Within the scope of a research programme into wastewater treatment scenarios based on physical-chemical pretreatment, the application of direct influent filtration (DIF) as a first treatment step in a wastewater treatment system was investigated. The aim of the experimental research was to investigate the feasibility of DIF as a pretreatment step for advanced particle removal. With a large scale pilot-plant filter at WWTP Leiden-Noord, The Netherlands the removal characteristics for suspended and colloidal material were investigated as well as operational conditions of eight different filter configurations. From the experimental research it was concluded that filtration of raw wastewater is possible, notwithstanding the relatively short runtimes due to clogging. In general, the filters produced a filtrate with a constant quality with low concentrations of solids and low turbidity. Without addition of chemicals hardly any colloids and solubles were retained, but only suspended particulates were removed. After dosage of iron or polymer, it was possible to remove more suspended matter and a high proportion of colloidal material. Finally it was concluded that DIF could be applied as a compact treatment system to produce a high quality primary effluent with a constant composition, but for practical application further research has to be done.

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