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BACKGROUND A major cost in acid-catalysed hydrolysis of biomass to fermentable sugars is the consumption of acid itself. In this study, a combined process was developed in which the acid and sugar in the hydrolysate were separated using an acid retardation process and then the dilute aqueous product streams were concentrated using a continuous-effect membrane distillation ( CEMD) process, thus acid could be reused as catalyst. RESULTS The recovery rate of sugar was as high as 94.3-99.2% while the recovery rate of sulfuric acid was 92.4-98.9%. The eluents were further concentrated using the CEMD process. When a solution of 2 wt% sulfuric acid was concentrated to c. 40 wt%, the maximum value of permeation flux ( Jw) and gained output ratio ( GOR) was 6.20 L m−2 h−1 and 15.50, respectively. Meanwhile, the dilute aqueous sugar solution obtained from corn stover was concentrated 20-fold to a final concentration of c. 497.6 g L−1 using the CEMD process with a final GOR of 5.5. CONCLUSION The combination of acid retardation and CEMD is suitable for the production of sugar, further purification and concentration of eluents; the sugar solution can be used for fermentation and acid solution can be reused as catalyst. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]