Information entropy for evaluation of wastewater composition

Abstract

The composition of wastewaters collected during one year was evaluated based on the Shannon information entropy. Eleven physico-chemical parameters, biochemical oxygen demand (BOD), chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN), total suspended solids (TSS), total dissolved salts (TDS), pH, ammonium, phosphate, cyanide and phenol, were determined for their characterization. Entropy of the parameters calculated by means of their histograms decreased in the order: phosphate > ammonium > TDS > TN > pH > BOD > COD > TSS > TP > phenol > cyanide. Entropy weights of the parameters were calculated for the evaluation of wastewater composition by means of the entropy weighted index (EWI) defined according to the simple additive weighting (SAW) model. The EWI values were statistically processed by us to observe temporal wastewater composition changes and were verified by means of the principal component weighted index (PCWI). The EWI values were statistically analyzed by univariate statistics. The outlaying samples were also confirmed by multivariate analysis. The entropy-based approach allowed us to simply evaluate wastewater composition by means of one index instead of several parameters. The main advantage of EWI is the simple histogram-based calculation of entropy with no need of the normal distribution of the used parameters.