Browsing by Author "Wuokko, Mikko"

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Chemolithoautotrophic growth of Knallgas bacteria in an electrobioreactor using in situ water electrolysis
(2017-03-30) Wuokko, Mikko
Kemian tekniikan korkeakoulu | Master's thesis
Ever-increasing amounts of carbon dioxide in the atmosphere have urged the development of efficient CO2 fixation methods. Biotechnical methods using algae and cyanobacteria have been studied, but another alternative could be the use of Knallgas bacteria. Hydrogen-oxidizing Knallgas bacteria are capable of using hydrogen as their energy source and converting CO2 into biomass. Chemolithoautotrophic gas fermentation has been studied in literature to determine the production possibilities of Knallgas bacteria. In a few studies the hydrogen and oxygen have also been produced inside an electrobioreactor, using electrolysis of the culture medium. This work established the cultivation of the Knallgas bacterium Rhodococcus opacus in electrobioreactor conditions. Several 70 ml electrobioreactor cultivations were performed to determine the suitability of the organism to the process. In the first cultivations, using platinum electrodes, it was proven that the organism was able to grow with supply of CO2, while generating hydrogen and oxygen via electrolysis of culture medium inside the reactor. Further testing using iridium oxide-coated titanium and stainless steel electrodes enabled to increase electrode surface area and current. In addition, carbonate was added in the medium to decrease the overpotential of electrolysis. Growth-improving factors were concluded to be increased hydrogen formation due to moderately higher current, and increased inoculum growth time under autotrophic conditions. Shake flask cultivations with different substrates showed that chemolithoautotrophic growth was over seven times slower than heterotrophic. Best autotrophic growth in an electrobioreactor was achieved using iridium oxide coated titanium wire as anode and stainless steel as cathode. The applied current was 14 mA in 70 ml culture volume. The maximum cell density was 3.25 g/l. The biomass composition of R. opacus was analysed, and the average protein content was 63 % of total biomass. The composition was comparable to other single-cell protein sources, as well as soybean, indicating possible uses for animal feed. The biomass-based protein price was calculated to be 3.4 €/kg, based on the electricity consumption alone. Further process improvements and cheaper electricity could result in R. opacus biomass being a viable product alternative for soybean meal as animal feed.
Jatkuvan fermentoinnin eri variaatiot fermentointitutkimuksessa
(2014-04-30) Wuokko, Mikko
Kemiantekniikan korkeakoulu | Bachelor's thesis