Recovery of lactic acid from fermentation broth by electrodialysis

The overall objective of this research was to study the feasibility of utilizing electrodialysis (ED) to recover lactic acid from fermentation broths to enhance the productivity of the fermentation and reduce downstream processing costs.The electrodialysis system used was a bench-top unit, containing 20 cell pairs. Initial set-up and evaluation of performance parameters was done with a sodium chloride solution. Limiting current was a function of flow (recirculation) rate, being higher for higher flow rates. It ranged from 152 A/m$\sp2$ at 740 ml/min (corresponding to a Reynolds number of 176) to 304 A/m$\sp2$ at 1760 ml/min (Re of 419).With model lactic acid solutions, the mass of lactate transported increased linearly with time in the batch process. The flux of lactate was 328-456 g/m$\sp2$.h; flux decreased with an increase in feed concentration and with an increase of pH. However, lactate concentration in the concentrating stream was asymptotic in nature due to simultaneous water transport. Total water flux during ED was 2.79-3.83 liters/m$\sp2$.h; it decreased with an increase in feed concentration and was not affected by pH. Because of the water transport, maximum lactate concentration with the model solutions is about 125 gl$\sp{-1}$, being higher with the higher feed concentration. The minimum concentration of lactate in the diluting stream is limited by the high voltage and the corresponding high energy consumption.Higher current resulted in higher degree of separation, but at the cost of higher power and energy consumption. Efficiency decreased as the feed concentration increased. Although higher electrolyte concentration decreases the efficiency, it also reduced the electrical resistance and thus the energy consumption.With the lactic acid fermentation broth, flux was 485-526 g/m$\sp2$h for lactate, 17-20 g/m$\sp2$h for lactose, and 25-27 g/m$\sp2$h for galactose. Water flux was about 4 liters/m$\sp2$.h. Under these conditions, maximum lactate concentration achievable was 123-126 gl$\sp{-1}$. The microbial cells did not appear to significantly affect the performance of the system.Electrodialysis appears to have excellent potential in the downstream processing of lactic acid. If the electrodialysis unit is coupled to a fermentation vessel, the system can be optimized to maintain the concentration of lactate in the fermentor below its inhibitory or toxic level to the microorganism, by matching the productivity of the fermentor to the electrodialytic removal rate. This should significantly improve the overall productivity of the fermentation production of lactic acid.U of I OnlyETDs are only available to UIUC Users without author permissio