Effects of several factors were evaluated on the rate dialysis of lactic acid in a batch electrodialysis. Those factors were the concentration of source solution, temperature, current, and the circulation rate of source solution through the electrodialysis unit.
Lactate increasingly inhibited cell growth and lactic acid production in the order of Ca-lactate, $NH_4$-lactate, Na-lactate, and lactic acid. Although Ca-lactate was found to be the least inhibitory, we did not choose it since pH control using $CaCO_3$ to get Ca-lactate could cause a severe fouling of the membranes involved. Instead, we decided to use $NH_4OH$ for pH control, which resulted in the formation of $NH_4$-lactate.
The electrodialysis rate increased with the lactate concentration of the source solution. With the temperature increased from 25℃ to 35℃, the rate increased about 10%. The current was found to be the most important factor. It had strong effects on both the electrodialysis rate and the concentration difference limit between the source and the permeate solution. The effect of circulation rate of the source solution showed no clear tendency.
To test the effectiveness of in situ recovery of lactic acid from fermentation broth by electrodialysis, three cases of batch culture were carried out : pH control only, electrodialysis only, and pH control and electrodialysis. When the initial glucose concentration was 50g/L, the case with both pH control and electrodialysis was proved to be the most efficient in terms of average productivity and production yield. When the initial glucose concentration was 150g/L, the fermentation time could be remarkably shrotened by employing electrodialysis.
