Fig. 2.

Overview on the most advantageous fermentation methods and configurations for continuous solvent production with solventogenic and acetogenic clostridia. a Multi-stage process with two chemostat stages; high cell density cultivation in a b continuous cell retention system and with c–f immobilized systems and biofilm reactors: c chemostat with free-flowing immobilized cell particles, d packed-bed reactor (PBR), e trickle bed reactor (TBR), f hollow fiber membrane reactor (HFMBR). TBR (e) and HFMBR (f) are mainly used for gas fermentation. Integrated product recovery methods: g in-line recovery and h in situ recovery. (Modified from [82, 267, 275, 314, 341]