Lactic acid production from recycled paper sludge by simultaneous saccharification and fermentation

Concentrated sludge generated in large amounts by the wastewater treatment facilities of recycling paper plants raises a serious disposal problem requiring urgent solution. This recycled paper sludge (RPS) is an industrial waste with high polysaccharide content. As previously demonstrated, cellulosic and hemicellulosic fractions of RPS can be completely converted by enzymatic hydrolysis (using Celluclast®1.5 L with Novozym®188) into the constitutive glucose and xylose. These monosaccharides can be used on fermentation media to obtain a variety of products, such as lactic acid, which has an expanding market as precursor of biodegradable polylactides. Hence the purpose of the present work is to evaluate the performance of RPS as feedstock for fermentative production of lactic acid (LA) with Lactobacillus rhamnosus ATCC 7469, a very efficient lactic acid bacterium. Maximum production of lactic acid from RPS was obtained by performing the hydrolysis and fermentation steps simultaneously on medium supplemented with MRS components and calcium carbonate. L. rhamnosus produced 73 g L−1 of lactic acid, corresponding to a maximum productivity of 2.9 g L−1 h−1, with 0.97 g LA produced per g of carbohydrates on initial substrate. A process simplification was also implemented by minimizing RPS supplementation and suppressing Novozym cellobiase addition.