Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Dr.Dimitre Karamanev

Abstract

For the time being transfer from the fossil fuel powered electricity generation technologies to renewable sources is facing a great deal of challenges, because of their intermittent nature. Efficient ways of electricity storage are essential to make it happen, and our electro-biotechnology - the BioGenerator - may be a potential solution, due to its uniqueness consisting in employing iron oxidizing microorganisms. This work presents a scale-up of the BioGenerator from 1W to 300W capacity in a stepwise manner. It involved the design, study and scale-up of the airlift bioreactor from 1.4 to 600 L, and electrochemical cells with different catholyte flow patterns from 4x4 cm (1.6 W) to a stack of 20x20 cm cells (271 W). An impact of different operating regimes and the catholyte characteristics on the electrochemical cell performance was studied. Based on the experimental results collected over the course of this Ph.D. research project, the largest and most advanced system to date - 10 kW BioGenerator - was designed and currently is under construction.

Oxygen mass transfer and microbial dynamics in the large-scale bioreactors (400 and 600 L) were studied and extraordinary resilience of L. ferriphilum dominated culture was observed. It was found that it takes ~5.5. days for the bacteria to recover and resume their iron oxidizing ability even after 5 months of starvation.

An array of commercially available proton exchange membranes was tested in terms of their suitability for the use in the BioGenerator, and Selemion HSF was found to be the best amongst them. The straight forward techniques for the synthesis of Nafion- and polyvinyl alcohol (PVA)-based membranes were proposed. The proton conductivity, water transport and ferric ion diffusion through the synthesized membranes were measured. Testing in the Fe3+/H2 electrochemical cell revealed that the most promising, in terms of both performance and economics, amongst them is a phosphorylated PVA membrane.

A mathematical model describing the operation of the BioGenerator system was developed and successfully tested during validation experiments. The data predicted was in a fairly good agreement with the experimental.

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