Finally, fermenters are geometrically designed as packed-bed fermenters, bubble-column type, air-lift fermenter, and tank fermenters (Figs. 5–8). The fed-batch, chemostat, and membrane cell recycle systems were specially studied to overcome growth inhibition of low organic substrates concentrations ( Chen, 1996 ; Hochfeld, 2006 ; Liu, Sun, & Chen, 2014 ).