Removal of suspended solids from raw water is a basic technology in water treatment to prevent rapid growth of cake layers. The conventional technology used for removal consists of coagulation, sedimentation and filtration systems. However, when the quality of raw water changes, the suspended solids leak into filtered water, often fouling subsequent RO membrane modules. If we can substitute a conventional pretreatment system with membrane separation technology, the subsequent RO fouling will be eliminated and stable operation will become possible. At the same time the system will also be simplified. However, there have been no appropriate membrane modules applicable for pretreatment systems, and very few attempts have been made to replace the coagulation, sedimentation and filtration process with membrane systems. We have succeeded in developing a new spiral membrane module which can directly feed the raw water containing suspended solids. Due to its construction with through water channels, this module is applicable to the direct feeding of the raw water containing a large quantity of suspended solids, promising the possible development of its new applications. However, the requirement for the application of this membrane separation technology to water treatment is the reduction of operational cost, that is, an increase in the filtration flux of the membrane module. We studied how to increase the filtration flux from three viewpoints: promotion of turbulent flow in raw water, coagulation effect and membrane backwashing. As a result, we found that intermittent membrane backwashing combined with turbulent flow promotion is an effective means to maintain high filtration flux of the membrane module.
