Potencial de reúso de efluentes tratados em Caicó/RN

Abstract

The scarcity of water has driven the search for new technologies to sustain industrial, agricultural, and urban development. In this context, reclaimed water from wastewater treatment plants (WWTPs) is increasingly considered a viable source for various applications, provided it meets quality standards to avoid risks to human health. In the absence of federal legislation, some states and municipalities have established their own regulations on the subject. One such example is Municipal Law No. 4,603/2013 in Caicó, RN, which defines criteria and standards for agricultural, urban, and aquaculture uses. This study aims to assess the feasibility of reusing treated effluents from three WWTPs in Caicó (Walfredo Gurgel, Vila do Príncipe, and Castelo Branco). The evaluation is based on average values obtained from physicochemical and biological analyses of effluents conducted between January 2022 and May 2024. These results were compared against the limits established by local legislation for each parameter. Demand estimates for effluent reuse considered applications such as aquaculture, agricultural irrigation, vehicle washing, landscape irrigation, and street cleaning. The latter two were quantified using measurements derived from georeferenced images. Vehicle washing demands were estimated based on data from DETRAN-RN, while volumes for agricultural irrigation and aquaculture were derived from allocations issued by ANA and IGARN. Findings reveal that treated effluents from the WWTPs have potential for reuse; however, parameters such as thermotolerant coliforms, BOD and total suspended solids (TSS) exceeded permissible limits set by the law. Specifically, free ammonia levels were above the legal threshold at Castelo Branco and Walfredo Gurgel WWTPs, while the latter also exhibited pH levels inconsistent with regulations for landscape irrigation and agricultural production. Consequently, enabling effluent reuse requires modifications to WWTP design parameters and/or the adoption of polishing mechanisms such as coagulation, filtration, and disinfection. Upon implementing such measures, treated effluents could meet a portion of the estimated demands, including aquaculture activities, washing official municipal vehicles, irrigating major city plazas, and cleaning streets where weekly markets are held. However, agricultural production, which demands higher volumes than the WWTPs can provide, remains only partially addressed.