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Inibição de Daphnias spp. em Estações de Tratamento de Água Residual utilizando um Sistema de Lamas Ativadas
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Advisor(s)
Abstract(s)
A gestão sustentável dos recursos hídricos depende do bom funcionamento das estações de tratamento de águas residuais. De forma a atingirem os limites impostos por lei, em Portugal, regidos pelo Decreto Lei 152/97, de 19 de junho, publicado no Diário da República nº139/1997, as ETAR têm que garantir que diversos parâmetros no descarte de águas residuais tratadas, como a Carência Bioquímica de Oxigénio (CBO), a Carência Química de Oxigénio (CQO) e os sólidos em suspensão (SS) estão abaixo dos valores limite de emissão. No entanto, há ocorrências que comprometem o funcionamento do sistema de tratamento de águas residuais e consequentemente a qualidade do efluente final. No caso do presente trabalho, houve a ocorrência de um microcrustâceo nos decantadores secundários da ETAR de Fátima, que devido á sua mobilidade e grande propagação, comprometeu não só a qualidade do efluente tratado, como também dos processos a jusante do decantador. Dessa forma, pretendeu-se estudar formas de inibir a presença destes organismos no decantador. Para o desenvolvimento do trabalho instalou-se um reator biológico piloto, com o objetivo de replicar o meio de desenvolvimento das Daphnia spp. Que foi monitorizado em termos de diversos parâmetros imediatos (pH, oxigénio dissolvido, potencial oxidação-redução, temperatura, condutividade e sólidos totais dissolvidos) e parâmetros analíticos (CBO, CQO, sólidos totais e em suspensão, azoto total kjeldahl e fósforo). Após a estabilização do reator procedeu-se a ensaios de toxicidade utilizando o hipoclorito de sódio como agente tóxico nos dafniídeos, em que se utilizaram diferentes concentrações (0,76 mg/L, 1,22 mg/L, 1,95 mg/L, 3,125 mg/L e 5 mg/L) obtidas a partir da diluição do hipoclorito de sódio em clarificado e em licor misto do reator piloto e se observou a mortalidade dos indivíduos ao longo de 96h.Foi possível observar taxas de 100% de mortalidade utilizando as concentrações de 3,125 mg/L e 5 mg/L em clarificado, mas um menor sucesso no licor misto, devido a uma maior complexidade do meio como a presença de matéria orgânica e microrganismos que para além de servir como fonte de alimento dos dafniídeos reagem com o hipoclorito de sódio. Determinou-se com sucesso a DL50 para a população de Daphnia spp. em clarificado (1,795 mg/L). Conclui-se que as Daphnia spp. possuem um elevado grau de sensibilidade ao hipoclorito de sódio, mas devido a diversidade da população bem como as características do meio em que se desenvolvem, será necessário utilizar concentrações mais elevadas e uma aplicação continuada para se conseguir erradicar a população nos decantadores.
The sustainable management of water resources depends on the proper functioning of wastewater treatment plants. In order to meet the limits imposed by law in Portugal, governed by Decree Law 152/97 of June 19, published in Diário da República No. 139/1997, wastewater treatment plants have to ensure that various parameters in the discharge of treated wastewater, such as Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD) and suspended solids (SS) are below the emission limit values. However, there are occurrences that compromise the functioning of the wastewater treatment system and consequently the quality of the final effluent. In the case of this work, a microcrustacean occurred in the secondary decanters of the Fátima WWTP, which, due to its mobility and wide spread, compromised not only the quality of the treated effluent, but also the processes downstream of the decanter. The aim was therefore to study ways of inhibiting the presence of these organisms in the decanter. A pilot biological reactor was set up to replicate the environment in which Daphnia spp. thrive. It was monitored in terms of various immediate parameters (pH, dissolved oxygen, oxidation-reduction potential, temperature, conductivity and total dissolved solids) and analytical parameters (BOD, COD, total and suspended solids, total Kjeldahl nitrogen and phosphorus). After stabilizing the reactor, toxicity tests were carried out using sodium hypochlorite as a toxic agent for daphniids, using different concentrations (0.76 mg/L, 1.22 mg/L, 1.95 mg/L, 3.125 mg/L and 5 mg/L) obtained from diluting sodium hypochlorite in clarified and mixed liquor from the pilot reactor, and the mortality of the individuals was observed over 96 hours.It was possible to observe 100% mortality rates using the concentrations of 3.125 mg/L and 5 mg/L in clarified liquor, but less success in mixed liquor, due to the greater complexity of the medium such as the presence of organic matter and microorganisms which, in addition to serving as a food source for the daphniids, react with the sodium hypochlorite. The LD50 for the Daphnia spp. population in clarified water was successfully determined (1.795 mg/L). It can be concluded that Daphnia spp. have a high degree of sensitivity to sodium hypochlorite, but due to the diversity of the population and the characteristics of the environment in which they develop, it will be necessary to use higher concentrations and continuous application in order to eradicate the population in the decanters.
The sustainable management of water resources depends on the proper functioning of wastewater treatment plants. In order to meet the limits imposed by law in Portugal, governed by Decree Law 152/97 of June 19, published in Diário da República No. 139/1997, wastewater treatment plants have to ensure that various parameters in the discharge of treated wastewater, such as Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD) and suspended solids (SS) are below the emission limit values. However, there are occurrences that compromise the functioning of the wastewater treatment system and consequently the quality of the final effluent. In the case of this work, a microcrustacean occurred in the secondary decanters of the Fátima WWTP, which, due to its mobility and wide spread, compromised not only the quality of the treated effluent, but also the processes downstream of the decanter. The aim was therefore to study ways of inhibiting the presence of these organisms in the decanter. A pilot biological reactor was set up to replicate the environment in which Daphnia spp. thrive. It was monitored in terms of various immediate parameters (pH, dissolved oxygen, oxidation-reduction potential, temperature, conductivity and total dissolved solids) and analytical parameters (BOD, COD, total and suspended solids, total Kjeldahl nitrogen and phosphorus). After stabilizing the reactor, toxicity tests were carried out using sodium hypochlorite as a toxic agent for daphniids, using different concentrations (0.76 mg/L, 1.22 mg/L, 1.95 mg/L, 3.125 mg/L and 5 mg/L) obtained from diluting sodium hypochlorite in clarified and mixed liquor from the pilot reactor, and the mortality of the individuals was observed over 96 hours.It was possible to observe 100% mortality rates using the concentrations of 3.125 mg/L and 5 mg/L in clarified liquor, but less success in mixed liquor, due to the greater complexity of the medium such as the presence of organic matter and microorganisms which, in addition to serving as a food source for the daphniids, react with the sodium hypochlorite. The LD50 for the Daphnia spp. population in clarified water was successfully determined (1.795 mg/L). It can be concluded that Daphnia spp. have a high degree of sensitivity to sodium hypochlorite, but due to the diversity of the population and the characteristics of the environment in which they develop, it will be necessary to use higher concentrations and continuous application in order to eradicate the population in the decanters.
Description
Keywords
Dáfnias Tratamento de águas residuais Sistema de lamas ativadas Hipoclorito de sódio Toxicidade