Domestic wastewater treatment with a vertical completely drained pilot scale constructed wetland planted with Amaranthus hybridus

Abstract

A pilot scale constructed wetland planted with Amaranthus hybridus was developed for domestic wastewater treatment. The reactor system was composed of rectangular beds realized in cement. Each
bed was filled from the bottom to the top with 0.1 m of gravel (15/25 mm) and 0.30 m of a white sand originating from the Ebrié lagoon. Two beds planted with yang A. hybridus plants (high density: 40
plants/m²; low density: 10 plants/m²) and one control (unplanted bed) were used to perform the experiment. The pH of the overall filtrates decreased from 7 to around 8. Planted beds gave best COD
removal (high density = 70%, low density = 66%) than the control (60%). Globally nutrients were best removed in the planted beds (NH4
+: 69%, PO4 3-: 67%) than in the control (NH4
+: 15%; PO4 3-: 56%). However the important oxidation of NH4
+ to NO2 - and NO3 - provoked their accumulation in these beds
filtrates than in the control. The increase of the plant density seems to have any statistical significant impact upon pollutants removal between the two planted beds experimented. But augmenting plant
density allows increasing the beds removal capacities. Plants leaves were less contaminated at 0.5 m height, suggesting it for their harvesting.