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Estudo do decaimento de cloro no tratamento e distribuição de águas
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Abstract(s)
A água é distribuída às populações através de uma rede de abastecimento, após ser tratada numa estação de tratamento. Ao longo da rede, é importante que o cloro se mantenha em concentrações adequadas para a saúde pública. Assim, é relevante estudar o decaimento do cloro residual livre nas redes de distribuição, para verificar se a concentração se encontra dentro do intervalo recomendado. Este trabalho teve como objetivo determinar o decaimento do cloro residual livre, num caso de estudo real, nomeadamente, na rede de distribuição de água do piso 2 do edifício C do ISEL. Para alcançar este objetivo, foram recolhidas 56 amostras de água em torneiras de baixo e elevado consumo, com e sem purga (fornecida e estagnada), medindo-se as concentrações de cloro residual livre, o pH e a temperatura. Posteriormente, foi construído no EPANET um modelo de simulação hidráulica e de qualidade da água da rede em estudo. A calibração baseou-se em determinações analíticas dos parâmetros hidráulicos e nas medições de cloro. As medições de cloro indicaram que, nos pontos de baixo consumo, 21% amostras com purga e 43% sem purga estavam abaixo do valor recomendado, possivelmente por estagnação, sugerindo contaminação microbiológica. Nos pontos de elevado consumo, nenhuma amostra ficou abaixo do recomendado; porém, 86% amostras com purga e 43% sem purga excederam o recomendo, indicando possível formação de subprodutos de desinfeção prejudiciais à saúde humana. Foram realizadas 34 simulações com 6 cenários (A1 a C2), variando consumos nodais, alturas piezométricas e concentrações de cloro no reservatório. Após calibração hidráulicas, simulou-se a qualidade da água quanto ao cloro residual livre, observando-se excedências do recomendado em períodos de maior e menor consumo. Conclui-se que, para manter as concentrações de cloro dentro do intervalo recomendado, concentrações de cloro próximo à entrada do ISEL devem ser mantidas entre 0,30 e 0,60 mg/L.
Abstract Water is distributed to populations through a supply network after being treated at a water treatment plant. Along the network, it is important to maintain chlorine concentrations at levels that are safe for public health. Therefore, studying the decay of free residual chlorine in distribution networks is crucial to ensure that concentrations remain within the recommended range. This study aimed to determine the decay of free residual chlorine in a real case study, specifically in the water distribution network on the second floor of building C at ISEL. To achieve this, 56 water samples were collected from low- and high-consumption faucets, both with and without flushing (supplied and stagnant water), measuring the concentrations of free residual chlorine, pH, and temperature. Subsequently, a hydraulic and water quality simulation model of the network was developed using EPANET. The calibration was based on estimates of hydraulic parameters and chlorine measurements. Chlorine measurements revealed that, at low-consumption points, 21% of the samples with flushing and 43% without flushing fell below the recommended threshold, likely due to stagnation, which may indicate microbiological contamination. In contrast, at high-consumption points, none of the samples were below the recommended value; however, 86% of the samples with flushing and 43% without flushing exceeded the recommended limit, suggesting the potential formation of disinfection by-products that could pose risks to human health. A total of 34 simulations were carried out with 6 scenarios (A1 to C2), varying nodal consumption, piezometric heights, and chlorine concentrations in the reservoir. After hydraulic calibration, water quality was simulated regarding free residual chlorine, observing exceedances of the recommended value during periods of both high and low consumption. It is concluded that, to maintain chlorine concentrations within the recommended range, chlorine concentrations near the ISEL entrance should be kept between 0.30 and 0.60 mg/L.
Abstract Water is distributed to populations through a supply network after being treated at a water treatment plant. Along the network, it is important to maintain chlorine concentrations at levels that are safe for public health. Therefore, studying the decay of free residual chlorine in distribution networks is crucial to ensure that concentrations remain within the recommended range. This study aimed to determine the decay of free residual chlorine in a real case study, specifically in the water distribution network on the second floor of building C at ISEL. To achieve this, 56 water samples were collected from low- and high-consumption faucets, both with and without flushing (supplied and stagnant water), measuring the concentrations of free residual chlorine, pH, and temperature. Subsequently, a hydraulic and water quality simulation model of the network was developed using EPANET. The calibration was based on estimates of hydraulic parameters and chlorine measurements. Chlorine measurements revealed that, at low-consumption points, 21% of the samples with flushing and 43% without flushing fell below the recommended threshold, likely due to stagnation, which may indicate microbiological contamination. In contrast, at high-consumption points, none of the samples were below the recommended value; however, 86% of the samples with flushing and 43% without flushing exceeded the recommended limit, suggesting the potential formation of disinfection by-products that could pose risks to human health. A total of 34 simulations were carried out with 6 scenarios (A1 to C2), varying nodal consumption, piezometric heights, and chlorine concentrations in the reservoir. After hydraulic calibration, water quality was simulated regarding free residual chlorine, observing exceedances of the recommended value during periods of both high and low consumption. It is concluded that, to maintain chlorine concentrations within the recommended range, chlorine concentrations near the ISEL entrance should be kept between 0.30 and 0.60 mg/L.
Description
Trabalho de Projeto para obtenção do grau de Mestre em Engenharia da Qualidade e Ambiente
Keywords
Decaimento de cloro residual livre Modelação Calibração EPANET 2.2. Free residual chlorine decay Modeling Calibration
Citation
FERNANDES, Patrícia Alexandra da Silva – Estudo do decaimento de cloro no tratamento e distribuição de águas. Lisboa: Instituto Superior de Engenharia de Lisboa. 2024. Dissertação de Mestrado.