A method for producing H2, methane, VFAs and alcohols from organic material, including the steps of introducing organic material and microorganisms into a completely mixed bioreactor for producing H2, CO2, VFAs, and alcohols; recovering H2 and CO2; recovering a first liquid effluent including microorganisms, VFAs, and alcohols; introducing the first liquid effluent into a gravity settler for separating into a first biomass including microorganisms and a second liquid effluent including VFAs, alcohols and microorganisms; introducing the second liquid effluent into a separation module for separating into a second biomass including microorganisms and a third liquid effluent including VFAs and alcohols; recovering at least a portion of the third liquid effluent; and providing a recovered biomass by recovering at least a portion of the first biomass, the second biomass, or both, and introducing the recovered biomass into a biomethanator for production of CH4 and CO2.