Evaluation of biological wastewater treatment process using Mahalanobis distances in original and principal component space: a case study

Abstract

The evaluation of wastewaters treated by biological wastewater treatment plant was performed using multivariate analysis. The samples taken during 1 year were characterized by the Mahalanobis distances (MDs) calculated from 11 original parameters and 4 principal components extracted by principal component analysis. The principal components were interpreted using Ward's hierarchical clustering analysis and factor analysis. Statistical processing of the samples by means of the MDs calculated in the original and PC space was found to be complementary. Since MDs were not normally distributed, the statistical analysis of their log-transformed values (logMDs) was preferred to common Hotelling's or Chi-squared statistics of MD2 ones. The outliers were confirmed by Ward's method and by inspection of their chemical composition. In contrast to complexity and different magnitudes of the original wastewater parameters, the logMD charts provided a simple and effective tool for the evaluation of biological wastewater treatment process.