Enzyme, Electrode and Reactor Design for Enzymatic Cascade Reactions

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The objective of the proposed project is to develop an enzyme-based bioelectrocatalytic nitrate ammonification system (also known as dissimilatory nitrate reduction to ammonium, DNRA) that quantitatively transforms nitrate into nitrite and further into ammonium, at first separately but ultimately in an integrated setting. For this, nitrate reductases and nitrite reductases will be coupled with tailored 3D-porous electrodes and integrated into advanced bioelectrochemical reactors to achieve high conversion rates. The enzymes will be engineered for high activity and stability as well as efficient electrode attachment (electrostatics, coordination, covalent binding). Tailored 3D-porous electrode materials and electrodes compatible with in-situ spectroelectrochemistry methods will subsequently be developed and finetuned in terms of enzyme immobilization (adsorption and desorption studies) and protein film voltammetry (direct versus mediated electron transfer). Finally, high performance electrochemical zero-gap cells will be designed that allow for high current densities and electrode integration will be realized with promising enzyme-electrode combinations that are evaluated for continuously operated single reactor reactions. Once the materials, immobilization strategies and reactor designs are optimized, integrated systems for enzymatic cascade reactions will be developed. Depending on the respective reaction kinetics of the single enzymes, parameters such as enzyme loading, co- versus layered immobilization, and electrode thicknesses will be varied, aiming for complete substrate conversion and long-term stability.