Qualidade da água em diferentes fases operacionais unitárias da Estação de Tratamento de Água de Macapá (ETAM)

Abstract

The objective of the present research was to statistically test the variation of water quality parameters based on indicators of unit operational stages of the Macapá Water Treatment Plant (ETAM)/Amapá-Brasil. The methodology consisted of the following procedures: a) analysis of available time series of water quality parameters (Cl, pH, Turbidity and Apparent Color) during the months of July and August 2016, 2017 and 2019; b) monitoring and verification of water quality parameters (Cl), pH, Turbidity and Apparent Color, including Total Coliforms and E. coli (2021) to test their compliance with legislation and, when possible, with historical series of years previous ones, analyzing the variations of the parameters after the expansion of new operational units of ETAM; c) statistically test the influence of factors and independent variables of water quality (pH, Turbidity, Apparent Color, Total Coliforms and E. coli) and operational factors (ETA 1, 2 and 23; Time of day; Day of month; Month ; Year; Operational Stage of Collection, Flocculation, Decantation, Filtration, Disinfection) on Cl concentration (Kruskal-Wallis/single and multiple regressions, α<0.05). Results showed that Cl concentration varied significantly with all parameters and factors (except “Month” of Year) (p<0.05). Multiple regression analyzes indicated that the concentration of Cl was significantly correlated with the variables Day, Year and Apparent Color of the series (Raj 2 (GL=2107, F = 340.1) = 0.33, p<0.001), with the exception of "Month" variable. In the analysis of the 2021 series, there was also no significant variation of Cl with Total Coliforms and E. coli, this result being paradoxically opposite to the historical series (2016, 2017 and 2019). And in relation to the application of coagulants and polymers in jar tests, operational inefficiency (dosages) was observed, also generating a probable lack of control of these inputs, reducing the operational efficiency of ETAM. We concluded that the variation of water quality parameters (Cl, pH, Apparent Color, and Turbidity) of the historical series was dependent on operational factors (ETA, Stage, Hour, Day, Month and Year). Neverdeless, the hypothesis of improved water quality after the expansion of new units 2 and 23 was rejected (Kruskal-Wallis test, p<0.01), suggesting that the modernization of the operating system did not significantly impact the improvement of treatment water efficiency. Because the quality of the treated water is not meeting the standards established by the legislation (Ordinance GM/MS No. 888, of May/4/2021) or that ETA 23 was more efficient than the two oldest ones regarding disinfection by Cl. On the contrary, efficiency depends on the correct dosage of chemicals throughout the unit operations. This hypothesis was confirmed with the “Jar Test” analysis, which indicated optimal coagulation pH as an operationally determining environmental and economic aspect.