior overall performance compared to the standalone system. When the anaerobic digestion subsystem operates year-round at mesophilic temperature (37 °C), the coupling system offers substantial financial and ecological advantages over thermophilic (55 °C) and psychrophilic (26 °C) anaerobic digestion. However, if the biogas selling price exceeds 1.4 CNY/m3, it is recommended that the anaerobic digestion subsystem adopt thermophilic anaerobic digestion during transitional seasons and mesophilic anaerobic digestion in winter to achieve better overall performance. Additionally, an optimal drilling depth of 60 m was identified, which reduces costs by 11 % compared to a depth of 100 m.