Municipal biopulp as substrate for lactic acid production focusing on downstream processing

Abstract

A primary target in lactic acid production is to reduce the production cost. Due to its high content of fermentable carbohydrates and low-cost, municipal biopulp can represent a promising feedstock to match this target. In addition to low-cost raw materials, a cost-effective downstream separation process (DSP) for the recovery of lactic acid is necessary to improve the overall competitiveness of the process. In the present study, lactic acid was produced from municipal biopulp obtaining a yield and titer of 82.6 ± 2.3%. g/g of total sugars and 16.1 ± 0.4 g/L, respectively. Two downstream processes (DSP1 and DSP2) were also investigated to recover lactic acid from the fermentation broth. DSP1 consisted of a pre-purification step (centrifugation, ultrafiltration, and activated carbon) followed by ion-exchange and vacuum distillation. DSP1 resulted in a recovery of 75.70 ± 1.5% and lactic acid purity of 72.50 ± 2.0%. In the DSP2, a nanofiltration unit was included after the pre-purification step, which resulted in a higher lactic acid purity of 82.0 ± 1.5% but compromising the recovery, i.e. 65.0 ± 1.5%. Overall, the results of the present study indicate the feasibility to use municipal biopulp as a low-cost feedstock for lactic acid production, and thus efforts should be focused to optimize the fermentation and DSP2 steps.