Anaerobic microbial conversion of substrate to metabolite

In the microbial conversion of a substrate to a metabolite under anaerobic conditions in a fermenter, (a) the fermenter is a bubble-tube reactor with no mechanically moving inserts, and (b) a gas free from O2 is pressed into the lower region of the reactor during the fermentation to convey the fermentation feed. O2-free gases are the fermentation gases taken off at the head of the reactor, and/or inert gases, e.g. N2, CO2 or Ar. Rate of gas feed is 0.001-0.2 (0.03-0.07) vvm, fed centrally (pref. axially) to the bottom of the tower reactor through a pipe or a gasification ring. Reactor pref. has a ratio of height:dia. of 5:20-10, and may have static inserts promoting mixing, esp. recycling loops, which are central or on the walls and act as sepn. wall. Prods. and/or recycled culture medium is sprayed onto the foam, through a nozzle in the upper part of the reactor, to control foam. Microorganism is pref. Clostridium butyricum. The aim is to improve the conduct of a process for the microbial conversion of a substrate to form a metabolite in anaerobic conditions. To do so, a tower-like pneumatic reactor without any mechanically actuated components is used as the fermenter and gas bubbles are generated to start the process during fermentation by forcing an oxygen-free gas in the lower region of the reactor.