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

ABSTRACT

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.

GRAPHICAL ABSTRACT

KEYWORDS:

• Treatment wetlands
• organic loading rate
• hydraulic conductivity
• clogging
• principal component analysis

Acknowledgements

We are grateful to the Coordination for the Improvement of Higher Education Personnel (CAPES) and to the National Council for Scientific and Technological Development (CNPq), Brazil.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Alexandre Atalla http://orcid.org/0000-0001-9100-3175

Catiane Pelissari http://orcid.org/0000-0002-2393-6771

Mariana Antonio de Souza Pereira http://orcid.org/0000-0002-9415-5374

Priscila Sabioni Cavalheri http://orcid.org/0000-0002-6925-360X

Pablo H. Sezerino http://orcid.org/0000-0002-2249-0878

Fernando Jorge Correa Magalhães Filho http://orcid.org/0000-0001-5447-0137