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OTIMIZAÇÃO DA ETAPA DE FLOTAÇÃO NA ETA DE ALCANTARILHA
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O acesso a água potável é uma questão de máxima importância para a saúde pública e para o desenvolvimento e o bem-estar da sociedade.
O acesso a água potável e a saneamento básico, estão estabelecidos como um dos direitos humanos e esse acesso está associado a múltiplos benefícios desde a melhoria das condições de saúde até à melhoria da qualidade de vida e ao impulsionar da economia e do desenvolvimento dos países contribuindo de forma significativa para a diminuição da pobreza.
Em Portugal o setor de abastecimento público de água para consumo humano tem evoluindo significativamente, no entanto ainda existem desafios para serem encarados, nomeadamente no que toca à operação das instalações e ao desenvolvimento e aperfeiçoamento das tecnologias utilizadas.
Existem vários tipos de tratamento de separação sólido-líquido. A flotação é um processo de tratamento de separação sólido-líquido que, em comparação com processos mais tradicionais, como é o caso da decantação, apresenta algumas vantagens, particularmente no que diz respeito à área requerida pelos órgãos, aos custos dos reagentes que para esta operação unitária são inferiores aos convencionais e à maior eficiência de remoção de partículas finas.
Existem vários tipos de operação de flotação, estes geralmente diferem entre si na forma como o ar está presente na água, isto é, na forma de produção de bolhas. A flotação por ar dissolvido (FAD) é o processo presente na ETA de Alcantarilha e assenta na compressão de ar com água sendo posteriormente libertado no flotador, à pressão atmosférica.
Devido à sua sensibilidade com variações da qualidade da água afluente, nomeadamente, à carga de partículas presentes na água, a otimização destes sistemas é alvo de diversos estudos, sendo bastante comum a referência à importância do desempenho do pré-tratamento que antecede a flotação. Assim, procedeu-se ao estudo da otimização do flotador da ETA de Alcantarilha, inicialmente através de uma análise à qualidade da água bruta que chega à ETA, revelando uma água de qualidade, com características que não interagem negativamente com a flotação.
Estudaram-se também as condições de operação praticadas na ETA durante um período pré-estabelecido e foram realizados quatro ensaios de flotest, método que visa a identificação da melhor dose de reagentes, de modo a comparar as doses de reagentes que têm sido utilizadas com a dose ótima a que se chegou nos ensaios.
Posto isto, chegou-se à conclusão de que a dose que obteve melhores resultados foi 15 e 0,25 ppm de coagulante e floculante, respetivamente, mas que, considerando os resultados dos ensaios realizados, permite pensar que existe, ainda, margem para redução de ambas as doses mantendo uma boa "performance".
Por fim, os resultados do balanço de massa de alumínio concluíram que uma redução na dosagem de coagulante seria benéfica, demonstrando que as etapas de coagulação têm um enorme contributo para a circulação de alumínio na ETA.
Access to drinking water is considered to be a matter of most importance for public health and for the development of society at local, regional and national level. There are many benefits of access to clean water and basic sanitation, from a reduction in harmful health effects and associated treatment costs that outweigh the costs of interventions, even by boosting a country's economy and helping to reduce poverty. In Portugal the public water supply sector for human consumption has evolved significantly, although there is still scope for progression, particularly with regard to technical operation. There are several types of solid-liquid separation treatment. Flotation is a process of solid-liquid separation treatment which, compared to more traditional processes, such as decanting, has some advantages, particularly with regard to the space occupied by the organs, the costs of acquiring lower reagents and the removal of fine particles more efficiently. There are several types of flotation, these usually differ from each other in the way air is present in water, that is, in the form of bubble production. Dissolved air flotation (DAF) is the process present in Alcantarilha Water Treatment Plant and is based on the compression of air with water being released later in the flotator at atmospheric pressure. Due to its sensitivity to variations in the quality of the affluent water, namely the load of particles presents in the water, the optimization of these systems is the subject of several studies, being quite common the reference to the importance of the performance of pre-treatment that precedes flotation. Thus, the optimization of the Alcantarilha Water Treatment Plant´s flotator was carried out, through, initially, an analysis of the quality of raw water that reaches the Water Treatment Plant, revealing a quality water with characteristics that do not impair flotation. The operating conditions practiced in the Water Treatment Plant during a pre-established period were also studied and two flotest trials were performed, a method aimed at identifying the best dose of reagents, in order to compare the doses of reagents that have been used with the optimal dose reached in the trials. Having said that, it was concluded that the dose that obtained the best results was 15 and 0.25 ppm of coagulant and flocculant, respectively, but that, due to the trials, there may be a margin of reduction of both doses maintaining good results. Finally, the results of the aluminum mass balance concluded that a reduction in coagulant dosage would be beneficial, demonstrating that coagulation steps have a huge contribution to aluminum circulation in the Water Treatment Plant.
Access to drinking water is considered to be a matter of most importance for public health and for the development of society at local, regional and national level. There are many benefits of access to clean water and basic sanitation, from a reduction in harmful health effects and associated treatment costs that outweigh the costs of interventions, even by boosting a country's economy and helping to reduce poverty. In Portugal the public water supply sector for human consumption has evolved significantly, although there is still scope for progression, particularly with regard to technical operation. There are several types of solid-liquid separation treatment. Flotation is a process of solid-liquid separation treatment which, compared to more traditional processes, such as decanting, has some advantages, particularly with regard to the space occupied by the organs, the costs of acquiring lower reagents and the removal of fine particles more efficiently. There are several types of flotation, these usually differ from each other in the way air is present in water, that is, in the form of bubble production. Dissolved air flotation (DAF) is the process present in Alcantarilha Water Treatment Plant and is based on the compression of air with water being released later in the flotator at atmospheric pressure. Due to its sensitivity to variations in the quality of the affluent water, namely the load of particles presents in the water, the optimization of these systems is the subject of several studies, being quite common the reference to the importance of the performance of pre-treatment that precedes flotation. Thus, the optimization of the Alcantarilha Water Treatment Plant´s flotator was carried out, through, initially, an analysis of the quality of raw water that reaches the Water Treatment Plant, revealing a quality water with characteristics that do not impair flotation. The operating conditions practiced in the Water Treatment Plant during a pre-established period were also studied and two flotest trials were performed, a method aimed at identifying the best dose of reagents, in order to compare the doses of reagents that have been used with the optimal dose reached in the trials. Having said that, it was concluded that the dose that obtained the best results was 15 and 0.25 ppm of coagulant and flocculant, respectively, but that, due to the trials, there may be a margin of reduction of both doses maintaining good results. Finally, the results of the aluminum mass balance concluded that a reduction in coagulant dosage would be beneficial, demonstrating that coagulation steps have a huge contribution to aluminum circulation in the Water Treatment Plant.
Descrição
Palavras-chave
Abastecimento de água Tratamento de água Flotação Flotação por ar dissolvido Qualidade da água Flotest