A simplified modelling and a simulation of a membrane-coupled anaerobic bioreactor, AMBR were performed to assess the potential of controlled retention of solutes by the membrane, R, on biomass growth and of purified water quality. R was shown to be a major parameter, which enables to uncouple the hydraulic resistance time, HRT from the solute retention time, independent of biomass retention, and has a significant effect on purified water quality. Therefore, from a theoretical point of view, it facilitates reaching high biodegradation in a small volume membrane reactor. The simulation makes it possible: (i) to anticipate the effect and relative weight of model parameters in the mechanisms that rule the AMBR behaviour and (ii) to identify the AMBR parameters and operating modes in order to avoid reactor washout or overload, amplified by R. From the analysis, it appears that it is possible to use any type of membrane, which at least retain the biomass: (i) low R values using microfiltration or ultrafiltration membranes require long HRT or small influent concentration and larger reactor volume to achieve good water quality: (ii) high R Values using nanofiltration or reverse osmosis membranes, which will retain the solutes as well as the small-degraded molecules within the anaerobic reactor volume, require short HRT for highly purified water, but necessitate a large investment. (c) 2008 Published by Elsevier Ltd.