Four parallel biofilters were tested for treatment of ozonated humic water. Two of them contained Kaldnes plastic cylinders (KMT media), one marble and one expanded clay aggregates (Filtralite NC) as biofilm media. Dual-media filter was used for removal of bacteria from biofilter effluents. After four months of operation, average TOC removal was 37–38% and CODMn removal was 43–45% in the ozonation/biofiltration process. Ozonation removed 83% of colour from the raw water. Over 83% removal of ozonation by-products (aldehydes and ketoacids) was also achieved. Biofiltration increased the levels of heterotrophic bacteria in the water but they were reduced by 88% in the dual-media filter. The biofilter media did not have significant effect on treatment efficiency at the empty bed contact time of 30–40 min.

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