Evaluation of the e ectiveness of horizontal subsurface flow constructed wetlands for di erent media

Two media bed (gravel and Filtralite NR) were tested in a mesocosm to evaluate the removal of organic matter (as chemical oxygen demand (COD)), ammonia (NH4-N), nitrite, nitrate and solid matter (as total suspended solids (TSS)) for a synthetic wastewater (acetate-based) and a domestic wastewater. The use of Filtralite allowed average removal rates (6-16.8 g COD/(m2·day), 0.8-1.1 g NH4-N/(m2·day) and 3.1 g TSS/(m2·day)) and removal efficiencies (65%-93%, 57%-85% and 78% for COD, NH4-N and TSS, respectively), higher than that observed in the experiments with gravel. The applied loads of COD, ammonia, nitrate and TSS seem to influence the respective removal rates but only for the treatment of domestic wastewater with higher correlation coefficients for Filtralite. Regardless the type of media bed and the type of wastewater, nitrate was completely removed for nitrogen loading rates up to 1.3 g NO3-N/(m2·day). There was no evidence of the influence of nitrate loads on the removal of organic matter.