Examination of COD-degradation and N-conversion within vertical flow systems and determination of influencing factors was done on constructed wetlands as well as on unplanted soil columns at laboratory scale. Topics of investigation were influent and effluent concentrations and removal efficiency of vertical flow beds, soil water composition at different depths and N-conversion activity with different operating methods, different hydraulic loadings (50, 100, 150 mm/d) and different soil materials.

The extent of degradation and conversion are especially determined by O2-supply which can be influenced by operating method, hydraulic loading and soil material.

COD-degradation and N-conversion take mainly place in soil depths down to 20 cm depending on the O2-supply and soil material. In general a sufficient O2-supply in an intermittently loaded vertical flow bed leads to a COD- and NH4-reduction ≥ 90% and prevents a Ntot-degradation of more than 50%. The determination of N-conversion activities of different soil samples has shown that nitrification activity as well as nitrate reductase activity have their maximum in soil depths down to 10 cm.

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