Investigation of bioelectrochemical transport mechanisms using different microorganisms in environmental engineering applications

Considering the current state of our environment, it has become crucial to develop sustainable solutions for climate change, waste treatment and energy production. Bioelectrochemistry or microbial electrochemistry is a discipline that can progress towards these goals with the extracellular electron transfer mechanisms used in its scope. In this thesis, three related but independent studies, which can be categorized within the sub-branches of the discipline, were carried out in three different laboratories in order to contribute to the sustainability goals. These studies are respectively; "Potential role of Cable Bacteria in the chemical weathering of olivine in marine sediments for CO2 capture", "Nitrate reduction in groundwater with MFC using stabilized sludge as the carbon source for exoelectrogens" and "Decolorization of an organic dye by visible light assisted bio-photo-electrocatalysis (BPEC) system". In the first study, we have shown that cable bacteria, a microorganism capable of extracellular electron transfer at cm scale, has a potential use for capturing carbon dioxide from the atmosphere by biochemically altering the aquatic environment. In samples containing 10% and 20% olivine, pH decreased and H2S consumption increased within 2 weeks, and SiO2 accumulation was observed in the sediment after 2 cm. The results show us that the dissolution rate should be increased to increase the alkalinity concentration. In the second study, nitrate removal from synthetic groundwater was achieved by using synthetic wastewater and sewage sludge in the anode chamber. The nitrate in the cathode chamber is reduced by a first-order reaction. Electric potentials indicating the presence and activity of exoelectrogens was observed in all reactors. In the third and final study, it was observed that electrocatalysis assisted by microbial electron generation outperformed photocatalysis and photoelectrocatalysis-assisted dye removal alone. The TiO2 catalyst was reused 5 times before the decolorization efficiency was significantly dropped. Compared with the Fe3O4/TiO2 composite studies in the literature, it has been shown that the same performance is achieved by using lower TiO2 ratio under low light intensity. All the above-mentioned results show that extracellular electron transfer mechanisms are a promising technology solution with widespread use in bioelectrochemical applications.