NOVELTY - An apparatus for biohydrogen production, comprises cell having an anion-selective membrane dividing the cell into first and second compartments. The first compartment has a cathode and second compartment has an anode, where in use the first compartment is in fluid communication with a bacterial fermentation culture and the second compartment is in fluid communication with a photoheterotrophic bacterial culture.    USE - The apparatus is useful in biohydrogen production (claimed).    ADVANTAGE - The method enables improving biohydrogen production.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) method for biohydrogen production, which involves (a) providing an apparatus comprising a cell having an anion-selective membrane dividing the cell into first and second compartments, the first compartment having a cathode, and the second compartment having an anode, (b) bringing the first compartment of the cell into fluid communication with a bacterial fermentation culture, and the second compartment into fluid communication with a photoheterotrophic bacterial culture, (c) supplying the bacterial fermentation culture with an aqueous solution of one or more fermentable carbohydrate, such that the bacterial fermentation culture ferments the fermentable carbohydrate and produces one or more organic acid, and the resulting culture medium comprises dissolved ammonium (d) supplying the first compartment of the cell with culture medium from the bacterial fermentation culture, (e) applying a potential difference between the anode and the cathode to cause an electric current to flow between anode and cathode, to cause the one or more organic acid to cross the anion-selective membrane from the first compartment of the cell to the second compartment of the cell, (f) regulating the electric current flowing between the anode and the cathode such that ammonium is transferred across the anion-selective membrane from the first cell compartment to the second cell compartment, (g) supplying the photoheterotrophic bacterial culture with culture medium from the second compartment of the cell, such that the photoheterotrophic culture ferments the one or more organic acid and produces hydrogen gas, and (h) collecting hydrogen gas produced by the photoheterotrophic bacterial culture;    (2) use of an electric current applied through the anion-selective membrane of an apparatus, to regulate the transfer of ammonium from the first cell compartment to the second cell compartment through the membrane; and    (3) use of direct electrical current to improve gaseous hydrogen production by dark fermenting bacteria capable of anaerobic fermentation of sugars to produce organic acids and hydrogen, which involves applying the current to a bacterial fermentation culture.