Different protozoa and metazoa populations develop in the activated sludge wastewater treatment processes and are highly dependent on the operating conditions. In the current work the protozoa and metazoa groups and species most frequent in wastewater treatment plants were studied, mainly the flagellate, sarcodine, and ciliate protozoa as well as the rotifer, gastrotrichia, and oligotrichia metazoa.The work is centered on the survey of the wastewater treatment plant conditions by protozoa and metazoa population using image analysis, discriminant analysis (DA), and neural networks (NNs) techniques, and its main objective was set on the evaluation of the importance of raw data pre-processing techniques in the final results. The main pre-processing techniques herein studiedwere the raw parameters reduction set by a joint cross-correlation and decision trees (DTs) procedure and two data normalization techniques: logarithmic normalization and standard deviation normalization.Regarding the parameters reduction methodology, the use of a joint DTs and correlation analysis (CA) procedure resulted in 28 and 30% reductions in terms of the initial parameters set for the stalked and non-stalked microorganisms, respectively. Consequently, the use of the reducedparameters set has proven to be a suitable starting point for both the DA and NNs methodologies, although for the DA an initial logarithmic normalization step is advisable. For the NNs analysis a standard deviation normalization procedure could be considered for the non-stalked microorganismsregarding the operating parameters assessment.
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