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RESUMEN El estado actual y las continuas alteraciones que aquejan a los humedales ubicados en la ciudad de Bogotá (Colombia), motiva el desarrollo de instrumentos y herramientas, que permitan explicar su comportamiento hidrológico bajo tensiones climáticas, como lo es el fenómeno ENSO. Este artículo presenta la formulación de un modelo de las condiciones hidrológicas del humedal urbano de Torca. La simulación, se realizó con el software Vensim® y la validación estadística del modelo, se efectuó mediante un análisis de sensibilidad multivariable (MVSS), a partir del método Montecarlo. Se evidenció que en los años de ocurrencia del fenómeno climatológico ENSO (2001) y (2011), el patrón de comportamiento de la precipitación y del flujo de entrada (Qi) de la cuenca aferente del humedal fueron paralelos. El tiempo hidráulico de retención (THR) sugirió un comportamiento inverso con relación a la precipitación. En efecto, la precipitación promedio mensual fue de 47,8mm y 158,7mm y el THR promedio fue de 55 días y 33 días, para los años El Niño y La Niña, respectivamente. El flujo de entrada y de salida presentaron un comportamiento paralelo durante el período de estudio, debido, probablemente, a que el cuerpo de agua se convirtió en un cauce de salida. Durante El Niño, cuatro meses registraron desbordamiento del humedal (junio, septiembre, octubre y diciembre), con volúmenes de agua superiores a 130.645m3. Durante La Niña, todos los meses registraron desbordamiento del humedal, a excepción de agosto y septiembre, en donde se observaron volúmenes de agua de 100.018m3 y 109.166m3, respectivamente.
ABSTRACT The current state and the continuous changes that affect the wetlands located in the city of Bogotá (Colombia), motivates the development of instruments and tools that illustrate their hydrological behavior under climatic stresses such as the ENSO phenomenon. This article presents the formulation of a model of the hydrological conditions of the urban wetland of Torca. The simulation was carried out with the Vensim® software and the statistical validation of the model was carried out by means of a multivariate sensitivity analysis (MVSS) using the Montecarlo method. It was evidenced that in the years of occurrence of the ENSO climatological phenomenon (2001) and (2011), the behavior pattern of precipitation and inflow (Qi) of the afferent basin of the wetland were parallel. Hydraulic retention time (THR) suggested an inverse behavior in relation to precipitation. Indeed, the average monthly rainfall was 47,8mm and 158,7mm, and the average THR was 55 days and 33 days for the El Niño and La Niña years, respectively. The inflow and outflow presented a parallel behavior during the study period, probably due to the fact that the body of water became an outlet channel. During El Niño, the wetland overflowed for four months (June, September, October and December), with volumes exceeding 130,645m3. During La Niña, the wetland overflowed every month; except for August and September, where volumes of 100.018m3 and 109.166m3 were observed, respectively.
ABSTRACT
ABSTRACT: The main problem in anaerobic digestion of low-protein residues is the instability caused acidity. The use of limestone at the same time as a neutralizing agent and support material is innovative because stones wear allows the slow release of the calcium carbonate thereby eliminating dispersers. Free calcium content in the system was measured in two plug flow reactors filled with vinasse at initial pH of 4.50. The proportion of 1.8 tonnes of limestone per m³ of vinasse was evaluated at the Hydraulic Retention Times (HRT) of 24, 48, 72, 96 and 120 hours, allowing stabilisation at 96 hours. The ratio of Volatile Acids/Total Alkalinity (VA/TA) ranged from 0.2 to 0.4 and the pH reached 7.0, at the HRT of 120 hours. Increasing the HRT also increased the volatile total solids (VTS) and fixed total solids (TFS) in a similar profile to the measured free calcium content, but calcium remained at the appropriate level of 100 to 250mg l-1. The proportion of limestone/vinasse was adequate to ensure stabilisation, but it is not recommended to reduce the HRT below 96 hours due to the risk of compromising the stability of the anaerobic system.
