Strategies for maximizing removal of lactic acid from acid whey - Addressing the un-processability issue

Maximum removal of lactic acid (LA) from acid whey (AW) is essential for further processing of the AW waste stream. Hence, one and two step nanofiltration (NF) and nano diafiltration (NDF) approaches were applied to evaluate the removal efficiency of LA from AW at low and high pH, respectively. NDF at pH 3.0 achieved removal of ∼50-55% LA with a diafiltration factor (DF) of 4. Addition of diafiltration water with adjusted pH to prevent the pH fluctuations with dilutions had no significant impact on the extent of LA permeation. Adjusting pH of AW to pH 7.3 or 10.5 resulted in formation of precipitates which were removed by centrifugation, bringing about ∼22% removal of LA. The resultant supernatants were further subjected to NDF giving an overall LA removal of ∼51-55%. Additional removal of LA appeared hindered due to strong complexation of LA with lactose. This complex remained with the retentate due to the rise in molecular weight. Using a stepwise pH adjustment, first to obtain a supernatant at pH 10.5 followed by pH readjustment to 3.0 and then NF, it was possible to achieve an overall LA removal of ∼66%. Stepwise pH adjustment during NF of AW appears to be a feasible way to remove substantial amounts of LA to allow for downstream processing.