A novel membrane-integrated fermentation reactor system: application to pyruvic acid production in continuous culture by Torulopsis glabrata

Abstract

This paper describes the performance of a novel bio-reactor system, the membrane-integrated fermentation reactor (MFR), for efficient continuous fermentation. The MFR, equipped with an autoclavable polyvinylidene difluoride membrane, has normally been used for biological wastewater treatment. The productivity of the MFR system, applied to the continuous production of pyruvic acid by the yeast Torulopsis glabrata, was remarkably high. The volumetric productivity of pyruvic acid increased up to 4.2 g/l/h, about four times higher than that of batch fermentation. Moreover, the membrane was able to filter fermentation broth for more than 300 h without fouling even though the cell density of the fermentation broth reached 600 as OD(660). Transmembrane pressure, used as an indicator of membrane fouling, remained below 5 kPa throughout the continuous fermentation. These results clearly indicate that the MFR system is a simple and highly efficient system that is applicable to the fermentative production of a range of biochemicals.

Membrane-Integrated Fermentation System for Improving the Optical Purity ofD-Lactic Acid Produced during Continuous Fermentation

“…Critical flux measurements were conducted according to the stepwise flux method, using the MFR system previously reported. 3) The batch cultivation broth (1.5 L) was poured into the MFR system and filtered. The permeate was returned to the fermentor, and the permeate flux increased stepwise every 15 min while monitoring the transmembrane pressure (TMP).…”

“…3) The concept of critical flux was applied to the MFR system as an operational strategy to reduce the decline in flux caused by membrane fouling, thereby facilitating long-term fermentation. The critical operating flux for the cultivated broth was thus determined for each of the 3 strains: the respective critical flux levels for S. inulinus, S. laevolacticus, and S. terrae Continuous D-lactic acid fermentation with the 3 strains was carried out for 280-296 h at the dilution rate just given for each strain after 24 h of batch fermentation.…”

“…1,2) Although continuous fermentation presents such difficulties as membrane fouling and contamination, we have recently developed a membraneintegrated fermentation reactor (MFR) fitted with a membrane normally used for biological wastewater treatment which enabled continuous fermentation without membrane fouling or contamination. 3) Lactic acid is a fermentation product that has recently been utilized as a raw material for producing poly(lactic acid) (PLA), a renewable and biodegradable plastic. 4) PLA can occur as poly(L-lactic acid) (PLLA), poly(Dlactic acid) (PDLA), or poly(DL-lactic acid) (PDLLA), these being respective polymers of L-lactic acid, D-lactic acid, and DL-lactic acid.…”

A Membrane-Integrated Fermentation Reactor System: Its Effects in Reducing the Amount of Sub-Raw Materials forD-Lactic Acid Continuous Fermentation bySporolactobacillus laevolacticus

“…The filtration condition was set at a flux below the critical flux of individual bacteria, and intermittent filtration was performed, in which filtration was stopped for 1-min intervals over 9 min. The critical flux of the S. laevolacticus batch cultivated broth determined according to the satepwise flux method, 5) was 0.600 m 3 /m 2 /d. Thus the filtration conditions comprised constant dilution rates: 0.17 h À1 and flux, 0.530 m 3 /m 2 /d.…”

“…5) Continuous fermentation was performed essentially according to the batch fermentation conditions described above. However, because the saturated solubility of D-lactic acid calcium was 70 g/L (data not shown), we used 80 g/L of raw cane sugar and 8 N of calcium hydroxide.…”