This study describes the experience received in operating ail SM-SBR under different hydraulic retention times for the treatment of synthetic greywater. The pilot scale SM-SBR with a working Volume of V-R = 500 L is operated with hydraulic retention times of 33, 24 and 12 h, and a volumetric exchange ratio of similar to 0.25. The removal of COD, ammonia, total nitrogen is investigated for the different set-ups. Despite the low COD in greywater, the treatment performance of the reactor is always sufficient to meet reuse guidelines. The biomass concentration increases slowly, although no excess sludge has been taken Out (except sampling). Therefore, the sludge age is assumed to be >360 d.