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

A process for starting-up a commercial scale, deep tank reactor for the anaerobic bioconversion of a gas substrate derived from the gasification of carbonaceous materials, the reforming of natural gas, or biogas from anaerobic digestion or comprising industrial off-gas streams and that comprises carbon monoxide, hydrogen and carbon dioxide in an aqueous menstruum containing microorganisms suitable for converting said substrate to oxygenated organic compound wherein the start-up is initiated with the menstruum containing microorganisms at an initial lower liquid height and the height of the menstruum containing microorganism is increased continuously or intermittently and the reactor has a volume of at least 25 million liters, the process comprising:

• (a) blanketing said reactor above the aqueous menstruum in a head space with at least one of carbon dioxide, nitrogen, and lower alkane to the essential exclusion of oxygen;
• (b) initially providing aqueous menstruum and microorganisms in the reactor to a depth less than about 10 meters, said aqueous menstruum being under fermentation conditions and having a concentration of said microorganisms of between about 0.03 and 3 gram per liter;
• (c) continuously supplying gas feed to a bottom portion of the reactor at a rate sufficient to increase the concentration of microorganisms, said gas feed comprising said gas substrate being supplied to a bottom portion of said reactor via at least one injector using a motive liquid to form microbubbles having a diameter of less than about 500 microns;
• and (d) increasing intermittently or continuously the volume of aqueous menstruum in said reactor to the desired capacity while increasing the concentration of microorganisms to between 3 and 500 times that in step (b), wherein by at least one of:
• (i) adjusting the gas to liquid flow ratio through an injector, (ii) changing the rate of liquid flow through an injector, and (iii) adjusting the carbon monoxide mole fraction in the gas feed by admixture with at least one other gas, the mass transfer of carbon monoxide to the aqueous menstruum in the reactor is modulated to obtain the growth of step (c) but is maintained below that amount which results in carbon monoxide inhibition.