The influence of growth media on the behaviour of cultured algae in direct filtration was examined. Cultured Chlorella vulgaris and Selenastrum capricornutum on Jaworski and Z-8 media are used for model water preparation. It was found that the same algal species in the same growth phase had different responses under identical treatment conditions. Also, difference in growth phase influenced their behaviour. Therefore, assuming similarity between cultured algae and algae from natural waters is highly questionable.

The efficiency of the direct filtration treatment process for the removal of dominant algal species present in Biesbosch Water Storage Reservoirs was investigated. Different removal patterns were found for various algal species. The most difficult to be removed were Rhodomonas minuta and µ-algae. High removal efficiency was found for Stephanodiscus hantzschii and other cylindrical diatoms. An overall algal biomass removal of 90 % was achieved. Algal penetration through filters is a consequence of algal size and inefficient agglomeration during coagulation. It was found that the application of oxidants (ozone and potassium permanganate) prior to coagulant addition improves the efficiency of direct filtration. The use of H2O2 did not enhance algal removal under the conditions investigated.

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