Viabilidade do reúso de águas cinzas para fins não potáveis em residências unifamiliares a luz dos parâmetros técnicos e requisitos legais no Brasil

Abstract

The availability of water in different regions of the planet, and especially in Brazil, has suffered from prolonged droughts and rotations in the supply of water for human consumption, as well as from the degradation of the hydrographic basin of water sources. The disproportionate distribution of urban water in locations further away from large centers and upscale neighborhoods, as they limit access to drinking water to neighborhoods. This work aims to evaluate the feasibility of reusing gray water generated in a single-family residence for non-potable domestic uses, especially in flushing toilets. The methodology consists in analyzing the technical requirements and legal parameters existing in Brazil, characterizing the potable and non-potable demands for water in homes. The development of the gray water treatment system for reuse in the sanitary discharge was not directly linked to the hydrosanitary system of the urban housing due to existing limiting issues, however the calculations and results achieved were considered as being for the complete cycle of the project, with a focus on reducing the consumption of potable water provided by traditional sources and the generation of sewage. The results achieved in the quality of the gray water coming from the washing machine with the treatment system employed are presented as an alternative for the reuse of water for non-potable purposes, reaching 0.79 mg/L of average residual chlorine, 33.33% of turbidity below the standardized maximum limit, average pH 7.0, total coliforms with 66.67% and thermotolerant coliforms with 88.89% with absence of these microbiological parameters in treated reuse water. With daily consumption 30 liters per person and an annual total 32.96 m³, by all residents, of potable water flushed in the sanitary basin, an annual generation of gray water through the washing machine 12.46 m³ and a total consumption 67.91 m³ of drinking water, there was a total saving 18.34% with the reuse of gray water in 13 months. The system had a payback time of 13 years and 6 months due to the intermittent supply of water in the locality, however the system was viable in a scenario of continuous water supply and a larger scale of consumption of potable water in buildings with greater number of people as housing developments, in addition to guaranteeing the maintenance of springs, groundwater and recovery of degraded green areas with the use of the sludge generated by domestic sanitary sewage.