A system for producing a protein-rich nutrient supplement from a fermentation process using anaerobic bacteria, comprising: a fermentation vessel connected to a gas inlet line configured for flowing a gaseous substrate into the fermentation vessel and a liquid inlet line configured for supplying a culture medium into the fermentation vessel containing the anaerobic bacteria to ferment the gaseous substrate and the culture medium into a fermentation liquid broth which contains fermentation products which include at least one oxygenated hydrocarbonaceous compound; a first cell separator connected to one or more first outlet lines of the fermentation vessel and configured to receive a first flow of the fermentation liquid broth from the fermentation vessel and to separate the first flow of the fermentation liquid broth into a first cell-containing suspension and a first cell-free permeate solution which contains mainly the fermentation products generated by the fermentation process and is ready for further processing by distillation and other processes; a processing chamber connected to one or more second outlet lines of the first cell separator and configured to receive the first cell-free permeate solution from the first cell separator and to process the first cell-free permeate solution into an oxygenated hydrocarbonaceous compound; one or more cell rupturing devices connected to the first cell separator and configured to receive the first cell-containing suspension, and to rupture cell membranes of the first cell-containing suspension to generate a homogenate; one or more fractionators connected to one or more third outlet lines of the one or more cell rupturing devices and configured to receive the homogenate from the one or more cell rupturing devices and to fractionate the homogenate into a first protein-containing portion and a protein-containing cell debris portion; a second cell separator connected to one or more fourth outlet lines of the fermentation vessel and configured to receive a second flow of the fermentation liquid broth from the fermentation vessel and to separate the second flow of the fermentation liquid broth into a second cell-containing suspension and a second cell-free permeate solution, and further configured such that a first amount of the second cell-free permeate solution is delivered to the processing chamber and that an amount of the second cell-containing suspension, containing anaerobic bacteria cells, is delivered back to the fermentation vessel via an outlet line to therein undergo further fermentation. a fermentation vessel connected to a gas inlet line configured for flowing a gaseous substrate into the fermentation vessel and a liquid inlet line configured for supplying a culture medium into the fermentation vessel containing the anaerobic bacteria to ferment the gaseous substrate and the culture medium into a fermentation liquid broth which contains fermentation products which include at least one oxygenated hydrocarbonaceous compound; a first cell separator connected to one or more first outlet lines of the fermentation vessel and configured to receive a first flow of the fermentation liquid broth from the fermentation vessel and to separate the first flow of the fermentation liquid broth into a first cell-containing suspension and a first cell-free permeate solution which contains mainly the fermentation products generated by the fermentation process and is ready for further processing by distillation and other processes; a processing chamber connected to one or more second outlet lines of the first cell separator and configured to receive the first cell-free permeate solution from the first cell separator and to process the first cell-free permeate solution into an oxygenated hydrocarbonaceous compound; one or more cell rupturing devices connected to the first cell separator and configured to receive the first cell-containing suspension, and to rupture cell membranes of the first cell-containing suspension to generate a homogenate; one or more fractionators connected to one or more third outlet lines of the one or more cell rupturing devices and configured to receive the homogenate from the one or more cell rupturing devices and to fractionate the homogenate into a first protein-containing portion and a protein-containing cell debris portion; a second cell separator connected to one or more fourth outlet lines of the fermentation vessel and configured to receive a second flow of the fermentation liquid broth from the fermentation vessel and to separate the second flow of the fermentation liquid broth into a second cell-containing suspension and a second cell-free permeate solution, and further configured such that a first amount of the second cell-free permeate solution is delivered to the processing chamber and that an amount of the second cell-containing suspension, containing anaerobic bacteria cells, is delivered back to the fermentation vessel via an outlet line to therein undergo further fermentation.