Separation of lactic acid from fermented residual resources using membrane technology

Lactic acid can be derived from microbial fermentation and be used as a platform chemical in various industrial applications. This study aims to investigate the challenges involved in combining a low-cost, heterogeneous feedstock, such as a mixture of candy-waste and digestate, with an optimized downstream strategy to achieve maximum recovery of high-purity lactic acid, targeting low energy consumption. To achieve this goal, four membrane separation technologies, namely microfiltration, nanofiltration, monopolar, and bipolar electrodialysis, were combined to design two purification processes. Microfiltration served as the pre-purification step, followed by either process A, which combined nanofiltration and bipolar electrodialysis, or process B, a combination of monopolar and bipolar electrodialysis. The findings emphasized the importance of pH as a control factor. Nanofiltration at pH 2.8 and monopolar electrodialysis at pH 4.0 led to increased lactic acid recovery. Moreover, it was observed that process B resulted in 1.09-fold higher lactic acid recovery than process A. However, process A had a 1.19-fold lower specific energy consumption, and the presence of ions in the final solution was reduced by 5-fold. In both processes lactic acid was separated from sugars and organic acids. Overall, the findings of this study suggest that membrane separation technology is a viable method for separating lactic acid produced from a mixture of residual candy-waste and digestate.