Process for sterilizing a filtration device

Claim 1

A process for sterilizing a filtration device containing residual raw water and filtrate and having a raw water side and a filtrate side and which employs therein a hollow, fiber type filtration module comprising hollow fibers disposed in a module case, said hollow fibers having end portions which are fixed in said module case by a sealing material, said hollow fibers being made of a heat resistant polymer with a heat distortion temperature of 70° C. or higher under a load of 18.6 kg/cm 2 and containing a pore diameter of less than 0.45 μm and the sealing material having a diference in the average linear expansion coefficient between it and the material of the module case of 7×10 -5 /°C. or lower, at a temperature of 20°-121° C., which comprises (i) discontinuing filtration, (ii) passing sterilizing steam from the raw water side of the module to the filtrate side thereof, after pushing out the raw water from the raw water inlet of the module and filtrate from the module, with said sterilizing steam and (iii) preventing the filtrate side of the filtration device from developing a negative pressure by introducing a fluid selected from the group consisting of water and a sterilized gas into the filtration device from a raw water side during the natural cooling which takes place after the steam sterilization has been completed.