The process combination of in-line coagulation and subsequent membrane filtration is a suitable advanced treatment stage to achieve higher quality standards regarding pathogens and phosphorus in biologically treated wastewater prior to its discharge into sensitive water bodies. In this study a membrane pilot installation (capacity of 6 m3/h) was operated in dead-end configuration to investigate phosphorus removal and fouling behaviour depending on FeCl3 dosage. In parallel, effects of in-line coagulation on the filtration behaviour were investigated in lab-scale filtration experiments. The coagulation leads to the predominant reduction of dissolved organic macromolecular substances which are detected as biopolymer fraction by liquid chromatography-organic carbon detection. Besides the removal of dissolved organic molecules, the resulting filter cake plays a major role for the performance of ultrafiltration. In lab-scale filtration experiments the in-line coagulation results in positive effects on the filtration stability. In contrast, high coagulant doses lead to the loss of filtration performance during the pilot operation. The installed in-line coagulation, however, successfully reduced the orthophosphate concentration in permeate to values below 30 μgP/L when operated at a fixed molar ratio of FeCl3 concentration to influent PO4-P concentration of 6 (ßPO4-P-value).

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