Processes for starting up and operating deep tank anaerobic fermentation reactors for making oxygenated organic compound from carbon monoxide and hydrogen

A process for the anaerobic bioconversion of a gas substrate comprising carbon monoxide, hydrogen and carbon dioxide in a deep tank bio-reactor by contact of the gas substrate with an aqueous menstruum containing microorganisms suitable for converting said gas substrate to an oxygenated organic compound in a bubble column bioreactor having a liquid capacity of at least 1 million liters, the process further comprising:

• (a) blanketing said reactor above the aqueous menstruum in a head space with a head space gas comprising at least one of carbon monoxide, hydrogen, carbon dioxide, nitrogen, and a lower alkane to the essential exclusion of oxygen;
• (b) continuously supplying a feed gas comprising at least a portion of the gas substrate to a bottom portion of said reactor at a rate sufficient to maintain a predetermined concentration of microorganisms in the aqueous menstruum:
• (c) injecting the gas substrate and a recycled portion of the aqueous menstruum by the use of a plurality of feed gas-liquid injectors in the form of slot injectors to inject said feed gas into the bottom portion of said bio-reactor using the recycled aqueous menstruum as a motive liquid to form a dispersion of liquid and microbubbles having a diameter of less than about 500 microns created by dispersion of the feed gas;
• (d) injecting the dispersion directly from the injectors into the aqueous menstruum contained in the bioreactor;
• and,
• (e) operating in a liquid retention mode that maintains sufficient height of the aqueous menstruum in the bioreactor such that the process converts at least 80% of the carbon monoxide and the hydrogen to an oxygenated organic compound wherein:
• the mass transfer of carbon monoxide to the aqueous menstruum in the bioreactor is modulated to maintain the microorganisms at the predetermined concentration of step (b) and the carbon monoxide concentration below that amount which results in carbon monoxide inhibition by at least one of:
• (i) adjusting the gas to liquid flow ratio through an inject,
• (ii) changing the rate of liquid flow through an injector, and
• (iii) adjusting the carbon monoxide mole fraction in the feed gas by admixture of the gas substrate with at least one other gas to maintain a stable operation of the gas-in liquid dispersion.