The present state of fermentation reactors

The actual application of fermenters other than stirred tanks in industry is scarce. Only minor changes have been performed in stirred‐tank design. Due to the increase of energy costs even the trend to higher power‐input rates has been stopped. Progress has been high as far as automatic analysis and control are concerned. For single‐cell protein plants bubble column and air‐lift loop systems have been improved. Surface aeration has regained interest because its energy cost can be kept considerably lower than with submerged systems. In the meantime the experience gathered with deep‐tank fermentation has begun to exert influence even on sewage treatment plants. A number of examples demonstrate that better economy has been achieved when flat basins are replaced by reactors of considerable depth.