(91b) Technoeconomic Assessment of Emerging Technologies for the Enhancement of Anaerobic Digestion Processes at Municipal Wastewater Treatment Facilities

Treatment and disposal of municipal wastewater sludges is an expensive activity. Within the United States, 35 billion gallons of water is treated daily producing over 40,000 tons of sludge solids per day [1], costing over $50 billion for wastewater management and treatment [2]. We investigated the economic benefits of add-on technologies that can boost biogas yields from anaerobic digestion, upgrade biogas carbon dioxide to methane, and reduce the net solids to be disposed. The technology pathway was developed by Clean-Vantage, LLC and Washington State University. The investigated technologies include advanced wet oxidation steam explosion (AWOEx), carbon dioxide biomethantion, and thermophilic anaerobic digestion. The AWOEx process uses dissolved oxygen and thermal hydrolysis to transform the recalcitrant materials in biomass, boosting the net yield of methane during anaerobic digestion [3]. Methanogensis or biomethantion of the carbon dioxide in the biogas with hydrogenotrophic microorganisms can increase the net upgrading of carbon [4]. Furthermore, thermophilic anaerobic digestion can reduce the net solids while boosting biogas yield.

In this work, we modelled the installation of each aforementioned technology at a treatment facility, with existing infrastructure for mesophilic anaerobic digestion, processing five million gallons of municipal wastewater per day. The process and economic models evaluate each technology individually and as integrated systems to maximize value and minimize capital investment, operational expenses, and net greenhouse gas emissions. Our findings show that installation of all three processes results in a 59% reduction in solids to be disposed and a 352% increase in methane production. Operational costs are 40% higher with the new processes, but the revenue from the sale of renewable natural gas and the value of the associated renewable energy credits can offset the costs and generate revenue. In this presentation we will summarize the modeling approach and report the economic and environmental impacts and detail the key process sensitivities.

[1] Seiple et al., Journal Environmental Management. 197 (2017) 673-680.

[2] http://www.usmayors.org/wp-content/uploads/2018/10/2016-Spend-Article.pdf, Accessed March 2023.

[3] Dutta et al., Waste Management, 154 (2022) 105-112.

[4] Khan et al., Renewable Sustainable Energy Reviews 149 (2021) 111343.