This study aimed to develop the viable process to utilize low cost feedstock such as cassava starch to D-lactic acid by
Terrilactibacillus laevilactibacillus SK5-6 T20-20.
T. laevilacticus SK5-6 T20-20 was previously subjected to phenotypic adaption so that it could grow and produce D-lactic acid from the medium with lowered yeast extract. In addition, recovery of D-lactic acid from the fermentation broth using the surface-modified coconut shell activated carbon was also performed. The preliminary results from the laboratory scale were collected for further process design in the pilot scale test. Fermentation platform validation for D-lactic acid production by
T. laevilacticus SK5-6 T20-20 was successfully conducted in 5 L, 30 L, and 300 L fermentors. The final concentration and yield were met the targeted production performance. From the fermentation results in a 5 L fermenter, D-lactic acid concentration was 90.58 g/L with the corresponding yield of 0.73 g/g glucose and productivity of 1.89 g/L×h. Considering D-lactic acid production in 30 L and 300 L fermentors, the results revealed that the final D-lactic acid titer were 84.64 g/L and 78.31 g/L with the corresponding yield of 0.77 g/g glucose and 0.70 g/g glucose and the productivity of 1.14 g/L×h and 1.22 g/L×h, respectively. Fermentation process scale-up in 3000 L was conducted to confirm the platform repeatability and reproducibility in the shake flask toward the 300 L fermentor. The average final D-lactic acid titer of 86.45 g/L with 0.82 g/g yield and 1.27 g/L×h productivity was acquired.
To separate and purify lactic acid from the fermentation broth, activated carbon from coconut shells was used to adsorb metal ions remained in the fermentation broth. It was observed that coconut shell activated carbon (CSAC) grafted with carboxymethyl cellulose (2%) and citric acid (2%) could adsorb anions remained in the fermentation broth. Ion removal process began with loading 10 L broth into 1 kg CSAC without prior pH adjustment. The adsorption took 2.5 h at room temperature for metal ion removal. Later, the broth was loaded into the grafted CSAC at the same loading ratio. The adsorption occurred under the same operating conditions. After 2-step adsorption, lactic acid was recovered with the purity percentage of 81.70 and the recovery percentage of 98.93. Most of metal ions, anions, and glucose were found to be adsorbed on the CSAC surface with the low loss of lactic acid.
