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Abstract(s)
A entrada de caudais pluviais em redes de drenagem de ĂĄguas residuais Ă© comum e difĂcil de estimar. A sua variação e dimensĂŁo dependem de factores como o estado de conservação da rede de drenagem, alteraçÔes fĂsicas na bacia drenante (e.g. alteração do coberto vegetal ou da ĂĄrea impermeĂĄvel), o nĂvel freĂĄtico e o volume de ĂĄgua pluvial escoado, podendo afectar negativamente o tratamento a jusante e aumentar os encargos para operação e manutenção dos sistemas de ĂĄguas residuais
A partir de dados de precipitação recolhidos em trĂȘs estaçÔes udomĂ©tricas e da delimitação da bacia drenante de Vila Fernando e Vila Fernando Gare (concelho da Guarda), estimou-se o escoamento superficial para o perĂodo entre Janeiro de 2008 e Janeiro de 2009. A medição de caudal efectuada Ă entrada de ETAR de Vila Fernando, para o mesmo perĂodo, permitiu observar que existiu uma proporcionalidade entre o aumento do escoamento pluvial superficial e o caudal
infiltrado que atingiu a ETAR, tendo este Ășltimo sido, em mĂ©dia, cerca de 50% do caudal total detectado Ă entrada daquela infra-estrutura.
Verificou-se, ainda, que o caudal mĂ©dio de origem domĂ©stica (caudal mĂ©dio de tempo seco) foi cerca de 32% inferior ao valor mĂnimo previsto no projecto da ETAR, o que pode ser explicado pela falta de ligação de parte da rede de drenagem afecta Ă ETAR.
A entrada de afluĂȘncias indevidas na ETAR de Vila Fernando afectou o seu desempenho, tendo
contribuĂdo para o aumento da carga hidrĂĄulica e a diminuição do tempo de retenção hidrĂĄulico para valores fora dos intervalos admitidos em projecto, que afectaram a remoção de todos os parĂąmetros analisados. A remoção de CQO, CBO5 e SST, apesar de baixa, duplicou nos meses
com menor pluviosidade, o que significa que o biofilme heterotrófico reagiu melhor à instabilidade causada pela variação de carga hidråulica.
A remoção de azoto e fĂłsforo foi sempre baixa (inferior a 25%), independentemente da presença de caudal de infiltração, tendo o fĂłsforo sido removido associalmente por adsorção. A remoção de azoto (maioritariamente na forma de azoto amoniacal), alĂ©m de baixa, oscilou muito ao longo do temo, tendo sido consequĂȘncia do fraco desenvolvimento de biofilme nitrificante e das plantas.
Estas situaçÔes, além de poderem provocar impactes ambientais negativos e significativos no meio receptor, associado à descarga de cargas poluentes não tratadas, podem constituir um encargo de exploração não esperado para a entidade gestora, quer para a reabilitação da rede de drenagem, quer da ETAR.
The entry of stormwater flow into sewer systems is common and difficult to estimate. Its variation and dimension depend on factors such as the conservation status of the sewer network, physical changes in the drainage catchment (e.g. change in land cover or the impermeable area), the groundwater level and the volume of rainwater runoff, which may adversely affect the downstream wastewater treatment and increase the costs of operation and maintenance of wastewater systems From precipitation data collected at three rainwater measurement points and the drainage catchment of Fernando Vila Fernando Vila Gare (district of Guarda), it was estimated the runoff for the period between January 2008 and January 2009. The flow measurement made at the entrance of the wastewater treatment plant of Vila Fernando, for the same period, allow observing that there was a proportionality between the increase in surface rainwater runoff and the infiltration flow that reached the treatment plant. The latter was, on average, about 50 % of the total flow detected at the entrance of that infrastructure. It was observed that the average flow-rate of domestic wastewater (average dry weather flow) was 32% less than the minimum admitted in project of the wastewater treatment plant, which can be explained by the lack of connection of part of the sewer network in Vila Fernando. The infiltration of rainwater into the sewer network of Vila Fernando affected the performance of the treatment plant, increasing the hydraulic load and decreasing the hydraulic retention time for values outside the ranges allowed in the project, which affected the removal of all parameters. The removal of COD, BOD5 and TSS, although low, has doubled in the months with less rainfall, which means that the heterotrophic biofilm had a better response to the instability caused by the variation of the hydraulic load. The removal of nitrogen and phosphorus were always low (less than 25%), regardless of the presence of infiltration flow, and the phosphorus was removed mainly by adsorption. The removal of nitrogen (mostly in the form of ammonia) fluctuated widely over time, and the low removal rates were associated with the weak development of both nitrifying biofilm and plants. These situations may cause significant negative environmental impacts on the receiving waters, due to the discharge of untreated effluents and may increase unexpected costs for the operation and maintenance of both the sewer network and wastewater treatment plant.
The entry of stormwater flow into sewer systems is common and difficult to estimate. Its variation and dimension depend on factors such as the conservation status of the sewer network, physical changes in the drainage catchment (e.g. change in land cover or the impermeable area), the groundwater level and the volume of rainwater runoff, which may adversely affect the downstream wastewater treatment and increase the costs of operation and maintenance of wastewater systems From precipitation data collected at three rainwater measurement points and the drainage catchment of Fernando Vila Fernando Vila Gare (district of Guarda), it was estimated the runoff for the period between January 2008 and January 2009. The flow measurement made at the entrance of the wastewater treatment plant of Vila Fernando, for the same period, allow observing that there was a proportionality between the increase in surface rainwater runoff and the infiltration flow that reached the treatment plant. The latter was, on average, about 50 % of the total flow detected at the entrance of that infrastructure. It was observed that the average flow-rate of domestic wastewater (average dry weather flow) was 32% less than the minimum admitted in project of the wastewater treatment plant, which can be explained by the lack of connection of part of the sewer network in Vila Fernando. The infiltration of rainwater into the sewer network of Vila Fernando affected the performance of the treatment plant, increasing the hydraulic load and decreasing the hydraulic retention time for values outside the ranges allowed in the project, which affected the removal of all parameters. The removal of COD, BOD5 and TSS, although low, has doubled in the months with less rainfall, which means that the heterotrophic biofilm had a better response to the instability caused by the variation of the hydraulic load. The removal of nitrogen and phosphorus were always low (less than 25%), regardless of the presence of infiltration flow, and the phosphorus was removed mainly by adsorption. The removal of nitrogen (mostly in the form of ammonia) fluctuated widely over time, and the low removal rates were associated with the weak development of both nitrifying biofilm and plants. These situations may cause significant negative environmental impacts on the receiving waters, due to the discharge of untreated effluents and may increase unexpected costs for the operation and maintenance of both the sewer network and wastewater treatment plant.
Description
Keywords
Ăguas residuais - Caudal de infiltação Ăguas residuais - Ăguas fluviais Ăguas residuais - MacrĂłfitas Leito de macrĂłfitas - Remoção de carga