Abstract: A process of general applicability in the microbiological field wherein a culture is subjected to periods of availability and non-availability of an essential energy source such as a carbon source, i.e. the energy source is supplied in pulses. The efficiency of the culture in converting substrate carbon to cellular carbon varies depending upon the relative duration of the periods of availability and non-availability of the energy source. Thus depending upon the relative duration chosen the process can be applied differently, i.e. when the efficiency is high the process is suitable for single cell protein production while when it is low it is suitable for waste water treatment.

Abstract: An energy recovery system for use in conjunction with a fermenter operating with an overpressure preferably of 5 to 10 bars gauge. Gas under pressure leaving the fermenter passes to a gas expander and the power produced by the expander is used to drive the compressor which supplies gas under pressure to the fermenter. The combination of the energy recovery system with a fermenter provides an efficient means for operating a process for the production of single cell protein.

Abstract: A method and apparatus for continuously circulating a mixture comprising a liquid and a gas around a system comprising a riser and a downcomer and a gas disengagement section in which liquid flows downwardly at a velocity which does not exceed 0.2 meters per second and is being injected into a lower section of the riser. The method and apparatus are particularly useful for conducting aerobic fermentations.