NOVELTY - The apparatus comprises: a membrane (10) including immobilized bacteria to produce a gas from one or more compounds in a wastewater fluid; and at least one hollow fiber (18) arranged within the membrane to convey the gas produced by the immobilized bacteria. The membrane includes a layer of a first polymer (12) in which the immobilized bacteria is immobilized. The first polymer layer is disposed between a layer of a second polymer (14) and a layer of a third polymer (16). The hollow fibers permit a passage of the gas from the first polymer layer into the hollow fibers.    USE - The apparatus or system is useful for producing a gas including hydrogen, carbon dioxide and methane from a wastewater fluid (claimed) including human waste, washing water, rainfall, industrial waste and highway drainage, where the gas is useful as a source of energy or an industrial product.    ADVANTAGE - The apparatus or system reliably produces the gas in an energy-efficient manner by immobilizing the bacteria using membrane.    DETAILED DESCRIPTION - The apparatus or system comprises: a membrane (10) including immobilized bacteria to produce a gas from one or more compounds in a wastewater fluid; and at least one hollow fiber (18) arranged within the membrane to convey the gas produced by the immobilized bacteria. The membrane includes a layer of a first polymer (12) in which the immobilized bacteria is immobilized. The first polymer layer is disposed between a layer of a second polymer (14) and a layer of a third polymer (16). The hollow fibers permit a passage of the gas produced by the immobilized bacteria from the first polymer layer into the hollow fibers. The second polymer and the third polymer are abiotic polymers. The first polymer prevents diffusion of the produced gas into the second polymer and the third polymer. The membrane has a thickness of 0.2 mm to 1 cm. The hollow fiber is a hydrophobic material or a hydrophilic material, and is potted at a first end to a first manifold and potted at a second end to a second manifold, where the hollow fiber is configured to convey the gas to the second manifold. An INDEPENDENT CLAIM is included for a method for producing and extracting a gas from a wastewater.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic perspective view of a section of a composite membrane of an apparatus for producing a gas from a wastewater fluid.    Membrane (10)    First polymer layer (12)    Second polymer layer (14)    Third polymer layer (16)    Hollow fiber. (18)