Figure 1 . Experimental setup for the continuous fermentation with clostridial cells immobilized in a fibrous bed bioreactor (FBB). Inset diagram shows the construction of the spirally wound fibrous matrices with stainless steel wire mesh as the mechanical support with gaps between adjacent layers as flow channels for liquid, gas, and solids (cells) to move freely. The highly porous fibrous matrix has a large surface area and void volume (>90% reactor volume) to allow high densities of viable cells (up to 100 g/L cell dry weight) to be immobilized by attachment to fiber surfaces and entrapment within the matrix.