Sludge Dewatering Using Macrophytes in a Small Wastewater Treatment System: A Case Study of a Pilot Scale Plant in Northern Italy

Abstract

A study was conducted on a system consisting of two beds of 12 m2 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-NH4- 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.

Sludge drying reed beds: full- and pilot-scale study for activated sludge treatment

“…The sizing of SDRBs is roughly based on the sludge production, its quality and the organic load acceptance (Nielsen 2003). Several investigations have been done on dewatering and mineralization efficiencies of SDRBs used for activated WWTP (Mellstrom & Jager 1994;Lié nard et al 1995;Lié nard 1999;Begg et al 2001; Barbieri et al 2003;Nielsen 2003Nielsen , 2005 where a general design of 50-60 kg DM m 22 yr 21 (Mellstrom & Jager 1994;Lié nard 1999;Nielsen 2003) with a half load (25 kg DM m 22 yr 21 ) recommended during the commissioning period. The system consists in several beds constructed in parallel and alternately fed which allowed sufficient rest period for dewatering and progressive mineralization of the sludge deposit.…”