A system for biologically generating methane and removing carbon dioxide therefrom, the system comprising:
- (a) a primary anaerobic digester adapted and arranged to generate a gaseous mixture comprising methane and carbon dioxide from organic materials;
- (b) an electrochemical reactor;
- and
- (c) a hydrogenotrophic methanogenesis bioreactor adapted and arranged to convert the bicarbonate and hydrogen from the electrochemical reactor to methane;
- wherein:
- the electrochemical reactor comprises a plurality reactor cells in a stack with each reactor cell including:
- an anode;
- a cathode spaced from the anode;
- a single porous ion exchange resin wafer between the anode and the cathode, wherein the ion exchange resin wafer consists of a basic ion exchange resin wafer;
- a cation exchange membrane adjacent to the anode between the anode and the resin wafer, wherein the cation exchange membrane is adjacent to both the anode and the resin wafer;
- and
- a bipolar ion exchange membrane between the cathode and the resin wafer, wherein the bipolar exchange membrane is adjacent to both the cathode and the resin wafer;
- wherein:
- the cathode of each adjacent reactor cell is separated from the anode of the nearest adjacent cell by an electrical insulator;
- the reactor cells are in fluid communication with each other in series so that liquid and gas flow through each resin wafer sequentially;
- and
- the electrochemical reactor includes a hydrogen transfer line to direct hydrogen gas from the cathodes out of the electrochemical reactor;
- the electrochemical reactor is adapted and arranged to capture gaseous carbon dioxide within the resin wafer as aqueous bicarbonate, and to electrochemically generate hydrogen gas at the cathodes when an aqueous liquid and a carbon dioxide-containing gas are flowing through the reactor cells, and a voltage is applied across the anode and the cathode of each reactor cell;
- the primary anaerobic digester includes a gas transfer line in fluid communication with an inlet end of the electrochemical reactor adapted and arranged to receive gas and liquid into pores of the resin wafer;
- the electrochemical reactor further includes a first gas vent line;
- an outlet operably connected to a liquid transfer line in fluid communication with the hydrogenotrophic methanogenesis bioreactor;
- and a hydrogen transfer line providing fluid communication between the hydrogenotrophic methanogenesis bioreactor and a region adjacent the cathode where hydrogen is generated during use;
- and
- the hydrogenotrophic methanogenesis bioreactor comprises:
- a liquid recycle line in fluid communication with the inlet end of the electrochemical reactor adapted and arranged to direct fluid flow through the electrochemical reactor;
- and a second gas vent line;
- wherein in use, the electrochemical reactor is filled with an aqueous fluid;
- the gaseous mixture containing methane and carbon dioxide is formed from the organic materials in the primary anaerobic digester;
- and the gaseous mixture is transferred from the primary anaerobic digester via the gas transfer line into the inlet end of the electrochemical reactor to flow through the resin wafer while a voltage is applied across the cathode and the anode;
- the carbon dioxide from the gaseous mixture is electrochemically converted to bicarbonate in the aqueous fluid within electrochemical reactor;
- hydrogen is electrochemically generated at the cathode;
- the methane from the gaseous mixture and the aqueous fluid both flow through the resin wafer, and carbon dioxide-depleted methane is vented through the first gas vent line and stored for later use;
- the aqueous fluid containing the bicarbonate flows through the liquid transfer line into the hydrogenotrophic methanogenesis bioreactor, and the hydrogen generated at the cathode flows through the hydrogen transfer line into the hydrogenotrophic methanogenesis bioreactor, where the bicarbonate and hydrogen are biologically converted to methane;
- the methane generated in the hydrogenotrophic methanogenesis bioreactor is vented through the second gas vent line and collected for later use;
- and aqueous fluid is recycled back into the inlet end of the electrochemical reactor from the hydrogenotrophic methanogenesis bioreactor through the liquid recycle line.