Secondary effluent from a bleached kraft mill activated sludge plant was treated in a pilot scale fluidized bed to remove residual organic carbon and AOX. Granular activated carbon was used as an adsorbent and support material for biomass. Physical adsorption and biodegradation were followed in a period of 18 weeks. Reduction of dissolved organic carbon was 57% throughout the period, mean load being 0.9 g of DOC/kg activated carbon in a day. AOX removal was more efficient, 70-90%. Reduction rate decreased in the course of time but could be partly recovered with addition of nutrients (P, N) to the nutrient deficient feed. A parallel experimental reactor was regenerated with ultrasonication/infrared - treatment. Physical regeneration gave a remarkable but temporary increase in the removal rate. A stable share of the total removal of DOC, 20-30%, was due to biodegradation and bioregeneration.

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