The filtration efficiency of spacer filled membrane module is limited by the poor hydrodynamic condition near the spacer filaments contacting the membrane. To mitigate this negative effect, a saw-tooth spacer (STS) is proposed in this paper. The flow patterns in the STS filled membrane channel were tested and compared with that in the conventional zigzag spacer (ZS) filled membrane channel by Particle Image Velocimetry (PIV) and the hydrodynamic mechanism for filtration improvement was revealed. The results showed that compared with the ZS, stronger turbulence can be produced by the STS due to the periodic generation and break of the recirculation region in the membrane channel. At the feed flow Reynolds number (Re) ranging from 750 to 1875, the average membrane shear rates in the STS membrane channels were more than 638 times higher than that in the conventional ZS membrane channel and increased with the tooth height. The stagnation region and recirculation region near the membrane surface which can result in serious membrane fouling were avoided in the STS membrane channels. Filtration experiments were performed and the results showed that higher steady flux can be obtained in the membrane module filled with the STS than that filled with the ZS. (c) 2015 Elsevier B.V. All rights reserved.