Effects of porous media, macrophyte type and hydraulic retention time on the removal of organic load and micropollutants in constructed wetlands.

The performance of horizontal subsurface flow constructed wetlands in the removal of micropollutants from a wastewater treatment plant effluent was evaluated at mesocosm level. Fifteen mesocosms were studied following a modified Latin Square experimental design with six additional points. Three variables at three levels were studied: porous media -PM- (river gravel, fine volcanic gravel and coarse volcanic gravel), macrophyte type -M- (Thypa latiffolia, Phragmites australis, and Cyperus papyrus) and hydraulic retention time -HRT- (1, 3 and 5 days). As response variables the removal percentages of the total organic load of the effluent (BOD5) and the loads of several micropollutants (caffeine, galaxolide, tonalide, alkylphenols and their monoethoxylates and diethoxylates, methyl dihydrojasmonate, sunscreen UV-15 and parsol) were used. The results showed that the systems remove between 70% and 75% of the organic load and that all the micropollutants were degraded at different extents, from 55% to 99%. The HRT was the variable that showed major effects on the treatment process, while M and PM showed no statistically significant differences in the used experimental conditions.