Phosphorus removal in a vertical up-flow constructed wetland
Notice bibliographique
Résumé
Accelerated eutrophication of freshwater ecosystems led by agricultural activities has raised concerns in Southern Quebec and other industrialized locales. Phosphorus being the main culprit, effort has been made to rationalize application and curtail exports of this nutrient with agricultural best management practices. Still, concentrations of phosphorus and nitrogen in typical tile drainage return flow wastewater exceeds the eutrophication-prevention criterion set by the Quebec Ministry of Environment (0.030 mg TP ∙L-1) and the ecosystem safeguard criterion suggested in the literature (1.10 mg TN ∙L-1), with cumulative loads becoming a major contributor to the poor quality of downstream aquatic ecosystems, especially when poorly diluted, as is the case with heavily drained agriculture-dominated watersheds.As a third line of defense in a best management practices package, constructed wetlands (CWs) for the interception of phosphorus are proposed. These wetlands can also mitigate nitrogen and contribute other ancillary benefits. They can be implemented at the mouth of tile drainage or at the confluence of a few outlets, i.e. drainage ditches or first order streams.The main phosphorus removal mechanisms in a CW are adsorption and precipitation with positively charged ions contained in the substrate (e.g., Ca2+, Fe3+, Al3+). Physico-chemical conditions prevailing in the system – especially redox potential – are major factors influencing these reactions. A sub-surface vertical up-flow system seems most appropriate, as it maximizes potential interaction of pollutant-charged water with the substrate constituents, allowing full radial contact and deterring preferential flow. These wetlands also are efficient longer into the cold season, given the underground nature of the flow. An experiment was conducted on McGill's CW research site, situated in Ste-Anne-de-Bellevue, Québec, so as to ascertain the efficiency of a vertical up-flow constructed wetland in treating tile drainage return flow wastewater. During 14 weeks, the capacity to remove the different forms of phosphorus was evaluated, as was the removal of nitrogen compounds. The effluent quality was also compared to the criteria. The wetland had a dimension of 9.15 m2 and the target flow rate was 1 L∙min-1, which is representative of a drainage system serving a 3 ha field in typical Southern Quebec conditions (wetland:watershed ratio: 0.03%; hydraulic loading rate: 0.16 m∙d-1; hydraulic retention time: 2.99 days). The target influent concentrations were 0.300 mg TP ∙L-1, and 10.00 mg TN ∙L-1, which – again – is typical of Southern Quebec tile drainage return flow. The wetland was efficient at removing 84% TP and 86% TN, but the treated wastewater was still above the criteria in 76% and 69% of the cases for TP and TN, respectively.Recommendation is made to supplement the wetland with a dedicated phosphorus-removal substrate so as to further enhance its performance, and to increase the wetland:watershed surface ratio to abate more nitrogen compounds. Community support is key to the implementation of agricultural best management practices. Hence, suggestion is made to include constructed wetlands in the set of initiatives that are financially aided through governmental programs, such as Prime-Vert of Québec.
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Prédiction machine sur la base complète
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Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».