ECE MS Thesis Defense: Jonathan Miller

ECE MS Thesis Defense: Jonathan Miller

Title: LQR-Based pH, EC, and VFA Regulation for Enhanced Microbial Fuel Cell Performance

Presenter: Jonathan Miller

Advisors: Professor Linda Doerrer & Professor David Castanon

Committee: Professor Ioannis Paschalidis

Abstract: Microbial fuel cells (MFCs) generate electricity through anaerobic microbial metabolism but require precise regulation of pH, electrical conductivity (EC), and volatile fatty acid (VFA) concentration for stable operation. This thesis develops a physics-based discrete-time linear state-space model and Linear Quadratic Regulator (LQR) for a single-chamber MFC system using two antagonistic inputs: fully fermented urine, which raises pH and EC, and pure apple juice, which lowers pH and EC while contributing VFAs. Both inputs are dosed via peristaltic pumps controlled by an Arduino GIGA R1 WiFi. The reactor is modeled as an 875 mL CSTR with states VFA, EC, and pH, where VFA is unmeasured and estimated by a Luenberger observer.

The B matrix is identified from two step-dose experiments using Nelder-Mead optimization and Differential Evolution, with the apple juice VFA contribution derived from fermentation kinetics literature. Controller performance is evaluated against a matched-volume 50:50 baseline in a repeating four-phase experiment: phosphoric acid dosing to pH 6.5, one hour of LQR control, a second acid dose, and one hour of baseline control. It is hypothesized that by maintaining pH closer to the microbial optimum of 7.0, the LQR will increase MFC output voltage and decrease ORP relative to the uncontrolled baseline.