Résumés
Abstract
Wastewater conductivity has been monitored for extended periods of time by in situ probes and on grabbed samples in four communities (from 1,000 to 350,000 PE). In parallel, the concentrations of the main ionic contributors, such as calcium, sodium, potassium, magnesium, ammonium, ortho-phosphate, chloride and sulphate have been measured and their variations with respect to time compared to human activity patterns. It appears that sodium, potassium, ammonium and ortho-phosphate, which contribute to about 34% to wastewater conductivity, exhibit diurnal variations in phase with human activity evaluated by absorbance at 254 nm. However calcium (≈ 22% of wastewater conductivity) is out‑of-phase. This release, ahead of the one of other cations and anions, could be related to sewer concrete corrosion or to groundwater infiltration. The combination of these different ionic contributions creates a conductivity pattern which cannot be easily related to human activity. It makes difficult to integrate conductivity in a monitoring system able to detect ion-related abnormalities in wastewater quality.
Keywords:
- Conductivity,
- corrosion,
- urine,
- calcium,
- potassium,
- infiltration
Résumé
Les variations de la conductivité d’eaux usées urbaines ont été suivies sur de longues durées a l’aide de sondes placées in situ en entrée d’installations de traitement et sur des échantillons prélevés automatiquement. Quatre communautés (entre 1 000 et 350 000 habitants) ont été choisies pour cette étude. On a également dosé sur les échantillons les principaux ions (calcium, sodium, potassium, magnésium, ammonium, ortho-phosphates, chlorures et sulfates). Il apparait que le sodium, le potassium, l’ammonium et les ortho-phosphates contribuent pour 34 % a la conductivité des eaux usées et présentent des variations journalicres en phase avec la pollution carbonée soluble, estimée a partir de l’absorbance a 254 nm. Par contre, le calcium, qui contribue pour 22 % a la conductivité, présente un déphasage qui peut ztre du a son transport dans le réseau d’assainissement du fait de la corrosion des conduites en béton ou a des infiltrations d’eaux claires. Finalement, la combinaison de ces différentes contributions ioniques conduit a une variabilité de la conductivité qu’il n’est pas facile de lier a l’activité humaine, et donc a des rejets accidentels dans le cadre d’un systcme de détection de variation anormale de la qualité des eaux usées.
Mots clés:
- Conductivité,
- corrosion,
- urine,
- calcium,
- potassium,
- infiltration
Parties annexes
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