The possibility of creating a biorefinery using inexpensive biomass has attracted a great deal of attention, which is mainly focused on the improvement of strains and fermentation, whereas few resources have been spent on downstream processing. Bio‐based chemical downstream processing can become a bottleneck in industrial production because so many impurities are introduced into the fermentation broth. This review introduces a technique referred to as salting‐out extraction, which is based on the partition difference between chemicals in two phases consisting of salts and polymers or hydrophilic solvents, hydrophobic solvents, and amphipathic chemicals. The effects of solvents and salts on the formation of two phases were discussed, as was the use of this method to recover bio‐based chemicals. This review focused on the separation of hydrophilic chemicals (1,3‐propanediol, 2,3‐butanediol, acetoin, and lactic acid) from fermentation broths. Diols could be recovered at a high yield from fermentation broths without pretreatment especially with a hydrophilic solvent‐based system, whereas the recovery of organic acids was slightly lower. Most of the impurities (cells and proteins) were removed during the same step. Extractive fermentations were also used for polymer‐based aqueous two‐phase systems.

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1,3-Propanediol (1,3-PD) can be produced from glycerol by Klebsiella pneumoniae under micro-aerobic conditions. Recently, this fed-batch fermentation process has been successfully scaled up to 1 m(3). The final 1,3-PD concentration, molar yield and volumetric productivity of 72 g l(-1), 57% and 2.1 g l(-1 )h(-1), respectively, are close to those of 75 g l(-1), 61%, and 2.2 g l(-1 )h(-1) under anaerobic conditions. This process would be suitable for the production of 1,3-PD on a large scale.

Crude glycerol is an ideal feedstock for bioproduction of 1,3-propanediol (1,3-PDO) while pure culture always shows low substrate tolerance and limited productivity. In this study, an anaerobic microbial consortium for conversion of crude glycerol was selected and its 1,3-PDO production capacity was evaluated. The consortium was obtained from anaerobic activated sludge by 19 serial transfers and mainly consisted of 94.64% Clostridiaceae and 4.47% Peptostreptococcaceae. The consortium adapted well with high glycerol concentration of 120 g/L as well as wide substrate concentration fluctuation from 15 to 80 g/L, producing 60.61 and 82.66 g/L 1,3-PDO in the batch and fed-batch fermentation, with the productivity of 3.79 and 3.06 g/(L∙h), respectively, which are among the best results published so far. Furthermore, mini consortia isolated by serial dilution exhibited similar microbial composition but gradually decreasing tolerance to crude glycerol. Four randomly selected Clostridium butyricum displayed different substrate tolerance and insufficient 1,3-PDO production capacity. This work demonstrated that the high adaptation to crude glycerol of the consortium was the collaborative effort of different individuals.

Microbial consortium is an alternative for bioconversion of crude glycerol to value-added products whereas concerns about the process stability in long-term operation existed. The aim of this study is to evaluate the feasibility of using an anaerobic microbial consortium as inoculum for continuous conversion of crude glycerol to 1,3-propanediol (1,3-PDO). Performances of continuous fermentations with the consortium inoculum were evaluated under different dilution rates and glycerol feed concentrations. The highest 1,3-PDO production of 57.86 g/L was achieved with a productivity of 5.55 g/(L·h). Analyses of kinetic data showed that the consortium maintained a consistent pattern for 1,3-PDO production under different operating conditions despite changes in community composition. The continuous fermentation by the consortium was able to operate for a longer period of time (31 volume changes) than that using pure culture (24 volume changes) with the average 1,3-PDO concentration of 53.52 g/L and productivity of 6.69 g/(L·h) under glycerol-excess condition, which could be contributed to the intraspecies diversity among Clostridium butyricum in the consortium. Under glycerol-limited conditions, however, a spontaneous oscillation of the consortium was observed after continuous operation for about 120 h, along with severe fluctuations of the microbial community. The oscillatory behavior could be reduced by increasing the dilution rates and was likely the metabolic feature of C. butyricum.