Comparative pilot study of the performances of two constructed wetland wastewater treatment hybrid systems

Abstract: For small settlements sanitation, constructed wetland systems offer a suitable social economic alternative to the classic wastewater treatment plants. In order to study the treatment mechanisms occurring in the soil–plant system, we set up a small-scale pilot wastewater treatment plant composed by a settler/digester followed by two trains combining two different types of subsurface flow constructed wetlands called ‘hybrid systems’. The first train represents a combination of a vertical flow reed (Phragmites australis) bed followed by a horizontal bed, planted with Typha, whereas in the second one, the combination is reversed. The hybrid systems are fed intermittently with a hydraulic load of 0.2 m per day given in two sequences of one hour separated by a six-hour rest period. We followed the quality of the effluent at the outlet of the beds. The two hybrid systems present satisfactory performances: yields higher than 90% in organic matter removal are registered. For the first system we could obtain a substantial nitrification but uncompleted denitrification whereas for the second system we observed that the total nitrogen (NTK) reduction was achieved by denitrification and nitrification remains almost complete. The pathogenic bacteria abatement is satisfactory for the two systems but more remarkable for the second (2 u log). [Copyright &y& Elsevier]