Date of Award

6-13-2023

Document Type

Thesis

Publisher

Santa Clara : Santa Clara University, 2023

Departments

Bioengineering

First Advisor

Maryam Mobed-Miremadi

Abstract

Microbial fuel cells (MFC) are a rapidly growing field of interest with potential for clean energy production, effluent/waste capture and purification. Drawbacks associated with MFCs is the short duration of the peak current, discouraging integration into emerging nanogrids, as well as the operational cost associated with the infrastructure, offsetting the net cost of power generation. With the objective of quantifying the success of genetic mutations using the MFC to address the above-mentioned problem-solving opportunities, the following specific aims were formulated in this study: 1) To measure current as a metric for growth/catalytic activity for microencapsulated microorganisms, and, 2) To optimize the operating parameters in the microbial fuel cell run in batch mode, namely the baseline noise. A benchtop commercial MFC was characterized by measuring the growth of the non-exoelectrogen Saccharomyces cerevisiae in free and immobilized in millimeter thick alginate slabs coated with chitosan. Metrics for benchmarking the prototype encountered in peer-reviewed literature were used to rate the current vs time curves for a 2-hour run. The metabolic behavior of microencapsulated yeast (2.5 g dry cells in encapsulated 2% sterilized medium MW alginate) grown on 0.5 M sucrose, displayed the highest peak/average currents (500 μA/300 μA), area under the curve (AUC=2.75A), and peak current per anode surface area (64.1 μA /cm2) as compared to the baseline buffer and empty biopolymer slabs. Meanwhile, the comparison of the free vs. immobilized was hindered by the high noise measured immediately after substrate injection and fast growth peak as hypothesized during the formulation of the proposed specific aims. For robust replication, optimization techniques were explored in an L 16 (4 5) Taguchi design including cell concentration [X], sucrose concentration [S], dry cell grain size, alginate concentration and chitosan coating time. An earlier subset of the results indicated that the variables above from which the inner matrix was comprised were not sufficient to predict the surface response. Next, the performance of lag phase non-encapsulated E. coli DH5α transformed with the pKAU17 plasmid vector to express the enzyme urease and degrade urea as a source of ammonia fuel was initiated in uremic and non-uremic media. Results were inconclusive with possible factors to be optimized  being the cytotoxicity of the mediator methylene blue and the high noise associated with  the non-immobilized, non-exoelectrogenic microorganism to be studied in future efforts.

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