In a full-scale approach, we investigated whether nitrification can be carried out in partially aerated flocculation filters without compromising the removal of suspended solids. The objective is an aerated filter in addition to an advanced nitrification in the main biological treatment step to reduce low NH4-N concentrations in the effluent to very low concentrations. In two separate sets of experiments with an aerated filtering layer of 0.7 m and 1.4 m, nitrification rates up to 14 g N/(m3/h) were achieved. Compared to unaerated chambers, there was approximately the same removal of particulate COD and of precipitated phosphorus compounds. Due to the formation of anoxic zones, nonspecific denitrification occurred in the chambers under both conditions. Decay products are suspected to be the endogenous H-donors.

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