Processes for starting up and operating anaerobic, deep tank fermentation systems to anaerobically bioconvert hydrogen and carbon monoxide in a gaseous substrate stream to oxygenated organic compounds and for steady operation of such fermentation systems are shown. Injectors use a motive liquid to introduce gas substrate as a stable gas-in liquid dispersion into the deep tank fermentation reactor where 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,wherein the mass transfer of carbon monoxide to an aqueous menstruum in the reactor is controlled to obtain the robust growth of the microorganism and/or continued conversion of gas substrate while maintaining the carbon monoxide concentration below that amount which is unduly adverse to the microorganism.