An electrodeionization device includes a deionization chamber partitioned by a pair of ion exchange membranes; and a concentration chamber disposed adjacent to the deionization chamber via the ion exchange membrane which is disposed on a side facing a cathode. When representing a particle size of 0.1 mm or more and 0.4 mm or less by small particle size; and a particle side exceeding 0.4 mm by large particle size, a large particle size layer consisting of an ion exchange resin of large particle size, and a mixed particle size layer in which ion exchange resins of large particle size and small particle size are mixed are arranged in the concentration chamber along a flow direction of water to be treated. At least a part of the ion exchange resin filled in the concentration chamber is a cation exchange resin.

A system for biological methane production and removing carbon dioxide from the methane comprises (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 comprising at least one reactor cell including an anode spaced from a cathode by a porous ion exchange resin wafer with a cation exchange membrane between the anode and the resin wafer and a bipolar ion exchange membrane between the cathode and the resin wafer; the electrochemical reactor being adapted and arranged to capture gaseous carbon dioxide within the resin wafer as aqueous bicarbonate, and to electrochemically generate hydrogen gas at the cathode; and (c) a hydrogenotrophic methanogenesis bioreactor adapted and arranged to convert the bicarbonate and hydrogen from the electrochemical reactor to methane. An electrochemical reactor and a method for producing methane with reduced carbon dioxide content also are described.

An electrodeionization device includes a spacer comprising a first inlet port, a first outlet port, a first plurality of first flow channels configured to direct fluid in a first direction from the first inlet port to the first outlet port, and a second flow channel in series fluid communication with the first plurality of first flow channels between the first inlet port and first outlet port and configured to direct fluid in a second direction different from the first direction from the first inlet port to the first outlet port.

A water treatment apparatus for removing dissolved oxygen contained in water to be treated includes: an anode; a cathode; and a dissolved oxygen removal chamber which is located between the anode and the cathode and filled with an ion exchanger. At least a portion of the ion exchanger filled in the dissolved oxygen removal chamber is an ion exchanger on which a metal catalyst is supported. The ion exchanger on which the metal catalyst is supported is filled in a single bed configuration in at least a portion of the dissolved oxygen removal chamber. A DC current is applied between the anode and the cathode.

A device for removing ions from a solution. The device includes first and second intercalation hosts, an anion exchange membrane, a first compartment extending between the first intercalation host and the anion exchange membrane, and a second compartment extending between the second intercalation host and the anion exchange membrane. The first and/or second intercalation hosts include a mixture of first and second intercalation materials. The first and/or second intercalation hosts may include layers (e.g., alternating layers) of the first and second intercalation materials. The first and second intercalation materials are different.