An apparatus for producing hydrogen and methane from organic waste, comprising: a) a biohydrogenator including a completely mixed bioreactor having an input for receiving organic waste into said completely mixed bioreactor and a gravity settler located downstream of said completely mixed bioreactor and hydraulically connected with an output of said completely mixed bioreactor for receiving an output from said completely mixed bioreactor, including a feedback conduit connecting a bottom of the gravity settler to the completely mixed bioreactor for recirculating settled biomass from said gravity settler to said completely mixed bioreactor, and including an output conduit from the bottom of said gravity settler for discharging of excess biomass, wherein the gravity settler is decoupling SRT (Solids Residence Time) from HRT (Hydraulic Retention Time); b) hydrogen producing microorganisms located in said completely mixed bioreactor; c) a biomethanator located downstream of said gravity settler and hydraulically connected with an output of said gravity settler; and d) wherein the organic waste entering the completely stirred bioreactor is broken down microbiologically by said hydrogen producing microorganisms to predominantly hydrogen gas and carbon dioxide, and a mixture of volatile fatty acids and primary alcohols, and wherein hydrogen gas and carbon dioxide are emitted from the completely mixed bioreactor, and wherein a liquid effluent containing the volatile fatty acids, primary alcohols and hydrogen producing microorganisms flow to the gravity settler and when in the gravity settler the hydrogen producing microorganisms settle to the bottom of the gravity settler and are concentrated in the gravity settler while liquid effluent containing predominantly the volatile fatty acids and the primary alcohols flow into the biomethanator wherein the volatile fatty acids and the primary alcohols are broken down microbiologically predominantly to methane gas and carbon dioxide, and wherein settled hydrogen producing microorganisms in the bottom of the gravity settler are recirculated back to the completely mixed bioreactor, and wherein the methane gas and carbon dioxide produced in the biomethanator are emitted and liquid waste containing residual organics are discharged from said biomethanator. a) a biohydrogenator including a completely mixed bioreactor having an input for receiving organic waste into said completely mixed bioreactor and a gravity settler located downstream of said completely mixed bioreactor and hydraulically connected with an output of said completely mixed bioreactor for receiving an output from said completely mixed bioreactor, including a feedback conduit connecting a bottom of the gravity settler to the completely mixed bioreactor for recirculating settled biomass from said gravity settler to said completely mixed bioreactor, and including an output conduit from the bottom of said gravity settler for discharging of excess biomass, wherein the gravity settler is decoupling SRT (Solids Residence Time) from HRT (Hydraulic Retention Time); b) hydrogen producing microorganisms located in said completely mixed bioreactor; c) a biomethanator located downstream of said gravity settler and hydraulically connected with an output of said gravity settler; and d) wherein the organic waste entering the completely stirred bioreactor is broken down microbiologically by said hydrogen producing microorganisms to predominantly hydrogen gas and carbon dioxide, and a mixture of volatile fatty acids and primary alcohols, and wherein hydrogen gas and carbon dioxide are emitted from the completely mixed bioreactor, and wherein a liquid effluent containing the volatile fatty acids, primary alcohols and hydrogen producing microorganisms flow to the gravity settler and when in the gravity settler the hydrogen producing microorganisms settle to the bottom of the gravity settler and are concentrated in the gravity settler while liquid effluent containing predominantly the volatile fatty acids and the primary alcohols flow into the biomethanator wherein the volatile fatty acids and the primary alcohols are broken down microbiologically predominantly to methane gas and carbon dioxide, and wherein settled hydrogen producing microorganisms in the bottom of the gravity settler are recirculated back to the completely mixed bioreactor, and wherein the methane gas and carbon dioxide produced in the biomethanator are emitted and liquid waste containing residual organics are discharged from said biomethanator.