Scale-up and Measurement Enhancements of a BioGenerator Bioreactor
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.