Evaluating the surface Water quality index fuzzy and its influence on water treatment

Abstract

The RWQI (Raw Water Quality Index) was developed in compliance with deterministic models, in order to assess the treatability of natural waters for human consumption by means of conventional process, basing on the similar procedure of the well-known Water Quality Index developed by the National Sanitation Foundation (WQINSF). The RWQI, however, seemed to require further adjustments regarding mainly rating criteria. In order to find a non-deterministic model that would allow handling uncertainties, the non-linearity of the parameters and the knowledge of the specialists, the Fuzzy Logic was used in new approach to the RWQI. In this context, the new index (named Raw Water Quality Index Fuzzy - RWQIF) was applied to data set of 24 water sources in Brazil evaluating the correlations with the RWQI, the WQICETESB, treated water turbidity and coagulant dose. The inverse correlation between the RWQIF with coagulant dose and treated water turbidity was obtained. However, the low intensity of these correlations indicated that there are other intervening factors in this relation. Finally, this research points out the RWQIF as a suitable support decision-making tool that allows managers to prioritize watershed protection actions in short, medium and long-term, aiming at minimizing the water treatment costs and improving the treated water quality.