Fermentation process for improved oxygen utilization

A process for the production and separation of single cell protein employing fermentation apparatus means for improved oxygen utilization in the continuous aqueous aerobic fermentation of a microorganism, comprising a fermentation section with an upper contiguous absorber section communicating therewith for the passage of gaseous effluent from the upper area of said fermentation section into the lower portion of said absorber section, and for the passage of liquids from the absorber section into said fermentation section,

• wherein said fermentation section contains liquid aqueous ferment and comprises means for receiving a molecular oxygen-containing gas, said molecular oxygen gas-receiving means positioned in the lower portion of said fermentation section below the normal liquid level of said aqueous liquid ferment, and means for receiving a carbon energy source material and a nitrogen source material,
• wherein said absorber section comprises, in sequence relative to said fermentation section, a foam-breaking zone, a gas-contacting zone, a liquid knock-out zone of substantially expanded diameter relative to said gas-contacting zone and sufficient to substantially reduce the linear gas velocity of gases exiting said gas-contacting zone, gas-venting means at the upper area of said knock-out zone,
• which process comrises the steps of
• (a) fermenting under aqeuous fermentation conditions in said fermentation section at least one water-soluble oxygenated hydrocarbon compound as carbon energy substrate with at least one oxygenated hydrocarbon metabolizing microorganism under aqueous fermentation conditions, employing molecular oxygen, assimilable nitrogen-source and aqueous nutrient medium,
• (b) withdrawing aqueous ferment rich in cellular material from said fermentation section,
• (c) separating cellular material from said rich aqueous ferment, leaving lean fermentation liquid,
• (d) cooling said lean fermentation liquid,
• (e) recycling said cooled lean fermentation liquid to said gas-contacting zone
• (f) feeding make-up water and nutrients other than oxygenated hydrocarbon compounds to said gas-contacting zone,
• (g) passing molecular oxygen-containing gases into the lower portion of said fermentation section below the liquid level of said aqueous ferment and upwardly through said aqueous ferment,
• (h) discharging now-partially oxygen-depleted molecular oxygen-containing gases from said fermentation section into said foam-breaking zone of said contiguous absorber section, and passing said partially oxygen-depleted gases into said gas-contacting zone
• (i) contacting in counter-current contact in said gas-contacting zone said partially depleted molecular-oxygen-containing gases with said make-up water and nutrients and said cooled lean fermentation liquor, thereby further utilizing the oxygen content of said partially depleted molecular oxygen-containing gases, and forming an oxygen-augmented mixed make-up liquid,
• (j) discharging remaining exhaust gases,
• (k) passing the oxygen-augmented mixed make-up liquid downwardly, through said foam-breaking zone of said absorber section into said fermentation section, and
• (l) recovering said separted cellular material as a single cell protein product.