Identifying conditions to optimize lactic acid production from food waste

There is an increase in the demand for lactic acid for the production of biopolymers. Food waste offers a steady source of soluble sugars to produce lactic acid that does not increase land use, but the optimal digestion conditions for co-digestion with sludge had yet to be studied. In this study, waste collected from cafeteria refuse bins was seeded with primary sludge to study the optimal conditions for lactic acid production. Response surface methodology was used to optimize lactic acid production based on pH, temperature, loading rate, and retention time. The resulting optimum was verified and refined to optimize for both yield and concentration of lactic acid. When optimized for concentration and yield, 58 g L-1 and 48 g L-1 lactic acid were achieved respectively and retention time was reduced three-fold over previous experiments which did not use sludge as a co-digestant. Digestion of carbohydrates indicates homolactic fermentation is the dominating microbial pathway and 97% of the theoretical yield achieved. Optical purity of the resulting lactic acid was found to be 60% L form, which can be concentrated and mixed for bioplastic fabrication.