Abstract:
Brackish water reverse osmosis (BWRO) and seawater reverse osmosis (SWRO) membranes were used in a two-stage reverse osmosis (RO) unit to recover, pre-purify, and pre-concentrate lactic acid. Calcium lactate, sodium lactate, and ammonium lactate were used as model feed solutions. The operating pressure showed a pronounced effect on lactate passage through the first BWRO unit, and the Donnan exclusion effect and hydrogen bonding were responsible for cation rejection. Calcium ions were rejected at the BWRO unit because of low diffusion rate and charge interaction at the surface. However, monovalent ions formed hydrogen bonds with the carbonyl group of the membrane that allowed passage across the membrane. The second SWRO unit was for pre-concentrating lactic acid. A high lactate purity of 99.2% with a total recovery of 50.5% was acquired from calcium lactate feed solution. Lower purity with higher lactate recovery was obtained when the feed solution was sodium lactate and ammonium lactate. When the actual fermentation broth was used in the two-stage RO unit, a slightly lower recovery and purity of lactic acid were obtained. It was claimed that the total ions present in the fermentation broth were responsible for the low efficiency of the two-stage RO unit.
