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Abstract(s)
Os sistemas de tratamento biológicos convencionais não removem a totalidade dos constituintes presentes nas águas residuais domésticas, sendo frequente a presença nos seus efluentes de residuais (e.g. matéria orgânica solúvel, biodegradável ou refractária, produtos resultantes da actividade microbiológica e compostos inorgânicos solúveis) que podem causar impactes ambientais significativos nas massas hídricas e no solo, nomeadamente nos seus potenciais usos. Quando o meio receptor é sensível à descarga destes constituintes remanescentes ou, a jusante é utilizado para determinados usos, é necessário efectuar a sua remoção, podendo ser utilizados sistemas de tratamento avançados ou de afinação como é o caso dos filtros biológicos de leito imerso. Apesar de existirem vários estudos sobre a aplicabilidade destes sistemas na eliminação de nutrientes, a sua utilização para a remoção de residuais de carbono não tem sido, contudo, avaliada.
Nestes termos, o objectivo principal deste trabalho centrou-se no estudo da biodegradação de residuais de carbono, comuns em efluentes de tratamento secundário de águas residuais urbanas e água bruta de origem superficial, através da utilização de um filtro biológico de leito imerso, tendo, complementarmente, sido estudada a remoção de azoto (amónio e formas oxidadas de azoto). Realizaram-se ensaios complementares para o estudo das condições hidrodinâmicas no filtro e ensaios para avaliar as condições básicas de operação, tendo em atenção a estabilidade do processo e a evolução da perda de carga no leito ao longo do tempo. Nos ensaios de biodegradação foram utilizados substratos simples (acetato) e complexos (água residual doméstica e água de origem superficial), tendo-se testado diferentes condições de carga (carga orgânica aplicada e razão C/NH4+-N) e de operação (arejamento, ciclo de lavagem e número de passagens pelo leito).
Os resultados permitiram concluir, para a gama de cargas orgânicas (5,2 g C m-3 h-1 a 77,3 g C m-3 h-1) e de azoto amoniacal (0,2 g NH4+-N m-3 h-1 e 38,7 g NH4+-N m-3 h-1) aplicadas, que o filtro utilizado permitia obter remoção carbonada, nitrificação e desnitrificação, a taxas de eliminação satisfatórias. Não se observou, contudo, remoção de qualquer dos compostos para cargas inferiores a 5,2 g C m-3 h-1 e 1,5 g NH4+-N m-3 h-1.
A remoção mais importante, quer de carbono, quer de azoto amoniacal, foi observada no intervalo de cargas orgânicas médias entre 25,7 g C m-3 h-1 e 77,3 g C m-3 h-1, em particular na parte superior do leito (8,0 cm iniciais) onde ocorreu forte dispersão, o oxigénio dissolvido apresentou as concentrações mais elevadas, foram observadas maiores produções de biomassa e uma camada de biofilme mais densa. A adopção de uma segunda passagem pelo leito contribuiu para o aumento da remoção de ambos os compostos, apenas para cargas orgânicas médias superiores a 25,7 g C m-3 h-1.
Os resultados permitiram, ainda, constatar que a remoção de formas oxidadas de azoto, essencialmente constituídas por nitratos, independentemente do tipo de substrato e das condições de carga e de operação utilizadas, ocorreu, principalmente, por desnitrificação.
Nestes termos, a utilização de filtros biológicos de leito imerso para a remoção de residuais de carbono, poderá constituir alternativa económica e tecnicamente vantajosa tendo em vista, quer a redução de impactes ambientais de descargas em meios hídricos e no solo, quer a produção de efluentes com potencial de reutilização, podendo, complementarmente, ser obtida a remoção de azoto.
