Microbiological evaluation of constructed wetlands and solar disinfection in wastewater treatment and reuse.

The objective of this study was to evaluate the removal of fecal indicator bacteria and select bacterial pathogens (total coliforms, Escherichia coli, Shigella spp., Salmonella spp. and Pseudomonas aeruginosa) in vertical flow constructed wetlands (VF-CWs) with earthworms and solar disinfection (SODIS) as post-treatment of effluent from a septic tank. There was no significant difference between them in removing bacteria using a VF-CW with earthworms (VF-CW W/E) and without earthworms (VF-CW N/E). Both VF-CWs did not completely remove pathogens; however, with the SODIS technology receiving the effluent from VF-CW W/E, for E. coli, Shigella spp., Salmonella spp. and P. aeruginosa, the values were reduced below the limit of detection and 4.3 log unit average reduction for total coliforms, with 6 h in SODIS.

Influence of earthworm presence and hydraulic loading rate on the performance of vertical flow constructed wetlands.

In order to know the behaviour 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 cm², 0.75 m deep, with sand as filter media and planted with Heliconia rostrata) operated with a variable hydraulic and organic loadings rates (200 mm d-1/123 g COD m-2 d-1; 280 mm d-1/186 g COD m-2 d-1; 160 mm d-1/94 g COD m-2 d-1). Although the efficiency of COD load removal was similar (around 70%) for both CWs, the efficiency of total nitrogen load removal was around 95% throughout the evaluated period. The nitrification-denitrification process was identified with and without the presence of earthworm. VF-CW with earthworms showed higher hydraulic conductivity values (from 0.11 to 0.14 m h-1) compared with the VF-CW wetland without earthworms (0.07-0.09 m 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.