RESUMO: O maior problema na digestão anaeróbia de resíduos de baixo teor de proteína é a instabilidade por acidez. O uso de calcário ao mesmo tempo como agente neutralizador e material suporte é inovador porque permite eliminar o dosador pois o desgaste das pedras permite a liberação lenta do carbonato de cálcio. O teor de cálcio livre no sistema foi medido em dois reatores tipo Plug flow, preenchidos com vinhaça com pH inicial de 4,50. A proporção de 1,8 toneladas de calcário por m³ de vinhaça foi avaliada com os Tempos de Retenção Hidráulica (TRH) de 24, 48, 72, 96 e 120 horas, permitindo a estabilização em 96 horas. Com um TRH de 120 horas, a relação de Ácidos Voláteis/Alcalinidade (AV/AC) variou de 0,2 à 0,4 e o pH atingiu 7,0. Aumentando o TRH também aumentaram os sólidos voláteis totais (SVT) e sólidos totais fixos (STF) em um perfil semelhante ao teor de cálcio livre medido, mas mantendo níveis adequados de 100 a 250mg L-1. A proporção de calcário/vinhaça mostrou-se adequada para garantir a estabilização, mas não se recomenda a redução do TRH abaixo de 96 horas devido ao risco de comprometer a estabilidade do sistema anaeróbio.
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RESUMO Compreender o comportamento hidrodinâmico de reatores biológicos pode auxiliar na detecção de problemas associados a falhas operacionais e de projeto, situações que prejudicam a eficiência do tratamento. Neste artigo, realizaram-se simulações da fluidodinâmica computacional (CFD) de escoamento de duas fases sólida-líquida de um reator anaeróbio de manta de lodo e fluxo ascendente (UASB), em escala piloto (160 L), com tempo de detenção hidráulica (TDH) de 10 h e vazão de 16 L.h-1. Um modelo Euler-Euler simplificado foi formulado para simular o comportamento hidrodinâmico da zona de reação, influenciada pela configuração do sistema de distribuição do afluente. Foram avaliadas quatro configurações do sistema de distribuição do afluente no reator: uma entrada na parte central (1) e duas entradas centrais (2), de fluxo ascendente; duas entradas nas laterais (3), de fluxo radial; e três entradas de fluxo descendente (4), utilizando geometrias bidimensionais e tridimensionais para verificar a formação de zonas mortas, curtos-circuitos hidráulicos e caminhos preferenciais. As melhores características hidrodinâmicas e a melhor distribuição do afluente foram verificadas na configuração 4, com melhor perfil de mistura do lodo com a fase líquida, na comparação com as demais configurações. Foi notada formação de vórtices na parte inferior do reator com maior concentração do lodo anaeróbio nessa configuração e de caminhos preferenciais nas laterais do reator na configuração 3, indicando mistura ineficiente do afluente com o lodo anaeróbio. O modelo demonstrou que a configuração do sistema de distribuição do afluente influencia significativamente o comportamento hidrodinâmico do reator UASB.
ABSTRACT Understanding the hydrodynamics behavior of biological reactors can help in the detection of problems related to operational failures and design that adversely affect the efficiency of the treatment. In this paper, computational fluid dynamics (CFD) simulations of two-phase liquid-solid flow were carried out in an upflow anaerobic sludge blanket reactor in pilot scale (160 L), with hydraulic retention time (HRT) of 10 h and flowrate 16 L.h-1. The Euler-Euler approach was formulated to simulate the reaction zone hydrodynamics. Four configurations of the influent distribution system in the reactor were evaluated: one central inlet (1) and two central inlets (2), upflow; two lateral inlets (3), radial flow; and three inlets, downflow (4), using two and three-dimensional geometries to verify the formation of dead zones, hydraulic short-circuiting and preferential pathways. Better influent distribution and greater mixture profile of the sludge with the liquid phase were found in the configuration 4, compared to the others by the formation of vortices in the bottom part of the reactor with higher concentration of anaerobic sludge. Formation of preferential pathways was noted in the lateral inlets of the reactor in the configuration 3, indicating an inefficient mixture of the influent with the sludge. The model demonstrates that the configuration of the influent distribution system significantly influences the hydrodynamics behavior of the UASB reactor.
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RESUMO O desenvolvimento da aquicultura intensiva é acompanhado de um crescente impacto ambiental produzido pelos efluentes gerados. Os sistemas de recirculação para aquicultura (SRA) são uma alternativa compacta e trabalham com elevadas densidades de estocagem e menores volumes de água. Foi utilizado um decantador de coluna (DC) associado ao reator aeróbio de leito fluidizado com circulação em tubos concêntricos (BAS-CT) com tempo de retenção hidráulica (TRH) de 0,55 e 0,20 h respectivamente, num SRA com tilápias de 0,32 kg de peso médio e densidade de estocagem de 33,1 kg.m-3 em relação à remoção do nitrogênio amoniacal total (NAT), demanda bioquímica de oxigênio (DBO) e demanda química de oxigênio (DQO). As eficiências na remoção de NAT, DBO e DQO foram 35,2, 48,0 e 64,9%, respectivamente. No uso de DC com o BAS-CT, obteve-se bom desempenho, com baixos TRH no tratamento do efluente.
