Uncovering Process Challenges and Performance Differences for Complex Substrate Utilization in Microbial Electrolysis Cells

Microbial Electrolysis Cells (MECs) are a promising technology for sustainable energy generation. Many complex wastes have been demonstrated in MECs, however many additional wastes remain untested. To drive MECs towards commercial viability, a demonstration of each waste at high performance levels is required, and comparisons among them is required to understand their underlying limitations. This dissertation investigates the use of several complex waste streams, known as substrates, in a high performing lab scale MEC. The associated electrochemical, chemical, and biological characteristics each waste produced were then tracked. Several of these wastes are novel and have never been successfully demonstrated in MECs prior. The wastes ranged from a variety of sources, including four biomass pyrolysis aqueous fractions, oil and gas produced water, a corn stover fermentation product, and two hydrothermal liquefaction aqueous phases. Of the wastes used, produced water created the most process challenges, including calcium related fouling, film accumulation, and poor COD conversion, which were largely absent in the other substrates. Pretreatment was only required for produced water but was not required for the other substrates. By contrast, not all substrates performed well despite identical process conditions and the use of a robust anode community. The best performing substrate, the fermentation product from corn stover, lacked the recalcitrance observed in others, and had high conversion of organic material. However, other limitations associated with high performance, including mass transfer limitations, continued to affect device efficiency, as observed by increased operating voltages and pH imbalances in the anode and cathode chambers. Proton transfer percentages were observed to be high when cathode buffer was absent from MECs. Adsorption of compounds, such as phenol, were also observed, which can adversely affect performance. Adsorption as a mechanism for representing COD degradation when there is none is often neglected, and this dissertation suggests that this mechanism may be more important than otherwise assumed. Correlations between substrate performance and microbial community showed only weak association between community structure and performance, while electrochemical metrics and compound degradation rates proved to be much more closely correlated. To further characterize MECs, various ‘omics techniques will be required, as communities in MECs are shown to be capable of a wide variety of phenotypes.