Performance of sludge treatment wetlands using different plant species and porous media.

The aim of this study was to evaluate the dewatering and mineralisation efficiency of three sludge treatment wetlands (STW) configurations differing on plant species (Phragmites australis and Typha sp.) and filter medium (gravel and wood shavings). Sludge dewatering and mineralisation were monitored in three pilots STW for 2 years. The sludge volume was reduced by 80% in all configurations tested, the total solids (TS) increased to 16-24% TS and the volatile solids (VS) decreased to 50% VS/TS. After a resting period of three months the biosolids showed a high stabilisation (dynamic respiration index around 0.26-0.70 mgO(2)/gVS h), caused no phytotoxicity (germination index >100%), and had low heavy metals and pathogens concentrations (E. coli<240 MNP/g; absence of Salmonella). The lack of statistical significance (p>0.05) between the results obtained from the different STW configurations suggests that STW may be either planted with P. australis or Typha sp., and that wood shavings may replace gravel as filter medium.