The objectives of this project were to:quantify the level of contamination of filters by various organisms (amoebae, aerobic spores, E.coli, nematodes, etc.) through a survey performed on several production sites, with various resources andassociated water treatment works;optimize filter washing to prevent or minimize health risks; and,define cleaning protocols in order to allow operators to decontaminate filter media. Protocols havebeen established from tests at laboratory and pilot scale before application on industrial sites.The first part of the study focuses on a worldwide survey of more than 15 filters from water treatment plants (WTPs) in Europe(France, Hungary, United Kingdom) to develop detailed information on filter contamination. The informationcollected includes process design, water resource characterization, and contamination level offilter media and filtered water quality with details on biological particles.Results of this survey revealed a wide variety of organisms causing the contamination of the filters.The mode of contamination of the filter beds (1st stage and 2nd stage filter) is primarily due to theaccumulation of biological particles coming from the resources, and secondarily a consequence of directdevelopment within the filters.Backwashing applied under standard operating conditions (in terms of air, water flow rates andfrequency) efficiently removed organisms retained in the inter-granular space of the filter media during the first two steps; however, backwashing does not efficiently release the organisms (particularly amoebae andzooplankton) protected by the biofilm occurring on the media surface.Regarding the media cleaning, the most appropriate reagents for obtaining elimination oforganisms, particularly amoebae fixed on a media, were chosen through batch tests with variouschemicals (salts, oxidants, acid, base). Salts and oxidants were found to be the most efficientreagents for removal of organisms from the media. Includes 18 references, tables, figures.
