Improvement and Simulation of a Dairy Wastewater-Based Bioprocess: From Cheese Whey to Lactic Acid and Probiotic Microbial Biomass

In Mexico, cheese whey (CW) is commonly treated as a dairy wastewater despite its high lactose and nutrient content. This study evaluated cheese whey (CW) and ultrafiltered cheese whey (UF-CW) as low-cost substrates for the cultivation of the probiotic strains Lactobacillus acidophilus and Lactococcus lactis. The proposed bioprocess simultaneously enables the production of probiotic biomass and lactic acid, a high-value platform chemical with broad applications in the food, pharmaceutical, and biopolymer industries. In the first experimental trials, in which CW and UF-CW were used solely as media, fermentations lasted 36 h at 30 and 37 °C, with initial pH levels of 5 and 7. CW demonstrated a greater capacity to support the growth of lactic acid bacteria. Thus, to increase the fermentative capability of UF-CW, it was supplemented with yeast extract (YE) or corn steep liquor (CSL), and CaCO3 was added to stabilize pH, as low pH values inhibit growth and lactic acid production. The proposed strategy notably improved microbial growth in UF-CW, increasing Lc. lactis and L. acidophilus populations from 8.3 and 8.2 Log10 CFU/mL to 9.3 Log10 CFU/mL, respectively. The findings suggest that dairy wastewater can be effectively repurposed as a low-cost cultivation medium for these bacteria. ASPEN simulation analyses demonstrated that lactose conversion efficiency and final product concentration were key factors affecting process performance and economic feasibility. Among the evaluated scenarios, a 45% lactose-to-lactic acid conversion yielded the most economically favorable process performance compared with conversions of 10% and 25%. Future research should focus on enhancing fermentation yields and adopting more efficient downstream recovery techniques.