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.