STATISTICAL CONTROL OF THE PROCESS APPLIED TO THE MONITORING OF THE WATER QUALITY INDEX

ABSTRACT Analyzing the physical-chemical and biological characteristics allows the evaluation of the water quality of a water body. Thus, the objective of this study was to determine the water quality index of the Passaúna and Piraquara rivers, as well as to apply statistical quality control methodologies to evaluate the data resulting from the monitoring of water quality. Therefore, a database with physico-chemical and microbiological parameters of the Passaúna and Piraquara rivers, a watershed of the Iguaçu River, belonging to the cities of Araucária and Piraquara, respectively Paraná, Brazil, was used to carry out the research. The water quality index was determined with the time series and, subsequently, these data were submitted to the statistical control of the process, with the control charts of individual Shewhart, EWMA and CUSUM, in addition to the development of the process capacity index. The WQI detected that the rivers remained in average quality until the year 2000, however, from that year it was possible to see a decreasing trend in the water quality of the evaluated rivers. The control charts of Shewhart, EWMA, CUSUM and the process capability index were able to identify the decreasing trend in water quality, demonstrating that they are fast and efficient techniques for the evaluation of water quality control.