Integrated Membrane Process for the Purification of Lactic Acid from a Fermentation Broth Neutralized with Sodium Hydroxide

Lactic acid, mainly produced by fermentation, has been widely used in the food, chemical, and pharmaceutical fields. Because of the high downstream processing costs in traditional technology, the cost-effective production of high-purity lactic acid has remained a challenge for decades. This study provides an integrated membrane process to recover lactic acid from sodium salt fermentation broth that consists of ceramic membrane filtration, nanofiltration (NF), and bipolar membrane electrodialysis (BMED). In the ceramic membrane process, the flux changed with the membrane pore size in the order of 50 nm > 200 nm > 500 nm > 20 nm. At an operating pressure of 0.1 MPa, the flux of the membrane with a pore size of 50 nm reached a maximum of 192 L.m(-2).h(-1), and the removal rate of cells was up to 99.3%. In the subsequent NF step, the flux increased linearly with the operating pressure from 0.5 to 2.0 MPa, whereas the rejection rates of Mg2+, Ca2+, and Na+ increased with increasing TMP, and a flux of 5.0 L.m(-2).h(-1) was obtained at the operating pressure of 2.0 MPa, with 87.7% of Ca2+, 95.0% of Mg2+, and 98.9% of protein being retained. The BMED process was developed for the conversion of 95.0% NaL into NaOH and HL, and the energy consumption was 1.05 kWh.kg(-1) under a current density of 400 A.m(-2). Our results indicate that the proposed integrated membrane process is technically feasible for lactic acid production from fermentation broth.