4 CONCLUSION
To further increase the utilization capacity of crude glycerol and thus
make the PDO bio-production more economically feasible, a
low-butanol-producing strain C. pasteurianum C8 was subjected to
a novel automatic ALE system developed for long-term adaptation of the
strain to crude glycerol. Using a real-time monitoring of cell growth
and precise control of sufficiently low biomass, automatic ALE of the
strain with more than 100 adaptation cycles was successfully performed
within two months. Compared to the parental strain, the adapted strainC. pasteurianum G8 can tolerate up to 120 g/L crude glycerol with
a satisfactory growth rate. The PDO titer, volumetric productivity and
yield in the crude glycerol fed-batch fermentation reached 74.23 g/L,
5.30 g/L/h and 0.52 gPDO/gGly,
respectively, corresponding to the same performance as using pure
glycerol. Furthermore, the broth from a successful scale-up fermentation
(m3 scale) using the evolved strain and crude glycerol
was used to investigate a novel DSP for co-production of PDO and organic
acid esters. After biomass removal by ultrafiltration and water removal
by vacuum distillation, the dewatered broth was mixed with an acidified
alcohol for salts crystallization and removal, followed by
esterification conversion of free organic acids to their corresponding
esters. High conversion yields (97.3% for acetic acid and 92.9% for
butyric acid) were achieved using methanol as a reactant under optimized
conditions. The total recovery yield of organic acids in methyl ester
form was more than 88%. Cosmetic grade PDO without acid contamination
was easily recovered from the esterified broth via short path
evaporation with a total process yield more than 77% which could be
further improved by recycling the residuals. More pure PDO for fiber
applications can be obtained by rectification. Overall, the highly
efficient and integrated process elaborated for the first time in this
work for co-production of PDO and a variety of value-added organic acid
esters from crude glycerol without waste water represents significant
advances in developing more economic and ecological bio-manufacturing
processes for industrially appealing green chemicals.