Organic fraction of municipal solid waste for the production of L-lactic acid with high optical purity

Abstract

The organic fraction of municipal solid waste (OFMSW) is an abundant biowaste with great potential in the bioeconomy model. Previous reports have demonstrated that OFMSW hydrolysates are good substrates for lactic acid (LA) production. However, LA can exist in two enantiomeric forms (L- and D-) and most commercial LA applications require a high enantiomeric purity, typically of the L-isomer. Due to natural occurring bacteria in the waste, a mixture of D- and L-LA can form in the substrate, reducing the final enantiomeric purity of the product and limiting its commercial application. In the research reported in this article, hydrolysates from OFMSW were evaluated for the production L-LA with high enantiomeric purity. Firstly, a pre-treatment with monopolar electrodialysis membranes was implemented to remove the unfavourable D-LA in the hydrolysate. This step allowed the reduction in LA concentration and subsequent fermentations of the hydrolysate resulted in enantiomeric purities over 98%. At the pilot scale, a fermentation of the pre-treated hydrolysate, by B. coagulans A166, resulted in a final LA concentration of 61.1 g L−1 and a yield of 0.94 g g−1. The downstream of the process resulted on a LA recovery of 51.5% and a L-LA optical purity of 98.7%.