Biological treatment systems do not achieve total removal of the wastewater constituents being normal the presence in the effluent of a residual part (mainly slowly biodegradable substrates and soluble microbial products), which do not ensure compliance with the regulations and environmental policies, constituting a cause of concern as they can reduce biodiversity and produce impacts on potential water and soil uses. When discharge points are sensitive or the water is used downstream, it becomes necessary to remove this residual loading. This can be achieved by integrating an advanced treatment unit such as a biological filter. Biological filtration through submerged packed bed is a technology recently looked as useful for wastewater treatment and reuse systems, especially for nutrient removal. However, its use for carbon residuals removal has not been found in the consulted literature. Therefore, the main objective of this work was to study the carbon residual removal in a biological submerged packed bed. An interpretation concerning the removal of nitrogen (both as ammonia and oxidized forms) was also done. A series of complementary assays has been carried out in order to enable a better understanding of the hydrodynamic characteristics of the filter as well as the basic operation procedures to allow steady-state conditions. Biodegradation assays have been performed with simple (acetate) and complex (secondary treated wastewater and raw water) substrates for different loading (C/NH4 +-N ratio and organic loading) and operation conditions (air supply, filter washing and number of treatment stages). The results showed that, for the applied carbon (5,2 g C m-3 h-1 to 77,3 g C m-3 h-1) and ammonia (0,2 g NH4 +-N m-3 h-1 to 38,7 g NH4 +-N m-3 h-1) loadings, the filter has achieved good performance in terms of carbon removal, nitrification and denitrification. However, for organic loadings below 5,2 g C m-3 h-1 there was no significant removal of both compounds. The removal of both compounds was more important for organic loadings between 25,7 g C m-3 h-1 and 77,3 g C m-3 h-1 , especially in the upper 8,0 cm of the filter, where a considerable amount of dispersion and the higher dissolved oxygen concentrations were observed. In this part of the filter was also noted a significant biomass production as well as more dense biofilme layer. The adoption of a simulated second stage of treatment has improved the removal rate of both compounds only for organic loadings above 25,7 g C m- 3 h-1. Independently of loading and operation conditions the removal of oxidized forms of nitrogen (mainly nitrate) has been achieved through denitrification. In these terms, the use of biological submerged packed beds for carbon residuals removal seems to be an economical and technical promising solution in order to reduce the potential environmental impact of discharges on water and soil as well as to produce final effluents for reuse. Additionally, reduction of the nitrogen loading can also be achieved.
Biological treatment systems do not achieve total removal of the wastewater constituents being normal the presence in the effluent of a residual part (mainly slowly biodegradable substrates and soluble microbial products), which do not ensure compliance with the regulations and environmental policies, constituting a cause of concern as they can reduce biodiversity and produce impacts on potential water and soil uses. When discharge points are sensitive or the water is used downstream, it becomes necessary to remove this residual loading. This can be achieved by integrating an advanced treatment unit such as a biological filter. Biological filtration through submerged packed bed is a technology recently looked as useful for wastewater treatment and reuse systems, especially for nutrient removal. However, its use for carbon residuals removal has not been found in the consulted literature. Therefore, the main objective of this work was to study the carbon residual removal in a biological submerged packed bed. An interpretation concerning the removal of nitrogen (both as ammonia and oxidized forms) was also done. A series of complementary assays has been carried out in order to enable a better understanding of the hydrodynamic characteristics of the filter as well as the basic operation procedures to allow steady-state conditions. Biodegradation assays have been performed with simple (acetate) and complex (secondary treated wastewater and raw water) substrates for different loading (C/NH4 +-N ratio and organic loading) and operation conditions (air supply, filter washing and number of treatment stages). The results showed that, for the applied carbon (5,2 g C m-3 h-1 to 77,3 g C m-3 h-1) and ammonia (0,2 g NH4 +-N m-3 h-1 to 38,7 g NH4 +-N m-3 h-1) loadings, the filter has achieved good performance in terms of carbon removal, nitrification and denitrification. However, for organic loadings below 5,2 g C m-3 h-1 there was no significant removal of both compounds. The removal of both compounds was more important for organic loadings between 25,7 g C m-3 h-1 and 77,3 g C m-3 h-1 , especially in the upper 8,0 cm of the filter, where a considerable amount of dispersion and the higher dissolved oxygen concentrations were observed. In this part of the filter was also noted a significant biomass production as well as more dense biofilme layer. The adoption of a simulated second stage of treatment has improved the removal rate of both compounds only for organic loadings above 25,7 g C m- 3 h-1. Independently of loading and operation conditions the removal of oxidized forms of nitrogen (mainly nitrate) has been achieved through denitrification. In these terms, the use of biological submerged packed beds for carbon residuals removal seems to be an economical and technical promising solution in order to reduce the potential environmental impact of discharges on water and soil as well as to produce final effluents for reuse. Additionally, reduction of the nitrogen loading can also be achieved.
Description
Keywords
Biofiltro Remoção de residuais Remoção de azoto Reuso Filtro biológico Biofilme