Surveying the applicability of energy recovery technologies for waste treatment: Case study for anaerobic wastewater treatment in Minnesota

Waste treatment is an important part of the future global energy portfolio. Challenges associated with implementing energy recovery technology at waste treatment sites include interwoven technical, economic, and policy considerations. This work focuses on the tradeoff of input waste energy content to output electrical power, i.e. efficiency for waste-to-energy systems. Also presented is an approach for conversion technology selection based on characteristics of the waste stream, energy content of biogas generated from anaerobic waste treatment, and commercial applicability of five major prime movers across a large gradient of power output including: gas turbines, steam turbines, microturbines, reciprocating internal combustion engines, and solid oxide fuel cells. An efficiency model developed from fundamental thermodynamic principles is used to estimate the amount of power available from a waste treatment site, using data from a comprehensive data set of prime mover characteristics. A case study is presented, illustrating prime mover selection for three types of waste systems in Minnesota, United States: wastewater treatment plants, landfill sites and dairy farms. The results show that gas and steam turbines are recommended for large-scale systems with millions of gallons per day of wastewater generation, up to 60% of waste treatment sites. For small-scale systems applicable to distributed waste treatment and wastewater treatment facilities processing less than 10,000 gallons of water per day, fuel cells are recommended solely based on their high efficiency. Given the potential growth of decentralized waste-to-energy, the scarcity of highly efficient, affordable and fuel flexible power generation options necessitates further innovation in small-scale prime mover technologies. Implications: Energy recovery from waste has not reached its potential due to several decision-influencing factors and technical challenges. Here an efficiency model is presented that theoretically validates efficiency curves for prime movers often shown in previous literature, but without physical verification. The developed regime model has significant practical utility as it concisely estimates power generation potential of a given waste treatment site. This work decouples decision factors by providing a practical template to better identify applicability of a prime mover to waste processing scenarios. In addition, the applicability analysis highlights areas in need of innovation, technology, and policy to address the changing landscape of waste treatment scale and potential opportunity to recover energy from small-scale distributed treatment facilities.

Automated summary

Waste treatment plays a crucial role in the future global energy portfolio, but implementing energy recovery technology faces challenges in technical, economic, and policy aspects. This study focuses on the tradeoff between input waste energy content and output electrical power efficiency, as well as the selection of conversion technology based on waste characteristics and energy content. Case studies suggest that gas and steam turbines are recommended for large-scale systems, while fuel cells are suitable for small-scale systems based on their high efficiency.