Sunday, April 29, 2007

Lactic acid production from recycled paper sludge

S. Marques1, J. A. L. Santos2, F.M. GÝrio1, and J.C. Roseiro1. (1) Biotechnology Department, INETI, Estrada do Pašo do Lumiar, 22, 1649-038 Lisboa, Portugal, (2) IBB-Institute for Biotechnology and Bioengineering, Centre for Biological and Chemical Engineering, Instituto Superior TÚcnico, 1049-001 Lisboa, Portugal

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®1.5L 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 lactic acid production.
Five lactic acid bacterial strains were screened for lactic acid production, and Lactobacillus plantarum ATCC8014 and Lactobacillus rhamnosus ATCC7469 were selected for further studies with RPS.
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. plantarum and L. rhamnosus produced 72 and 73 gL-1 of lactic acid, corresponding to a maximum productivity of 3.7 and 2.9 gL-1h-1, respectively, with more than 0.95g LA produced per g of carbohydrates on the initial substrate.
A process simplification was also implemented by minimizing RPS supplementation, suppressing Novozym cellobiase and CaCO3 addition (provided non-neutralized RPS is used).
In conclusion, lactic acid production from RPS is feasible and the biological process may represent an opportunity for solving an environmental problem while producing a commercial product from a substrate of negative cost.