Comparative Study of Biocatalytic Oxidation of Some Organic Substrates Using Shewanella xiamenensis and Escherichia coli Microorganisms on Mediator and Non-Mediator Bioanodes

In the work, a comparative assessment of the effectiveness of Shewanella xiamenensis and Escherichia coli microorganisms used as a biocatalyst in the process of bioelectrochemical oxidation of various substrates in neutral media on mediator-free and mediator bioanodes was carried out. It was shown that the rate of bioelectrochemical oxidation of the studied organic substrates (citric acid, glucose, sucrose) with the help of S. xiamenensis cells does not depend on the concentration of the mediator introduced into the system (methylene blue)—electron transfer from cells to the electrode occurs as a result of direct contact of cells with the electrode’s surface. A comparative kinetic analysis showed that S. xiamenensis cells are a less effective biological catalyst for the process of glucose oxidation compared to the E. coli microorganism (in the presence of a mediator). The kinetic characteristics of the glucose oxidation reaction in the “mediator–substrate–E. coli cells” system were determined. It was found that the order of the oxidation reaction with respect to glucose at the anode is equal to one, the rate constant of this reaction is 0.0214 min–1, and the half-life of glucose is 33 min. It is shown that the model system under study makes it possible to lower the concentration of glucose in the working solution to the value of the background current, which indicates an almost complete purification of the solution from the organic substrate. It is shown that in solving practical problems in order to increase the efficiency of wastewater treatment from organic substances using mediator-free bioanodes, it is necessary to search for new cells, including other cells of the Shewanella genus, with mandatory immobilization of cells on the electrode surface in order to increase electrical contact.