Abstract
Water-shortage will be the largest problem in 21st century, especially in big cities. Population growth will be limited based on amount of usable water. There are two ways to get water resource. One is development of new water resource, such as sea water desalination, and the other is water reuse. New water utilization system with membrane technology is proposed. For tap-water production, membrane separation is used to make water only for cooking (kitchen use) and drinking, and for other purposes such as laundry and bath use, the conventional treatment with flocculation, sedimentation and sand filtration is enough to obtain water quality for these purposes. Waste water from laundry and bath use should be treated by activated sludge with membrane, and the treated water should be reused for toilet. The membrane technology is essential in this system. Development of membrane modules and operation mode for this system will be necessary.
