Tratamento de água de abastecimento do meio rural por coagulação orgânica e dupla filtração em areia e carvão ativado granular

Abstract

Drinking water is a fundamental resource for ensuring the quality of human life, however, safe access has become a challenge, especially due to the increasing exposure to sources of pollution from inadequate discharge of industrial waste, agricultural activities and sewage, as well as the frequently reported periods of scarcity. In this sense, the investigation of new technologies and improvement of already consolidated technologies in water treatment becomes a viable and fundamental alternative to guarantee safe access to drinking water. This research presents the investigation of a new treatment configuration, the Continuous Fixed Bed Reactor (CFBR), organic post-coagulation and final disinfection in the treatment of surface water of a small rural community in the interior of Rio Grande do Sul. The research was divided into two stages: the first contemplated the pre-treatment stage, where the clarification of raw surface water was carried out with the use of an organic coagulant, the second and main stage contemplated the treatment through the CFBR. The first stage investigated the clarification of raw surface water using an organic coagulant. For this purpose, a 2³ full factorial design was employed. The maximum optimization of the independent variables coagulant dosage, agitation speed, and contact time was considered, based on the removal of the dependent variables apparent color and turbidity. In the second stage, rapid filtration was used in a double-layer granular filter in the CFBR, with layers composed of quartz sand (0.25 m) and granular activated carbon (GAC) (0.45 m) in downward flow, with final disinfection coupled to the CFBR. In this stage, the efficiency was based on meeting the potability parameters described in MS Ordinances Nº 5/2017 and Nº 888/2021, with the physical-chemical parameters being monitored: apparent color, turbidity, pH, electrical conductivity, alkalinity, and free chlorine, and microbiological parameters: total coliforms and Escherichia coli. The monitoring of the hydraulic parameters pressure drop and surface application rate (SAR) was also considered. The clarification results indicated the removal of approximately 52% of apparent color and 47% of turbidity, with an optimal coagulant dosage of 0.83 mL L-1, agitation of 245 RPM and 10 minutes of contact time, providing a favorable condition for subsequent application of the treatment in the CFBR. The results of the analysis of the physicalchemical parameters of the CFBR were subjected to statistical analysis to determine the variation between the clarified water entering the treatment and the water treated by the complete cycle, where a significant difference (p < 0.05) was observed for: free chlorine, pH, electrical conductivity, apparent color and turbidity. Furthermore, the treatment in the CFBR owes its efficiency guaranteed by meeting the potability parameters at the end of the treatment. The CFBRoperated under conditions up to the consumption of eleven bed volumes (0.03283 m³). Under these conditions, a maximum surface application rate of 165.09 m³m-2day-1 was applied, reaching a maximum head loss of 99 cm at the end of the operation. The treatment configuration investigated in this research indicated promising results for the potabilization of surface water intended for public supply, being an alternative to fill the gap of the fragility of water treatment systems in rural areas.