Recent innovations in Norway regarding coagulation-contact filtration for the removal of natural organic matter (NOM) include chitosan as a natural and biodegradable coagulant, and filter media based on lightweight expanded clay aggregates (Filtralite). The main advantages associated with chitosan are: reduced solids production compared with conventional coagulants; and treatment and disposal of natural, biodegradable sludge, which does not contain metal hydroxides from metal-based coagulants. Filtralite can be produced with an inverse relationship between grain size and density, thus allowing an approximation to the ideal situation of decreasing grain size in the direction of flow. Traditionally, this important property of a filter bed is utilised in up-flow filters, or in dual or multimedia down-flow filters with combinations of two or more filter media. This paper presents experimental results from pilot-scale treatment of NOM-containing raw waters using chitosan for coagulation and expanded clay aggregates as filter media. A dual media anthracite-sand filter and alum coagulant was used as a reference for comparison with conventional process configurations.

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