Bioconversion of wastewater-derived duckweed to lactic acid through fed-batch fermentation at high-biomass loading

Abstract

After being collected from the wastewater treatment system, duckweed biomass which is rich in starch and protein has the potential to be converted to valuable chemicals. This study aimed to establish a fermentation process for bioconversion of duckweed biomass derived from wastewater treatment to lactic acid (LA) by Lactobacillus casei. The Lactobacillus casei CICC 23184 showed the best LA production ability in duckweed-based medium among five strains. Simultaneous saccharification and fermentation (SSF) and separated hydrolysis and fermentation (SHF) were conducted, and the SSF had better performance even with lower enzyme dosage. No extra nitrogen source needed supplying into duckweed-based media. In batch fermentation, biomass loading of 220 g kg−1 was optimal with LA concentration of 72.51 ± 2.81 g kg−1 and yield of 0.35 ± 0.01 g g−1dry biomass. The highest LA concentration (100.36 ± 3.31 g kg−1), yield (0.38 ± 0.01 g g−1dry biomass), and productivity (2.09 ± 0.07 g kg−1 h−1) were obtained through fed-batch SSF at a final biomass loading of 260 g kg−1. This study demonstrated that it is feasible to utilize duckweed biomass as feedstock to produce LA through fermentation, and a fed-batch SSF at high-biomass loading was successfully established. This study provides a novel strategy for sustainable recycling of duckweed biomass derived from wastewater treatment.