The present invention provides a bioreactor comprising a vessel having a
bottom region and an interior configured to contain an aqueous suspension
of biomass and media. A first gas outlet is provided at the bottom region
of the vessel. The first gas outlet is positioned to introduce a first
stream of gas to promote growth of the biomass on the media. A lift tube
is disposed within the vessel, the lift tube having an inlet disposed at
the bottom region of the vessel. A second gas outlet is disposed proximal
the lift tube inlet to feed gas to the inlet of the lift tube.