ABSTRACT The development of intensive aquaculture is accompanied by an increasing environmental impact produced by the wastewater generated. The recirculating aquaculture systems (RAS) are a compact alternative and manage high stocking densities and lower volumes of water. It was used a column settler (CS) associated with aerobic fluidized bed reactor (BAS-CT) with hydraulic retention time (HRT) of 0.55 and 0.20 h respectively, in RAS with tilapias with average weight of 0.32 kg and storage density of 33.1 kg.m-3 regarding the removal of total ammonia nitrogen (TAN), biochemical oxygen demand (BOD) and chemical oxygen demand (COD). The removal efficiencies of TAN, BOD and COD were 35.2, 48.0 and 64.9%, respectively. The use of CS with the BAS-CT showed a good performance with low HRT in the treatment of this effluent.
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RESUMO Esta pesquisa comparou o desempenho de um digestor anaeróbio de lodo sob diferentes estratégias operacionais. Foi avaliada a influência do aumento da carga orgânica volumétrica (COV) (OP I) e o efeito da redução do tempo de detenção hidráulica (TDH) (OP II e OP III) no processo anaeróbio. As cargas aplicadas variaram entre 0,5 e 4,5 kgSV.m-3.d-1 e o TDH foi reduzido de 15 a 5 dias. Produção de gás metano, degradação do material orgânico e a diversidade microbiana foram utilizadas para medição e comparação do desempenho do processo. Foram necessários períodos de aclimatação a cada nova COV aplicada o que levou às instabilidades na remoção de SV e DQO do lodo. A operação com TDH entre 7 e 5 dias apresentou as maiores eficiências de remoção de SV, superiores a 70%, o que influenciou positivamente na estabilidade do processo. As COV aplicadas de 2,5 e 3,5 kgSV.m-3.d-1 resultaram nas maiores produções de metano durante a OP I. Para TDH inferiores a sete dias a produção de CH4 foi prejudicada apesar da existência de microorganismos metanogênicos atuantes no digestor. Comparativamente, a estratégia de redução do TDH resultou em um melhor desempenho do sistema que a fixação da COV. Quanto menor o TDH aplicado, melhor os resultados obtidos na operação do digestor, sugerindo que a eficiência do processo é otimizada em sistemas de alta carga com operação em baixos tempos de detenção hidráulica.
ABSTRACT This study compared the performance of a pilot anaerobic sludge digester under different operating strategies. The influence of increasing organic loading rate - OLR (OP I) and the effect of hydraulic retention time - HRT reduction (OP II and OP III) in anaerobic process were evaluated. The applied loads ranged between 0.5 and 4.5 kgSV.m-3.d-1; HRT was reduced from 15 to 5 days. Production of methane, organic matter degradation and microbial diversity were used to measure and compare the system´s performance. Acclimation periods were taken for each new OLR applied, leading to instabilities in sludge VS and COD removals. The experimental time with HRT between 7 and 5 days showed the highest VS efficiency removals (higher than 70%), which positively influenced process stability. The applied OLR of 2.5 and 3.5 kgVS.m-3.d-1 resulted in higher yields of methane during OP I. CH4 production showed impaired with HRT lower than 7 days, although it was observed active methanogenic microorganisms in the digester. Comparatively, HRT reduction resulted in a better system performance than the increasing OLR approach. The lower HRT applied, the better the results obtained in the operation of the digester, suggesting that the process efficiency is optimized with high load operation at low hydraulic retention times.
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This study reports the performance of University of Cape Town (UCT) municipal wastewater treatment plant, during the startup stage with the focus on the relationship between hydraulic retention time (HRT) and biological nutrient removal (BNR) efficiency. The entire experimental period was 144 days, divided into four periods. Results showed that the removal efficiency of TN, NH4+-N, and Kjeldahl nitrogen (KN) was closely related to the HRT. Furthermore, the biodegradation kinetics analysis was used to calculate the specific degradation rates of pollutants. The GPS-X modeling was also used to examine the effect of the UCT pilot plant on BNR. The UCT pilot plant used in this study achieved high BNR efficiency even during the startup stage. With HRT of 24 hr (Period 1, day 1-40, data set 1-10), the highest levels of TN, NH4+-N and KN removal efficiency were approximately 72, 76 and 78%, respectively. The COD showed consistent high removal efficiency, with the highest level of approximately 96% at HRT of 15 hr (Period 3, day 81-120, data set 21-30). The TP removal efficiency rose at first and subsequently decreased abruptly. The maximum removal efficiency was 85% with HRT of 19 hr (Period 2, day 41-80, data set 11-20). With the optimal HRT 19 hr, the average removal efficiency values of COD, TP, TN, NH4+-N and KN were 89, 80, 65, 67 and 68%, respectively. The GPS-X modeling results indicated that the UCT process was effective in COD, TP and TN removal.
