Previous research has demonstrated that powdered activated carbon (PAC), when applied at very low dosages and long SRTs, reduces membrane fouling in membrane bioreactor (MBRs). This effect was related to stronger flocs which are less sensitive to shear. Low temperature and high salt concentration are known to drastically decrease the filterability of the sludge. In this paper the effect of PAC addition on the robustness of MBR when submitted to these disrupting conditions was investigated. PAC amended sludge showed a higher resistance to high salinity with a lower fouling development and release of foulants. When submitted to lower temperatures, the sludge without PAC showed a clear decrease of the filterability, while the filterability of PAC amended sludge was much less affected. PAC addition does not only improve the filterability in the MBR under normal conditions but also when the sludge is submitted to stress. A low PAC dosage could be used during startup and difficult conditions (e.g. winter) to minimize detrimental effects of such conditions. (C) 2011 Elsevier B.V. All rights reserved.