Avaliação da flotação por ar dissolvido no pós-tratamento de águas residuárias de frigorífico avícola

Abstract

he Brazilian poultry slaughtering and processing industry plays a strategic role in the global economy but faces the environmental challenge of managing wastewater with high organic, lipid, and nutrient loads. Inadequate treatment of this wastewater may compromise the quality of water bodies and result in legal sanctions, making operational efficiency a strategic component of competitiveness. The general objective of this study was to analyze the performance of an industrial Wastewater Treatment Plant (WWTP), assessing the impact of implementing a Dissolved Air Flotation (DAF) system as a tertiary polishing step and the efficiency of the operational units throughout the process, with the aim of ensuring environmental compliance and system resilience. The methodology adopted a mixed-methods approach, integrating a Systematic Literature Review (SLR) and a full-scale case study. Performance was assessed from two perspectives: a longitudinal analysis of parameters from 2019 to 2025 to compare the pre- and post-DAF operating regimes, and monitoring of the system’s operational units. The SLR was conducted through the identification and critical analysis of scientific articles published between 2015 and 2025 and indexed in specialized databases, namely Scopus, Web of Science, SciELO, and Google Scholar, to provide a foundation for the state of the art and the use of this technology. For the case study, data were collected from 2019 to 2025 at an industrial Wastewater Treatment Plant (WWTP) located in São Sebastião do Oeste, Minas Gerais, Brazil, to evaluate DAF efficiency, followed by data collection from April 2024 to July 2025 to provide an overview of the process. Some of the parameters analyzed were biochemical oxygen demand (BOD), chemical oxygen demand (COD), total phosphorus, ammoniacal nitrogen, total suspended solids (TSS), and pH. Descriptive statistics and nonparametric inferential tests, namely the Wilcoxon–Mann–Whitney and Kruskal–Wallis tests, were applied at a 5% significance level. The main results demonstrate that the implementation of DAF in 2021 resulted in the stabilization of the final discharge, even under an average flow rate that was 44% higher and exhibited lower hydraulic variability. The average BOD and COD removal efficiencies increased to 97.6% and 97.0%, respectively, with the final BOD reaching a median concentration of 17.7 mg/L. The system removed more than 98% of the residual total suspended solids (TSS) from the aerated lagoons, reducing the final median concentration to 18.0 mg/L. In addition, the total phosphorus removal efficiency increased to 69.5%, demonstrating resilience despite a twofold increase in the influent load concentration during the period. The integrative discussion of the data obtained from the case study and the systematic literature review (SLR) revealed unsatisfactory biological performance between the anaerobic reactor effluent (2LA) and the dissolved air flotation influent (4FT), with partial BOD removal efficiencies remaining between 20% and 26%. This scenario demonstrates that DAF acts as an important barrier by processing raw organic loads that should have been degraded during the preceding biological treatment stages. It is concluded that, although DAF technology is essential for ensuring legal compliance and final effluent quality, in accordance with CONAMA Resolutions No. 357 and No. 430, the system exhibits structural vulnerability. It is imperative to optimize the hydraulic retention time and aeration of the biological lagoons to prevent saturation of the physicochemical treatment unit and ensure the long-term environmental sustainability of the plant.