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Formação de triclorometano em águas residuais cloradas: risco de contaminação dos recursos hídricos
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Resumo(s)
A desinfeção é uma etapa essencial para garantir o uso da água em segurança. No entanto, a desinfeção por via química pode originar reações secundárias com a matéria orgânica de origem natural, das quais pode resultar a formação de compostos organohalogenados, nomeadamente trihalometanos, que constituem um risco potencial para a saúde humana, uma vez que poderão ser precursores de algumas formas de cancro, e para o ambiente aquático atendendo à sua persistência, toxicidade e bioacumulação. Com o presente trabalho pretendeu-se estudar a cloragem de águas residuais destinadas à reutilização para rega de espaços verdes (e.g., campos de golfe) e avaliar a formação de triclorometano (clorofórmio). Para o efeito, numa primeira fase, foram realizados ensaios de preparação de efluentes artificiais com características semelhantes a águas residuais urbanas e estudada a respetiva carência de cloro. As águas residuais artificiais foram sujeitas a ensaios de cloragem e avaliada a formação de triclorometano ao longo do tempo de reação. Com os resultados obtidos foi desenvolvido um modelo de regressão linear múltipla para a formação de triclorometano em função da dose de cloro utilizada e do tempo de reação. Neste trabalho foi também desenvolvida uma metodologia para a definição de valores limite de emissão para o triclorometano a aplicar na rejeição de águas residuais tratadas no meio hídrico, e na avaliação das técnicas de cloragem associadas à reutilização para rega de espaços verdes (e.g., campos de golfe), tendo em conta as variações sazonais e de modo a não colocar em risco o cumprimento das normas de qualidade ambiental previstas para as águas superficiais. Para otimização dos procedimentos associados à cloragem de águas residuais, destinadas à rejeição no meio hídrico ou à reutilização, foi efetuada uma avaliação de risco através da aplicação de um modelo baseado numa análise multicritério, o qual engloba a avaliação dos recursos hídricos superficiais e subterrâneos e a avaliação das caraterísticas das fontes de perigo relacionadas com o uso e armazenamento de produtos clorados.
The disinfection is a crucial stage in the water treatment to ensure a safe water use. However, the chemical disinfection can lead to secondary reactions with the natural organic matter and subsequent formation of halogenated compounds, such as trihalomethanes, regarded as particularly dangerous to human health, following their potential as cancer precursors, and to the aquatic environment due to their toxicity, persistence and bioaccumulation. The current essay intended to study the chlorination of wastewaters for reuse in green areas irrigation (e.g., golf courses) and evaluate the trichloromethane (chloroform) formation. For this purpose artificial wastewaters with similar characteristics to urban sewage were developed and the corresponding demand for chlorine was studied. The artificial wastewaters were chlorinated and the trichloromethane formation as a time function was studied. According to these results a multiple linear regression model for the trichloromethane formation based on the chlorine dose and time reaction was developed. In the project a methodology to define Emission Limit Values to be applied to the wastewater discharges to water resources and to evaluate chlorination practices related with reuse for green areas irrigation (e.g., golf courses) was also developed, according to season variability and to ensure the compliance of environmental quality standards applicable to surface waters. To improve the disinfection procedures, on the wastewater discharges and reuse, a risk assessment was promoted. For this purpose a multi-criteria based analysis model was used, which involves a screening for environmental risk sources, related with the use and storage of chlorinated products, and the groundwater and surface water characteristics assessment.
The disinfection is a crucial stage in the water treatment to ensure a safe water use. However, the chemical disinfection can lead to secondary reactions with the natural organic matter and subsequent formation of halogenated compounds, such as trihalomethanes, regarded as particularly dangerous to human health, following their potential as cancer precursors, and to the aquatic environment due to their toxicity, persistence and bioaccumulation. The current essay intended to study the chlorination of wastewaters for reuse in green areas irrigation (e.g., golf courses) and evaluate the trichloromethane (chloroform) formation. For this purpose artificial wastewaters with similar characteristics to urban sewage were developed and the corresponding demand for chlorine was studied. The artificial wastewaters were chlorinated and the trichloromethane formation as a time function was studied. According to these results a multiple linear regression model for the trichloromethane formation based on the chlorine dose and time reaction was developed. In the project a methodology to define Emission Limit Values to be applied to the wastewater discharges to water resources and to evaluate chlorination practices related with reuse for green areas irrigation (e.g., golf courses) was also developed, according to season variability and to ensure the compliance of environmental quality standards applicable to surface waters. To improve the disinfection procedures, on the wastewater discharges and reuse, a risk assessment was promoted. For this purpose a multi-criteria based analysis model was used, which involves a screening for environmental risk sources, related with the use and storage of chlorinated products, and the groundwater and surface water characteristics assessment.
Descrição
Palavras-chave
Cloragem - Águas residuais Cloragem - Subprodutos de desinfecção Cloragem - Triclorometano Águas residuais - Cloragem - Reutilização Águas residuais - Reutilização - Qualidade da água