A Bug’s Life: Integration of Anaerobic Digestion and Bioelectrochemical Systems for Enhanced Energy Recovery from Wastewater Solids and Other Waste Substrates

Organic waste streams, like domestic wastewater and municipal solid waste, have the potential to be used as feedstocks for biotechnology processes to produce high value products and energy. This thesis investigated the technological, economical, and environmental potential for integrated anaerobic digestion (AD) and bioelectrochemical system (BES) platforms as they were theoretically and physically evaluated for energy recovery from domestic wastewater. The first chapter of this thesis compared the theoretical energy efficiencies of converting waste directly into electricity, using AD and BES alone and in various combinations. This chapter reviewed the experimentally demonstrated energy efficiencies reported in the literature with comparisons to the maximum theoretical efficiencies, considering thermodynamic limits. Acetate was used as an ideal substrate for theoretical calculations, whereas complex wastes were used for extended analyses of practical efficiencies. In addition, to address the potential economic and environmental benefits of this technology, a brief case study was investigated using the Oak Ridge National Laboratory (ORNL) water resource recovery facility (WRRF). This work identified a combined Anaerobic Digestion/Microbial Electrolysis Cell (ADMEC) platform as the most viable treatment process for further study. In the second chapter, the abovementioned ADMEC system was tested using real domestic wastewater from the ORNL WRRF. The system was modified to include two pretreatment methods, alkaline and thermal hydrolysis, to observe potential effects of pretreatment on energy recovery. The systems in chapter two were operated so that hydrogen recovery was maximized, at the expense of biogas recovery. The results from this chapter indicated that thermal hydrolysis pretreatment had the greatest positive effect on methane composition and hydrogen production, while also reducing overall biogas production. Alkaline pretreatment had a net-negative impact on energy recovery compared to the control. This thesis concludes with my personal reflection on these technologies and where I think they may play a role in the future.