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 26thAugust 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 werethen 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 correctclassiﬁcation 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.
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 ofwater resources.3 Within this scope, one of the main problems consists of efﬂuent discharges from wastewater treatment stations. Environmental regulations usually dictate criteria for the selection of the discharge site and the level of treatment to ensure that the resulting impact is kept at acceptable levels.3,4 However, unauthorized connections to industrial or domestic wastewater sources maycompromise the efﬁcacy of the treatment process, due to the destruction of bacterial groups involved in the decomposition of organic matter.
a Instituto Federal de Educaca Ci^ncia e Tecnologia da Paraba (IFPB), ¸ ˜o, e ı 58.015-430 Joa Pessoa, Paraba, Brazil ˜o ı b Universidade Federal de Gois, Instituto de Informtica, 74001-970 a a Goi^nia, Gois, Brazil a a c Pontifcia Universidade Catlicade Gois, Departamento de Computaca ı o a ¸ ˜o, 74605-010 Goi^nia, Gois, Brazil a a d Universidade Federal Rural de Pernambuco, Unidade Acad^mica de Serra e Talhada (UAST), 56900-000 S Talhada, Pernambuco, Brazil e Universidade Federal da Paraba, Centro de Ci^ncias Exatas e da ı e Natureza, Departamento de Qumica, Caixa Postal 5093, 58051-970 ı Joa Pessoa, Paraba, Brazil. E-mail:firstname.lastname@example.org ˜o ı f Instituto Tecnolgico de Aeronutica, Divisa de Engenharia Eletr^nica, o a ˜o o 12228-900 Sa Jos dos Campos, SP, Brazil ˜o e
Several authors5–8 have published studies on the performance assessment of treatment processes, as well as the veriﬁcation of compliance with discharge standards. However, the analytical methods usually employed for this purpose are laborious andtime-consuming, which may not allow appropriate corrective actions to be taken in a timely manner.9 In this sense, the development of fast methods for screening analysis2,10–16 would be of value to detect relevant alterations in the efﬂuent properties at different stages of the treatment process. For this purpose, the use of digital images may be an interesting approach. Pagola et al.17 developed a low...
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