Improving the cathode conditions by pressurizing and carbon dioxide addition to enhance the practicality of MFC treatment of wastewater

An increasing global energy demand coupled with a more rigorous governmental regulatory environment (including identifying carbon dioxide as a pollutant) is becoming more and more incompatible with engineering practices that were developed in an era of lower energy costs and less regulation. It is, therefore, not a surprise that researchers are looking towards bioelectrochemical systems (BESs) as a potential superior technology to produce environmentally-benign and sustainable energy, replace energy intensive processes, and/or produce chemical products.;The overall tenet of my thesis-based research was to understand the important mechanisms that limit the power output for BESs during wastewater treatment and to use this understanding to enhance power output and add practicality. Chapter 1 of my thesis is an introduction and shares the individual aims and organization of the thesis. In chapter 2, I evaluated the quantity of stored chemical energy in wastewater and the microbial metabolic processes, which are used to metabolize organic substrates into electricity. In addition, wastewater pre-acidification was identified as necessary to initiate waste hydrolysis into soluble substrates, which are more easily consumed by the BES anodic microbial community. In chapter 3, I developed an engineering evaluation of a laboratory-scale BES, which developed a better understanding of BES rate limitations by the ion fluxes. This work resulted in several realizations on how the BESs performance could be improved. In chapter 4, I performed a laboratory study to demonstrate that a pressurized BES cathode improved oxygen reduction reaction kinetics and increased power densities. The study also highlighted the influence of importance of transmembrane ion gradients and electroosmotic drag on the BES ion flux. In chapter 5, I used a CO2/bicarbonate buffered water process to maintain a stable acidic BES catholyte pH without adding any other buffer. This also increased the anolyte pH, alkalinity, and conductivity, which aided in a superior performance. By including the CO 2/bicarbonate buffering, the study coupled BES wastewater treatment with a potential CO2 remediation technology. Finally, in chapter 6, I summarized my findings and discussed which future activities should be performed to fasten the technology transfer of BESs from the bench to the real world.