Evaluation of turbidity removal at the Seminário WTP

A comparative analysis of PAC and aluminum sulfate coagulants

Abstract

Objective - To perform a statistical analysis of the efficiency of the aluminum polychloride (PAC) coagulant used at the Seminário Water Treatment Plant (WTP), located in the municipality of Mariana, Minas Gerais, in comparison with aluminum sulfate (Al₂(SO₄)₃), which was used at the plant until 2020, with a specific focus on turbidity removal. Additionally, the study aims to assess the compliance of recorded treated water turbidity values with the current drinking water standards for this parameter, comparing the performance of the coagulants in meeting regulatory criteria.

Methodology - Treated water turbidity data for both coagulants were obtained from the personnel responsible for the operation of the Seminário WTP. As the records were collected manually, they were digitized for subsequent statistical processing. Statistical analysis was conducted using the Kolmogorov-Smirnov (KS) test to verify data adherence to a normal distribution. Subsequently, the nonparametric Mann-Whitney U test was applied to identify possible statistically significant differences between the medians of the samples associated with the use of PAC and Al₂(SO₄)₃.

Originality/Relevance - There is a scarcity of studies that comparatively evaluate, through statistical methods, the efficiency of these two coagulants based on extensive operational datasets, particularly regarding turbidity reduction. The academic relevance of this study lies in the application of statistical methods to real operational data, expanding knowledge about coagulant performance in practical contexts and providing support for future research in the fields of water treatment and sanitation.

Results - The KS test indicated that the samples do not follow a normal distribution. The Mann-Whitney U test showed that the median turbidity after treatment with PAC is statistically lower than the median turbidity after treatment with Al₂(SO₄)₃, demonstrating the greater efficiency of PAC in turbidity removal. With respect to drinking water standards, the analysis showed that PAC exhibited superior performance, with a higher proportion of compliant results, whereas the use of Al₂(SO₄)₃ resulted in frequent noncompliance and critical values.

Theoretical/Methodological Contributions - The study contributes theoretically by demonstrating, based on empirical data, the greater efficiency of PAC compared to Al₂(SO₄)₃ in reducing water turbidity at a water treatment plant. Methodologically, the work provides a replicable model for the comparative evaluation of coagulants using operational records.

Social and Environmental Contributions - Understanding which of the two coagulants is more effective in removing suspended particles from water, represented by turbidity, can directly influence decision-making regarding their adoption at a WTP and lead to a more refined water treatment process. This contributes to the production of higher-quality drinking water, positively impacting public health and the quality of life of the consuming population.