OPTIMIZATION OF L-(-LACTIC ACID PRODUCTION BY RING AND DISC PLASTIC COMPOSITE SUPPORTS THROUGH REPEATED-BATCH BIOFILM FERMENTATION())

Four customized bioreactors, three with plastic composite supports (PC S) and one,vith suspended cells (control), were operated as repeated-b atch fermenters for 66 days at pH 5 and 37 degrees C, The working volu me of each customized reactor was 600 ml, and each reactor's medium wa s changed every 2 to 5 days for 17 batches, The performance of PCS bio reactors in long-term biofilm repeated-batch fermentation was compared with that of suspended-cell bioreactors in this research, PCS could s timulate biofilm formation, supply nutrients to attached and free susp ended cells, and reduce medium channelling for lactic acid production, Compared with conventional repeated-hatch fermentation, PCS bioreacto rs shortened the lag time by threefold (control, 11 h; PCS, 3.5 h) and sixfold (control, 9 h; PCS, 1.5 h) at yeast extract concentrations of 0.4 and 0.8% (wt/vol), respectively, They also increased the lactic a cid productivity of Lactobacillus casei subsp. rhamnosus (ATCC 11443) by 40 to 70% and shortened the total fermentation time by 28 to 61% at all yeast extract concentrations, The fastest productivity of the PCS bioreactors (4.26 g/liter/h) was at a starting glucose concentration of 10% (wt/vol), whereas that of the control (2.78 g/liter/h) was at 8 % (wt/vol), PCS biofilm lactic acid fermentation can drastically impro ve the fermentation rate with reduced complex-nutrient addition.