Identifying conditions to optimize lactic acid production from food waste

There is an increased demand for lactic acid for the production of biopolymers and to aid nutrient removal in wastewater treatment. Food waste offers a source of soluble sugars to produce lactic acid, which does not increase land demand, but digestion conditions have yet to be optimized when co-digested with primary sludge. Food waste was collected from cafeteria waste bins, homogenized and seeded with primary sludge. A Box Behnken Response surface design was used to optimize lactic acid production based on pH, temperature, loading rate, and retention time. Subsequent experiments verified and refined those conditions 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. Digestion rates of carbohydrates to lactic acid demonstrate homolactic fermentation as the dominant microbial pathway. Approximately 60% of the lactic acid produced was L(+) lactic acid. The ratio of soluble chemical oxygen demand to NH4-N was 176 indicating high potential for biological nutrient removal