DEVELOPMENT OF A WATER QUALITY INDEX WITH A REDUCED NUMBER OF PARAMETERS

ABSTRACT The development of water quality indices (WQIs), duly modified and using a small number of parameters, may be of great economic use. The purpose of this work was to develop a WQI with a reduced number of parameters (WQIred), in relation to what is used in the Brazilian state of Minas Gerais (WQIIGAM), in the basin of the Doce River. Four different scenarios were analysed, with the absence of the following parameters for the calculation of the WQIred: BOD, E. coli and phosphate; BOD and E. coli; BOD, E. coli and total solids (TS); BOD, E. coli, phosphate and TS. The redistribution of the weight attributed to the eliminated parameters was done according to the following methods: (i) in weighted form, through optimisation of the correlation between the WQIred and the WQIIGAM; (ii) based on the cluster analysis. The best scenario found was that of the WQIred considering only DO, pH, temperature variation, nitrates and turbidity, with the weights being redistributed based on cluster analysis. This scenario maintained satisfactory performance, with a minimum difference being observed between WQIIGAM and WQIred, in terms of management purpose. The WQIred as proposed makes it possible to establish a monitoring control system operating in real time in the Doce river basin, as all the parameters considered can be obtained with the use of multiparameter probes.