An optimised water treatment system incorporating protection against Cryptosporidium oocysts

The Hanshin Water Supply Authority has been pursuing modifications to its new water treatment system, which accompanies conventional technolog- y with ozonation and activated carbon adsorption. The design criteria of this system aim principally at maintaining a balance between microbial risk management and chemical risk management of the finished drinking water quality. With regard to the protection against Cryptosporidium by our multiple-barrier-train, solid-liquid separation owing to sedimentati- on, filtration and dissolved air flotation, as well as inactivation through ozonation and heating, makes it possible to remove 7 or more log-units of oocysts. An additional cost of changing to the new technology corresponds to 5-6% of Japan's average prime cost of drinking water supply.