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Se construyó un modelo de simulación dinámica con la intención de explicar el comportamiento del fósforo total en el agua y su relación con el estado trófico del humedal de Jaboque, Bogotá D. C., Colombia. En el modelo se incluyen los flujos de entrada y salida del agua y los aportes de fósforo total en cada una de las tres secciones de la cubeta con características morfométricas y condiciones físicas y químicas del agua muy diferentes. La modelación dinámica se basó en ecuaciones diferenciales y para ella se utilizó el programa computacional Stella 9.1®. En los meses con mayores caudales (época de lluvias), la carga de fósforo disminuye en las tres secciones del humedal, mientras que en los meses con menores caudales (época de sequía), la misma se incrementa. En la sección uno (tercio alto) el valor del índice de estado trófico fue de 45,09 mg/m³ y el tiempo de retención hidráulica de 14 días/año. En la segunda sección (tercio medio) el valor del mencionado índice fue de 35,89 mg/m³ y el THR fue de 34 días/año. Finalmente, en la tercera sección (tercio bajo) los valores fueron 19,5 mg/m³ y 40 días/año respectivamente. Estos valores indican que la primera y segunda sección se encuentran en condiciones de eutrofía y la tercera de mesotrofía. El análisis de sensibilidad permitió estimar que con una carga de 0,62 mg/m³ de fósforo total se podrían mantener las condiciones de mesotrofía en la tercera sección y que para las dos primeras secciones se debería reducir la carga hasta 0,2 mg/m³, para alcanzar un estado de mesotrofía.
A dynamic simulation model to explain the behavior of the total phosphorus in water and its relationship to the trophy status of wetland Jaboque, Bogotá D. C., Colombia, in three sections with particular physical and chemical characteristics is presented. The model includes the inflow and outflow flows of water and total phosphorus contributions in each of the three sections of the wetland with morphometric and water physicochemical conditions very different. The dynamic modelling was based on differential equations; we used the computer program Stella 9.1®. In the months with higher flow (rainy season), the phosphorus load decreases in the three sections of the wetland, while in the months with lower flow (dry season) increases. In section one (third highest) trophy state index was 45.09 mg/m³ and hydraulic retention time of 14 days/year in the second section (middle third) trophy state index was 35.89 mg/m³ and the THR was 34 days/year. In the third section (lower third) values were 5.19 mg/m³ and 40 days/year respectively. These values indicate that the first and second sections are able to eutrophic state and third to mesotrophic. Sensitivity analysis allowed estimating that with a load of 0.62 mg/m³ total phosphorus could be maintained mesotrophic conditions in the third section and for the first two sections should be reduced to 0.2 mg/m³ load to achieve a mesotrophic state.
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Neste trabalho, avaliou-se o efeito do tempo de detenção hidráulica (TDH) no desempenho de três reatores aeróbios inoculados com Aspergillus niger AN400, usados para tratamento de efluentes de refinarias de petróleo. Cada reator foi operado com um tempo de detenção hidráulica diferente: 4, 8 e 12 horas, durante 152 dias. Eles possuíam leito fixo de espuma de poliuretano e o escoamento era ascendente e contínuo. Determinaram-se: pH, fenóis, demanda química de oxigênio (DQO), amônia, nitrito e nitrato, no afluente e efluentes dos reatores. O TDH de oito horas foi o melhor para remoção de DQOsolúvel e não houve diferença entre os TDHs para remoção de fenóis totais. No período estável não houve remoção de nitrato; no entanto ocorreu remoção de nitrito de aproximadamente 99 por cento. Além disto, houve produção de amônia devido à amonificação a partir do nitrito presente no meio.
This paper evaluated the effect of hydraulic retention time (HRT) on the performance of three upflow aerobic reactors, with polyurethane foam as support material, inoculated with Aspergillus niger AN400, used for the treatment of petroleum refinery wastewater. Each reactor was operated with a different HRT: 4, 8 and 12 hours, during 152 days. The performance was evaluated based on pH; phenols; COD, nitrate and nitrite. The results show that for the COD removal, it is more reasonable to operate the reactor with HRT of eight hours. However, there was no difference among results of phenol removal efficiency of the different HRTs. During steady state condition, nitrite was removed in approximately 99 percent, but there was no reduction on the nitrate concentration. Ammonia was produced in all reactors, probably due to ammonification of nitrite.