A study was conducted on a system consisting of two beds of 12 m 2 each, planted with reeds and filled with sludge from an activated sludge plant dimensioned for 3000 p.e. During 2001, 10 kg of TS/m2 were loaded in each bed using sludge with a dry matter content of 3% during winter and of 0.5% in summer. The aim of the study was to evaluate parameters such as: COD, TSS, P-PO4 3-, N-NO2 -, N-NO3 -, N-NH4 - in percolation water, the dewatering capability of the two beds and to estimate N mass balance. The observations on dewatering process showed that dried sludge reached a content of 23% TS in winter and of 30% TS in summer. During summertime the plant did not release any percolation flow; in the rest of the year the concentrations of COD, TSS, P-PO4 3-, N-NO2 -, N-NH 4 - remained within bounds of the European directive (91/271/CEE). The N mass balance proved that 90% of N was removed by the denitrification process.

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