Enhancement of pilot scale production of l(+)-lactic acid by fermentation coupled with separation using membrane bioreactor

Abstract

Traditional batch fermentation leads to a higher energy consumption and lower production capability because of longer culture time. In this work, a pilot scale bioreactor composed of a 3000L fermentor and external ceramic microfiltration equipment was used to perform cell-recycle fermentation. Repeat feeding medium was also used to relieve the substrate inhibition. In such pilot system, the maximum yield and productivity of l(+)-lactic acid production reached 157.22±3.42g/L and 8.77±0.15g/L/h which were 4.23% and 315.64% higher than those of batch fermentation, respectively, when equal amount of sugar was consumed. The cost of l(+)-lactic acid production was successfully reduced about two-thirds by the increase of yield and productivity. 12 rounds of cell-recycle fermentations were successfully achieved in the pilot system. The membrane filtration productivity reached to 61.27±2.74L/m2/h which increased 172.80%, while the cell damaging rate dropped to 3.88±0.18% which decreased 85.77%, compared with those of the ultrafiltration. Furthermore, the ceramic microfiltration membrane showed advantages in tolerance for the temperature, pressure and acid, compared with the organic ultrafiltration membrane. The experimental results indicated that the method could give a reference for low cost production of l(+)-lactic acid in an industrial scale.