ELECTROENZEQUEST · BioElectrochemical system for Enzyme catalyzed CO2 sEquestration for the recovery of commercially viable carbonated water and methanol

BioElectrochemical system for Enzyme catalyzed CO2 sEquestration for the recovery of commercially viable carbonated water and methanol

The current marie-curie project (ELECTROENZEQUEST) was proposed for the CO2 reduction into methanol using dehydrogenases as cascade on electrode of bioelectrochemical system. Brief objectives include • Immobilization of carbonic anhydrase (CA) on to the electrode and evaluation of its function as anode for electrogenesis in the fuel cell • Bio-electrochemical characterization of the immobilized-CA electrode and optimization of various factors influencing the functional role of CA in CO2 sequestration associated with electrogenesis • Immobilization of Formate dehydrogenase (Fate DH), formaldehyde dehydrogenase (Fald DH) and alcohol dehydrogenase (Alc DH) on an electrode and its introduction as cathode in the operating CA fuel cell • Optimization of factors affecting the fuel cell performance including the functional role of mediators such as NAD+, PQQ, etc., in mediating the electron transfer from the electrode to the substrate and in the conversion of CO2 to methanol during cathodic reduction • The bioprocess during fuel cell operation will be evaluated under optimum conditions for maximum product recovery with lowest possible energy inputs Starting with these objectives, the project was completed successfully with all the objectives. Initially, we tried to study the feasibility of conversion of CO2 into formic acid, using FateDH in free form. After analyzing the results of the first experiment, we tried to immobilize the enzyme onto electrode FateDH. After several trials, we could successfully immobilize the enzyme onto graphite based VITO-CoRETM electrode. Then, we started working on immobilization of CA along with FateDH on same electrode to increase the formic acid productivity and CO2 reduction. Further to that, we immobilized all three enzymes on a single electrode for production of methanol and CA was also added at later stage to increase the productivity. Detailed analysis of each experiment was done in comparison with controls. Immobilization in each experiment was done as follows » TBAB Modified Nafion solution was prepared for e- transfer instead of H+ transfer » Electrode to be immobilized was taken and NR was polymerized on it » Known quantity of Enzyme (one or two) was dissolved in 100 µl of PBS (pH 7,4) in an eppendorf » Added with 50 µl of modified Nafion solution . Gently vertex for 5-10 sec » Place the electrode in a petri plate and pipette out the enzyme-nafion mixture on to the electrode and let it air dried » 100 mM NaNO3 was poured on it after getting dried for equilibration Different experiments were carried out using single enzyme and multiple enzymes. All the results were consolidated and presented as a Table 1 and the Research highlights are as follows • Higher current densities due to the use of VITO based electrodes • Co-factor recycling was achieved without any secondary system • Immobilization brought stability in current densities • Conversion efficiencies based on enzyme activity are good, However, the CO2 supply can be reduced to increase the conversion rate • CA addition helped a lot in increasing the reaction rates. Solubilized CO2 can react more with the enzyme to form high product titre • Specific activities of enzyme before and after the experiment weren’t changed, which indicates the possibility of increasing the reaction time to get more product. Further experiments were continued with three enzymes (FateDH, FaldDH and AlcDH) together on the electrode, where we have observed the ethanol production from CO2 at a rate of 0.6 kg/m3/h. However, when we excluded the FaldDH also, there is no reduction in productivity of ethanol. It was surprising that we got ethanol instead of methanol but based on literature, it is also possible for the production of ethanol directly from formic acid, which is economically more viable. Further research is going on at host organization in this direction.

Data: CORDIS, © European Union