Effect of some operating variables on citrate recovery from model solutions by electrodialysis
The effect of pH and temperature (straight theta) on the overall performance indicators (i.e., solute recovery, rho, and Faraday, eta, efficiencies; specific energy consumption, epsilon, solute, JS, and water, JW, fluxes) of batch electrodialytic recovery of citric acid from model solutions was assessed at different values of feed solute concentration (cSf) and electric current density (j). Regardless of the initial feed concentration used, rho and JS were found to be independent of straight theta; eta and JW exhibited a positive trend with respect to straight theta, while epsilon a negative one. At the maximum temperature tested (33 degrees C), as the pH of the feed solution was varied from 3 to 7, rho increased from 0.90 +/- 0.08 to 0.97 +/- 0.02, eta grew from 0.09 +/- 0.02 to 0.50 +/- 0.01, JS practically doubled, epsilon reduced about 8 times, but JW increased from 3 to 4 times. So, the optimal conditions for this technique are to be determined by balancing the savings in the investment and maintenance costs against the energy costs. Copyright John Wiley & Sons, Inc.
Electrodialysis of model lactic acid solutions
Abstract Electrodialysis of model lactic acid solutions at various concentrations, pH values and modes of operation was evaluated in a bench-top system with 20 cell pairs. The limiting current (determined with 6 g liter −1 NaCl) ranged from 152 A m −2 at a Reynolds number (Re) of 176 to 304 A m −2 at Re = 419. In the batch recycle mode, the mass of lactate transported increased linearly with time. The flux of lactate was 328–456 g m −2 h −1 ; flux decreased with an increase in feed concentration and with an increase of pH. Water flux during ED was 2·79-3·83 liters m −2 h −1 ; it decreased with an increase in feed concentration and was not affected by pH. This water transport limits the maximum lactate concentration in the concentrating stream to 135 g liter −1 with feed concentrations of 45–95 g liter −1 . Coulomb efficiencies with NaCl and lactate solutions in batch, single-pass and feed-and-bleed modes were 0·55-0·8.
Downstream processing of lactic acid-whey permeate fermentation broths by hollow fiber ultrafiltration
ConclusionsMembrane filtration is a suitable method for cell harvesting and clarification of fermentation broths. Hollow fiber ultrafilters gave essentially 100% rejection ofL. bulgaricus cells from a whey permeate fermentation broth. A combination of low pressures and high velocity generally gave the best permeate flux. Fermentation media components (in this case, from the whey permeate) contributed significantly to fouling. Considering the pressure limitations of the current generation of asymmetric hollow fiber modules and the changes in physical properties of the fermentation broths, a cell concentration of 100–150 g/L could be obtained with the flux still relatively high (above 20LMH), although the chemical compatibility of the membrane module itself under long-term exposure to high acid conditions should be considered.