Date of Award
2006
Degree Type
Thesis
Degree Name
Master of Engineering Science
Program
Chemical and Biochemical Engineering
Supervisor
Dr. Dimitre Karamanev
Second Advisor
Dr. Kibret Mequanint
Abstract
The main of goal of this study is to improve the operation of a biofuel cell system through addressing various factors that negatively impact fuel cell operation. Firstly, jarosite precipitation creates mechanical as well as electrical resistances by depositing in the flow channels for iron and the cathode in the fuel cell. Investigation of the jarosite precipitation parameter was conducted with the classic chemolithotrophic iron oxidizing organism, Acidithiobacillus ferrooxidans. We arrived at favorable conditions of pH 1.6-1.7 and temperature of 35 °C, that limit jarosite precipitation to 0.0125-0.0209 g per gram of iron while not compromising the oxidation rate, maintained at 0.181-0.194 g∕L∙h. However, considering the low iron concentration in our experiment, this jarosite precipitation still poses a problem to our fuel cell operation, and thus a lower pH is required. This lower pH requirement is appropriate for the newly researched iron oxidizing chemolithotroph Leptospirillum sp., operating optimally at pH of 1.0. The second factor of organic metabolite accumulation was addressed by kinetically characterizing a mixotroph, Ferroplasma acidiphilum, in light that it potentially utilizes the organic by-products of chemolithotrophic growth and thus limits the organic accumulation and maintains it below the threshold lethal level of 250 ppm total organic carbon. F. acidiphilum cultured with the chemolithotroph Leptospirillum sp. at intermediate conditions was able to utilize the organic accumulation and limit the total organic concentration to 20 ppm, after initial domination by Leptospirillum. However, F. acidiphilum, like A. ferrooxidans, operates optimally at relatively high pHs in comparison 111 to Leptospirillum sp. thus rendering its use unacceptable in a biofuel cell setting due to the promotion of jarosite precipitation. Using the earlier analysis, an open biofuel cell system was operated at pH of 1.0 and temperature of 40 °C using solely Leptospirillum in order to investigate the stability of such a system and to identify further restraints. The experiment yielded steady operation at of 1.3 A, 0.65 V (0.845 W) with an oxidation rate of 1.08 g∕L∙h while maintaining high biomass concentrations of 3.3 x 109 cells/mL. Also, the total organic carbon of the system was approaching critical levels. Furthermore, the resistance of the fuel cell was increasing throughout the course of the operation due to significant jarosite deposits in the iron flow channels and cathode material, thus indicating the need for alternative operating conditions.
Recommended Citation
Daoud, Jamal Taysir, "BIOKINETIC STUDY OF BIOFUEL CELLS" (2006). Digitized Theses. 4917.
https://ir.lib.uwo.ca/digitizedtheses/4917