Screening analysis of seston from a domestic wastewater treatment plant using digital images

Analytical Methods
Cite this: Anal. Methods, 2012, 4, 2375 www.rsc.org/methods

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Screening analysis of seston from a domestic wastewater treatment plant using digital images
˜ Antonio C. Sousa,a Anderson S. Soares,b Clarimar J. Coelho,c Edvaldo N. Gaiao,d Alessandra F. C. Pereira,e ˜ Roberto K. H. Galvaof and Mrio C. U. Arajo*e a u
Received 26th August 2011, Accepted 5th May 2012 DOI: 10.1039/c2ay05537f This paper concerns the use of digital images of seston to monitor different ponds of a domestic wastewater treatment plant. For this purpose, a commercial camera was employed to photograph the seston samples and an automatic procedure based on the Hough Circle Transform was used to segment the resulting picture. Multivariate techniques were then employed to analyze the seston images in terms of their RGB colour components. The results indicate that such colour components undergo a significant change after each stage of the wastewater treatment process, according to a Hotelling T2 test (p-value smaller than 10À4). This finding was corroborated by the use of quadratic discriminant analysis (QDA), which resulted in the correct classification of all samples according to the treatment stage. In addition, it was found that differences in the illumination of the samples can be standardized by converting the RGB data to the YCbCr format and correcting the luminance (Y) component. This correction may unveil changes in the seston features that were previously masked by the illumination variability.

Introduction
Over the last few years, environmental problems related to anthropic activities (both domestic and industrial) have increased significantly in urban centers.1 Such problems have motivated the implementation of programs for monitoring water resources,2 as well as the deployment of policies to minimize potential hazards to the environment and the public health. In this context, one may cite the Brazilian national policy of