After intensive pilot plant tests the treatment scheme for the waterworks Halle-Beesen was designed. In this waterworks river bank filtrate and pretreated slow sand filter infiltrate of the river "Saale" and the river "Weisse Elster" are treated. Both rivers show a high organic load with natural as well as with anthropogenic organic material. To ensure a save disinfection ozonation is part of the treatment. It had to be taken into account, that the bromide content in the raw water is arround 0.5 mg/L. Practical experience over a year period proved, that an optimized ozone dose in combination with the limitation of the contact time lead to a safe disinfection, even under the condition that the bromoform and bromate formation have to be limited. Basic laboratory tests were carried out to investigate the influence of ozonation on the THM formation after final chlorination. The German standart of 10 ng/L for THM's after treatment can be achieved, if the DOC concentration is below 2.0 mg/L.
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