ELECTRODIALYSIS OF MODEL LACTIC-ACID SOLUTIONS

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.