A method for producing hydrogen from organic material. Organic material and hydrogen-producing microorganisms are provided in a completely mixed bioreactor for breaking down the organic material into H2, CO2, fatty acids, and alcohols. H2, CO2, and a first liquid effluent are recovered from the completely mixed bioreactor. The first liquid effluent includes hydrogen-producing microorganisms, fatty acids, and alcohols. The first liquid effluent is provided into a gravity settler for separating the first liquid effluent into a concentrated biomass (including hydrogen-producing microorganisms) and a second liquid effluent (including at least a portion of the fatty acids and the alcohols). The concentrated biomass is provided into the completely mixed bioreactor. An input voltage is applied to at least one of the completely mixed bioreactor and the gravity settler for facilitating an electrohydrogenesis process therein.