Structural Changes in French VF Treatment Wetland Porous Media during the Rest Period: An Ex Situ Study Using X-ray Tomography

Clogging constitutes a major operational issue for treatment wetlands. The rest period is a key feature of French Vertical Flow (VF) treatment wetlands and serves to mitigate clogging. An ex-situ drying experiment was performed to mimic the rest period and record structural changes in the porous med...

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Bibliographic Details
Published in:Water (Basel) 2021-02, Vol.13 (3), p.389
Main Authors: Martinez-Carvajal, German Dario, Oxarango, Laurent, Adrien, Jérôme, Molle, Pascal, Forquet, Nicolas
Format: Article
Language:English
Subjects:
Biosolids
Clogging
Composition
Computed tomography
CT imaging
Drying
Earth Sciences
Endoscopy
Environmental Engineering
Environmental Sciences
Geophysics
Gravel
Identification and classification
Measurement
Microporosity
Mineralization
Morphology
Particles
Permeability
Porous media
Sciences of the Universe
Soils
Testing
Thickness
Vertical flow
Water treatment
Wetlands
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Summary:Clogging constitutes a major operational issue for treatment wetlands. The rest period is a key feature of French Vertical Flow (VF) treatment wetlands and serves to mitigate clogging. An ex-situ drying experiment was performed to mimic the rest period and record structural changes in the porous media using X-ray Computed Tomography (CT). Samples containing the deposit and gravel layers of a first stage French VF treatment wetland were extracted and left to dry in a control environment. Based on CT scans, three phases were identified (voids, biosolids, and gravels). The impact of the rest period was assessed by means of different pore-scale variables. Ultimately, the volume of biosolids had reduced to 58% of its initial value, the deposit layer thickness dropped to 68% of its initial value, and the void/biosolid specific surface area ratio increased from a minimum value of 1.1 to a maximum of 4.2. Cracks greater than 3 mm developed at the uppermost part of the deposit layer, while, in the gravel layer, the rise in void volume corresponds to pores smaller than 2 mm in diameter. Lastly, the air-filled microporosity is estimated to have increased by 0.11 v/v.
ISSN:2073-4441
2073-4441
DOI:10.3390/w13030389