Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Karamanev, Dimitre

Abstract

Renewable energies in the form of wind and solar have seen steadfast growth across the world, however the abundance of these technologies that demonstrate short-term variability in power output threatens power grid stability and necessitates the use of fossil fuels for rapid throttling capability. A requirement for large scale energy storage systems becomes necessary and a system based on hydrogen generation, storage, and consumption for electrical grid supply-demand stabilization using a ferric sulfate oxidant is herein explored, named the BioGenerator. As the name implies, the system functions as an indirect microbial fuel cell using a biologically active broth dominated by the iron oxidizing microbe Leptospirillum ferriphilum obtained from Iron Mountain, California.

Research into the scale-up of a pilot scale system was needed to confirm the validity of laboratory research and assess the energy consumption of the system. A conceptual energy management system is proposed based on the use of a trompe such as that of the Ragged Chute compressed air plant near Cobalt, Ontario to provide the aeration and heating requirements of the system. Novel methods of accurately measuring dissolved oxygen and volumetric mass transfer coefficient in ferric sulfate broth using microbial biooxidation stoichiometry and electrochemical amplification processes were achieved. Investigation into the direct in-situ measurement of solution pH and iron ion concentration by spectrophotometric techniques on aqueous ferric ions to reduce costs in the wear and tear of pH and redox probes was met with some success. As a result, a strategy for modelling the ferric ion absorbance characteristics has been proposed and a custom built spectrophotometer prototype was produced. Testing of a pilot scale BioGenerator yielded insights into the operating conditions that provide the best performance regarding microbial biooxidation dynamics as well as dissolved oxygen uptake and distribution within the bioreactor. Study into the search for hyperacidophiles thriving in ultra-low pH conditions revealed an interesting finding from the red algae Cyanidium caldarium that was demonstrated to show observable growth to pH -0.85 (19.5% w/w H2SO4), surpassing the current record holders of Picrophilus oshimae and Picrophilus torridus. The observation may have relevance in space exploration or genetic engineering applications.

Summary for Lay Audience

Renewable energy technology using wind and solar power is rapidly growing globally but there are issues when wind and sunlight aren’t available which can cause power brownouts which limits the amount of renewable power that can be added to the grid. A method of storing energy and releasing it to the grid as a buffer is needed to allow further expansion of renewable energy without compromising the stability of the national electrical grid. A novel energy storage system named the BioGenerator seeks to fill this role using hydrogen gas as a fuel source used in a fuel cell along with a liquid oxidant of ferric sulfate that is regenerated in a bioreactor with iron oxidizing bacteria commonly found in the flood water of abandoned mines. This technology requires research in scaling up the process from the laboratory benchtop to a pilot scale system to assess the operation more realistically and learn of any other unforeseen problems in the process of doing so. This work focuses on improving the monitoring and measurement of the liquid broth in the bioreactor to fine tune large scale construction of the bioreactor for the best energy efficiency. An energy input of low pressure compressed air is required to aerate the bioreactor and allow the bacteria inside to consume reduced ferrous iron ions in the broth, therefore reducing heat losses through exhausted air while maximizing the amount of oxygen dissolving into the broth is crucial for success of the technology and is a major focus of the study. An assessment of the overall system performance was taken to give a realistic expectation of the system in operation where previous studies had been theoretical only. Study of the limits of operation of the bacterial culture in the bioreactor was performed which led to the accidental discovery of higher than expected acid tolerance observed in an alga coexisting in the broth which was greater than the currently held record holding microbes for acid tolerance.

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