A comprehensive study on the recovery of lactose and lactic acid from acid whey

Acid whey is a by-product of the manufacturing of concentrated yogurts and fresh cheeses, and differs from sweet whey in its higher content of lactic acid and calcium and lower pH. These characteristics negatively impact the recovery of lactose powders by hindering crystallization and causing salt precipitation. Consequently, there is an ongoing need for effective methods to remove these undesired components from acid whey. Electrodialysis and ion exchange, integrated with nanofiltration, have emerged as effective solutions. However, these methods are characterized by high complexity and the requirement of additional equipment and do not provide any valorization of lactic acid. The objective of this study is to design an alternative acid whey processing flowsheet for the recovery of all valuable components (whey proteins, lactose and lactic acid). The proposed process bears a close resemblance to the conventional processing of sweet whey, with the incorporation of a dedicated decalcification step for calcium removal. The novel aspect is the attempt to recover both lactose and lactic acid using the same nanofiltration apparatus. This thesis presents a proof of concept for lactose purification through nanofiltration, developing an integrated process combining nanofiltration in concentration mode followed by diafiltration that successfully achieves all lactose purification targets. The study also identifies the concentration factor and operating flux as key design variables for process design. Energy consumption analysis across various fluxes reveals that operating both steps at 30 L/(hm2) is the most energy efficient approach. Then, an overview of the state-of-art highlights the scarcity of studies on nanofiltration for lactic acid demineralization and thus an experimental campaign is carried out to address this gap. The experimental findings demonstrate that operating at the original pH of 4 of the lactic acid-rich permeate is inefficient, whereas raising the pH leads to a partial lactic acid purification accompanied by notable losses.