Experiences With a New Plant for The Treatment of Lake Zurich Water

Abstract

The formation of undesirable by-products of the chlorinated hydrocarbon group shows that chlorine can no longer be used for water treatment in view of the present degree of raw water pollution and the related regulations. There are now possibilities of banning these undesirable substances from drinking water. Chlorine must be totally replaced by ozone. Since 1958, the drinking water derived from Lake Zurich has been treated with ozone. Experience with this method has steadily improved and the excess ozone is now completely removed from the exhausts. The lake water is subjected to preozonation as soon as it enters the treatment works. This ensures that the water is disinfected immediately on entering the works and that the whole chain of treatment is kept as germ-free as possible. It also increases microflocculation and thus reduces the amounts of flocculating substances used. Through the intermediate ozonation before the active carbon filters, these can be used not merely as adsorption filters but also as biological filters. In consequence, the active carbon can remain in use for 10 to 15 years instead of 1 year as formerly.