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Final Report Summary - BIO-ELECTRO-ETHYLENE (Integrated Bio-Electrochemical Production of Ethylene through CO2 sequestration)

Present Marie-Curie Intra European Fellowship (IEF) Project (BIOEECTROETHYLENE - Grant No. 626959) was proposed for the CO2 reduction into acetate production. Consequently, the produced acetate was to be reduced to ethylene. Both the products were aimed to produce using specifically enriched microbial mixed consortia that was to be developed from the environmental sources.

Specific objectives Bio-Electroethylene:
• Bio-electrochemical reduction of CO2 to acetate and subsequent conversion of acetate to ethylene through integration of suitable biocathodes.
o Enrichment of electrochemically active and high efficient homoacetogenic and ethylene producing biofilms.
o Biocathodic conversion of carbon dioxide to acetate with selectively enriched homoacetogenic biofilm
o Integration ofethylene producingsecond biocathode for the conversion of formed acetate to ethylene.
• Elucidation of the mechanism for the CO2 reduction to acetate and acetate reduction to ethylene in the proposed BES with respect to the operating conditions, viz., applied redox potential, mediators, substrate, etc.
• Process economics based on preliminary results obtained from the proposed system.

Based on the objectives designed in the proposal, the project has been completed successfully with all the objectives.

During the first stage of the project the environmental samples were collected to enrich the acetate producing and ethylene producing bacterial consortia. Anaerobic sludge that treating processing waste generating from the potato processing unit was considered as the source for acetate producing bacteria, whereas soil from one feet depth of the forest near to VITO, Mol, Belgium was considered for the ethylene producing bacteria. Both the samples were individually adapted for the enrichment methodology and enriched consortia were developed.

The developed homoacetogenic bacterial consortia was used as the biocatalyst for the production of acetate from CO2. For the operational expediency bicarbonates, which is dissolved form of CO2 was used as the substrate.

Suitable electrode materials were selected for the single chamber operation of microbial electrosynthesis (MES) system. VITO-CoRE®with inert support electrode was found as suitable material for cathode and VITO-CoRE®electrode with stainless steel current collector was identified as the anode.

Single chamber operation was found to be successful for electroactive homoacetogenic biofilm development.

Maximum of 4.27 g/L acetate was produced from the 127 days of operation with an average 32% of coulombic efficiency. The carbon conversion efficiency was registered more than 90%.

Based on the conditions optimized, further, homoacetogenic bacteria evaluation for sustainable acetate production was done in dual chambered MES system. Operational parameters such as redox conditions (pH), temperature bicarbonate concentration, mode of operation were optimized.

Along with the acetate production, minute concentrations of ethanol were also produced in both single and dual chamber configurations.

It was identified that the stability of the electroactive homoacetogenic bacteria was dependent on redox conditions and product concentration in the catholyte.

An attempt was made to evaluate the bioelectrokinetics of the homoacetogenic biofilm using multiple cathodes in one catholyte chamber against large anode electrode or counter electrode in dual chamber configuration.

Hypersaline homoacetogenic consortia was sequentially developed at 15 g HCO3-/L concentration to evaluate the MES process at high inorganic carbon availability. The developed consortia was successfully developed and analyzed for the bioelectrocatalytic reduction reaction at – 800 mV and -900 mV.

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