Environmental technology | 2019
Influence of earthworm presence and hydraulic loading rate on the performance of vertical flow constructed wetlands.
Abstract
In order to know the behavior and performance of a vertical flow constructed wetland (VF-CW) operating with earthworm, this study evaluated the earthworm presence linked to hydraulic loading rates applied for domestic wastewater treatment. Two VF-CW units (710\u2005cm², 0.75\u2005m deep, with sand as filter media and planted with Heliconia rostrata) operated with a variable hydraulic and organic loadings rates (200\u2005mm d-1 / 123\u2005g COD m-2 d-1; 280\u2005mm d-1 / 186\u2005g COD m-2 d-1; 160\u2005mm d-1 / 94\u2005g COD m-2 d-1). Although the efficiency of COD load removal was similar (around 70%) for both CWs, the efficiency of total nitrogen (TN) load removal was around 95% throughout the evaluated period. The nitrification-denitrification process was identified with and without presence of earthworm. VF-CW with earthworms (VF-WE) showed higher hydraulic conductivity values (from 0.11 to 0.14\u2005m h-1) compared with the VF-CW wetland without earthworms (VF-NE) (0.07 to 0.09\u2005m h-1). This study showed that the use of earthworms in CWs can be associated mainly with a preventive measure of clogging, which requires measures to maintain earthworms inside the bed media. Additionally, the earthworm presence has an ingestion mechanism of organic and inorganic solid particles in wastewater which excretes them as finer particles.