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Towards non-contact pollution monitoring in sewers with hyperspectral imaging

Headwall MV.X VNIR hyperspectral imaging system over a wastewater specimen.
Headwall MV.X VNIR hyperspectral imaging system over a wastewater specimen.

Monitoring water quality in sewers is challenging, particularly because state-of-the-art technologies require contact with the raw wastewater. The presence of fat, oil, grease and solids makes automated grab sampling difficult and causes sensor fouling. To overcome these limitations, non-contact methods based on light reflectance, such as hyperspectral imaging (HSI), are gaining attention. However, HSI has never been tested for raw wastewater. To assess its accuracy for measuring pollution, we developed a laboratory setup and performed targeted experiments with a combination of raw and diluted wastewater, as well as synthetic turbidity stock solutions.

We measured seven pollution variables: chemical oxygen demand, turbidity, dissolved organic compounds, ammonium, total nitrogen, phosphate, and sulphates. We used automated pixel selection and partial least squares regression to retrieve pollution information from the hyperspectral images.

Our results, based on 144 samples, suggest that HSI can estimate pollution levels with a precision in the range of state-of-the-art absorbance spectroscopy methods. Additionally, we found that the combination of pixel and wavelength selection, enabled by the hyperspectral data structure, significantly influences the performance of partial least square modelling. Overall, our findings indicate that hyperspectral imaging is a promising technology for non-contact monitoring of water quality in raw wastewater.

Authors:

Lechevallier P., Villez, K., Felsheim C., Rieckermann J.

Published in:

Environ. Sci.: Water Res. Technol., 2024, Accepted Manuscript

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