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Lactic acid production from recycled paper sludge: Process intensification by running fed-batch into a membrane-recycle bioreactor

Marques, S., Matos, C.T., Gírio, F.M., Roseiro, J.C., Santos, J.A.L.
Biochemical engineering journal 2017 v.120 pp. 63-72
Lactobacillus rhamnosus, bioreactors, biorefining, cost effectiveness, enzymes, feedstocks, fermentation, fermenters, filtration, lactic acid, lignocellulose, models, pulp and paper sludge, recycled paper, saccharification
Production of lactic acid from recycled paper sludge by simultaneous saccharification and fermentation (SSF) has previously been implemented under a pulsed fed-batch mode. However, lactic acid concentrations above 58gL⁻¹ inhibit cultivation of the Lactobacillus rhamnosus strain used. Thereby, the present work targeted process intensification by running it into a membrane-recycle bioreactor, providing product removal together with reuse of enzymes and bacterial cells.A shear-enhanced flat sheet cross-flow filtration system was built, working properly with the high-solids concentration suspension. Based on product inhibition and solids concentration constraints, a model was proposed for operation of the membrane-recycle bioreactor. SSF should be run in batch mode into the fermentor for 48h, and then switch-on recirculation through the filtration module, with pulsed fed-batch addition of recycled paper sludge.This innovative approach can be applied to improve other SSF processes dealing with high-solids concentrations, towards cost-effective lignocellulosic feedstock biorefineries.