Avaliação do desempenho de uma estação de tratamento de esgoto por meio de testes de hipótese

Abstract

The stabilization ponds are a domestic and industrial effluent treatment system that has many advantages. They are economical, present good efficiency in removing organic matter and they are easy to operate and maintain. This work aims to evaluate the performance of Industrial Wastewater Treatment Plant (WWTP), located in Araguari – MG. The Industrial WWTP treats domestic and industrial effluent, composed of a facultative pond, a maturation pond, a root pond and a reuse pond. The evaluation was based on the monthly monitoring reports of the effluent, and the following parameters were evaluated: pH, Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), temperature, turbidity, electrical conductivity, oils and grease, sedimentable solids, total suspended solids, E. coli and thermotolerante coliforms. By means of the statistical hypothesis tests, ANOVA, Tukey's Test, Kruskal-Wallis' Test and Mann-Whitney's Test, the comparisons of the mean values of the parameters in the years 2019, 2020 and 2021 and the comparison in the entrances and exist of the treatment were obtained. The results were compared with state and federal legislation (COPAM ND 01/2008 and CONAMA Resolution 430/2011, respectively), and with the Minas Gerais legislation that establishes quality standards for reuse water (CERH ND 65/2020). For reuse water, the pH is within the limit established by the CERH ND 65/2020 and the amount of E. coli is above the permitted limit. The other parameters studied don’t have limit values established by this law. The results of statistical tests were generated in the PAST software, showing that in all years, the temperature, pH, electrical conductivity, total suspended solids and oils and grease were in accordance with the limit established by the legislation. On the other hand, BOD, COD, turbidity, settleable solids, E. coli, and thermotolerant coliforms were above the value allowed by the legislation, in at least one of the years evaluated. In 2019, BOD removal was 50.05% and COD removal was 53.88%. In 2020, BOD removal was 73.56% and COD removal was 74.08%. In 2021, BOD removal was 86.58% and COD removal was 85.41%. The addition of a chemical treatment in the Industrial WWTP is indicated to better disinfect the effluent, and more detail in the monthly monitoring reports to better follow up on the treatment efficiency.