Performance of vegetated and non-vegetated vertical flow reed beds in the treatment of diluted leachate.

ABSTRACT

This study was undertaken to investigate the behaviour of a vertical flow reed bed system with 3 kind of wastewaters (W1, W2 and W3) and for two hydraulic retention times (3 and 7 days) as well as to assess the role of Phragmites Australis in constructed wetland treatment processes. The adopted batch experimental system consisted of six vertical flow filters, filled with granular media and planted with reeds. For each vegetated reactor there was a correspondent blank in order to make a comparison. Wastewaters were obtained mixing tap water, MSW landfill leachate and activated sludge in different percentages. W1, W2 and W3 were designed in order to reproduce treated or untreated wastewaters not in compliance with legislation in force (Directive 91/271/EEC), with increasing level of NH4+-N from W1 (16.3 mg/L) to W3 (76.0 mg/L). In average terms, 3 days was sufficient for W1 and W2 to face the compliance limits; while, for W3 even 7 days was not sufficient to respect the compliance limit for ammonia nitrogen (1.4 times greater). The obtained results shown that the vegetation played an essential role especially in the removal of nitrogen for the wastewater with the highest loads the contribution of reeds in the removal of nitrogen was greater than that of biofiltration processes. The contribution of the vegetation was also detectable in the removal of orthophosphate, but with minus efficiency.