The biggest advantage of outside-in filtration is the capability of handling very high suspended solids. All the commercially available hollow fiber modules for MBR run at outside-in modes. These modules are directly immersed in mixed liquor without pressure vessel, where feed water (mixed liquor) contacts the shell side of the membrane and permeate is collected in the lumen by vacuum. Air scouring is performed either continuously or intermittently in the shell side to prevent solids accumulation on membrane surface. ZW500 (GE Water), MemPulseTM (Semens), MUNC-620A (Asahi Kasei), etc. fall into this category.