The major goal of this work was to evaluate the ability of two commercially available nanofiltration membranes (NF) to efficiently separate a mixture of carboxylic acids while simultaneously retaining sugars in actual lignocellulosic biomass digestion liquor. The process achieved separation by high sugar rejection ( >90%) and low acid rejection (0-40%), with the exception of butyric acid (100% rejection). Lower pH led to a significantly lower acetic and lactic acid rejection. The recovery of acids was further enhanced by operating at low pressure. Salt addition did not have a strong influence On acid and sugar rejection, integrating separation with digestion recovered 86% of the acid during a 21 day digestion run, reducing acid concentration in the digestate by nearly 90% relative to a control without acid removal. These results demonstrate proof of concept for use of NE based anaerobic membrane bioreactors to recover carboxylic acids produced from the lignocellulosic carboxylate platform. (C) 2015 Elsevier B.V. All rights reserved.