Avaliação do potencial de produção de água para reúso em estação de tratamento de águas residuárias de pequeno porte

Abstract

Water reuse emerges as a sustainable and strategic solution in the face of increasing water-stress events. In Brazil, although this practice remains underexplored, several sanitation utilities have adopted the principles of circular economy, progressively adjusting their processes to enable the valorization of by-products generated in wastewater treatment plants (WWTPs). In 2020, the State Water Resources Council of Minas Gerais (CERH-MG) issued Normative Resolution No. 65, establishing criteria and quality standards for non-potable water reuse in four modalities Urban, Environmental, Agricultural, and Industrial thus providing a regulatory stimulus for the implementation of this practice within the state. However, few applied studies have assessed its actual feasibility in small-scale plants. The present study aimed to evaluate the potential for non-potable water reuse in a small-scale WWTP. The case study was the Pirajuba WWTP, a secondary-level treatment facility comprising upflow anaerobic sludge blanket (UASB) reactors followed by overland flow application, a treatment configuration characteristic of low-population-density municipalities. The objective was to validate reuse potential to meet the non-potable demand of a municipal tree nursery and an ecological park. The methodology included the characterization of the study area and treatment units, along with the quantitative and qualitative assessment of both user demand and treated effluent, considering the environmental reuse quality standards defined by DN 65 (CERH-MG, 2020). Effluent characterization revealed the need for operational adjustments to ensure compliance with the intended reuse category. Accordingly, an investigative study was conducted that led to the modification of the overland operation regime, shifting from parallel to in-series configuration. The in-series operation fulfilled environmental reuse requirements, presenting a median pH of 7.9, viable helminth eggs < 1 egg·L⁻¹, and a median Escherichia coli reduction of 1.69 log (97.8% removal efficiency); the final median concentration of 6.8 × 10³ remained far below the maximum permissible limit of 1 × 10⁶, as stipulated by DN CERH-MG No. 65/2020.It is concluded that the in-series operation of overland flow application proved to be an effective strategy for enhancing treated effluent quality, validating the proposed non-potable reuse in the environmental modality and reinforcing the potential of small-scale WWTPs as viable producers of reuse water.