A direct treatment of river waters with ultrafiltration is not yet realised in larger scales due to considerable fouling and scaling effects caused by water contaminants on the membranes surface under those circumstances. Therefore, the deposits on the membrane cannot be eliminated extensively by conventional backwashing. An extensive detachment of the formed layers while backwashing is desired to achieve cost advantages when using the process combination flocculation/ultrafiltration for the direct treatment of surface waters. Hence, pilot and laboratory plant experiments were carried out while dosing different coagulants at different pH-values with different concentrations of the coagulant to investigate their influence on the build-up of the coating layers. The experiments described here were focused on the following questions. Firstly, how do coagulation and flocculation conditions influence the performance of the treatment combination flocculation/ultrafiltration and which coagulant is best? Secondly, does a good operational performance of the combination flocculation/ultrafiltration at laboratory scale coincide with good operational performances at the pilot plant or does the presence of dissolved organic carbon (DOC) in the raw water decrease the performance significantly? Thirdly, does a good operational performance coincide with an extensive reduction of DOC, or humic substances, respectively?

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