Fixed Biomass Carriers in Activated Sludge Plants

To upgrade existing activated sludge treatment plants, the effect of submerged elements in the aeration basins was verified. In a full scale unit, one complete section of the plant fitted with biofilter packing was operated in parallel with a similar unmodified section as reference. The volume occupied by the fixed beds was varied between 20 and 40 % of the tank. The biofilm evolution and hydraulic behaviour of the packing was followed. No significani change in sludge settleability was observed, but fixed biomass addition reduced sludge production. The submerged elements improve removal efficiency at higher loads. Effluent quality can be maintained even though loadings are increased. Existing treatment plants can thus be adapted to higher loads without additional basin volume. For a constant loading, the basins with biomass carriers improved residual pollution values. Higher purification standards can thus be met without increasing plant capacity.