The production of D-lactic acid by fermentation from the waste newspapers recycling as the carbon source

Abstract

D-lactic acid (D-LA) is an important substance, which has been used in various end-use industries, including pharmaceuticals, food and milk beverages. Lignocellulose is a desirable material for D-LA fermentation, due to its hydrolysate rich in monosaccharides can be obtained from the wastes to finally achieve high D-lactate yields. In this study, the waste newspapers removed most of the lignin was applied as a carbon source to produce D-LA using Escherichia coli JH15, rice straw hydrolysate and mixed sugars (glucose and xylose) were selected as a control. Compared with rice straw hydrolysate, the waste newspapers hydrolysate as a carbon source for D-LA production has obvious advantages, including high D-LA concentration, fast fermentation speed and no need for detoxified treatment. Compared to the mixed sugars, the D-LA productivity and conversion yield of total sugars to D-LA did not been different significantly using waste newspapers hydrolysate as a fermentation substrate, but the fermentation duration was extended by 6 hours. The fermentation could be finished just after 16 hours in a 7-L fermenter, and the maximum concentration of D-LA reached 33.60 g/L, with a high conversion yield of total sugars to D-LA (0.92 g/g). According to the fermentation performances of the concentration of D-LA, the yield of D-LA, the conversion yield of total sugars to D-LA, the fermentation duration, the waste newspapers hydrolysate as a carbon source for D-LA production is an efficient strategy to enhance the economic feasibility of this bioprocess.