Damköhler number distributions and constituent removal in treatment wetlands

R ESU M OObjetivou-se, com a realização deste trabalho, obter o ajuste do modelo matemático adaptado de cinética de primeira ordem e os respectivos parâmetros cinéticos para descrição da degradação da matéria orgânica em SACs cultivados com lírio amarelo (Hemerocallis flava), no tratamento de esgoto doméstico. Os SACs foram cultivados com lírio amarelo e submetidos a diferentes taxas de carregamento orgânico superficial (TCOs) de esgoto doméstico: 44; 98; 230 e 395 kg ha -1 d -1 de DBO. O modelo matemático adaptado de decaimento do material orgânico apresentou bom ajuste e descreveu adequadamente a cinética de remoção de matéria orgânica (DQO) nos sistemas avaliados apresentando, geralmente, R 2 superior a 75%. Em ordem crescente de TCO valores de coeficientes de degradação (Kv) foram, respectivamente, de 0,45; 0,69; 1,23 e 1,72 d -1 , considerados baixos para os dois primeiros SACs e normais para os outros dois, e os valores de "n" de 0,448; 0,107; 0,327 e 0,461, na faixa normalmente encontrada na literatura. Palavras-chave: wetlands construídos, plantas ornamentais, cinética de degradaçãoOrganic matter removal kinetics in constructed wetlands cultivated with yellow lily A B ST R A C T This work aimed to obtain the adjustment of the mathematical model adapted from the first order kinetics and its respective parameters for describing the organic matter degradation in constructed wetlands (CWs) planted with yellow lily (Hemerocallis flava) for the treatment of domestic sewage. The CWs were cultivated with yellow lily and subjected to different surface organic loading rates (TCOs) of domestic sewage: 44, 98, 230 and 395 kg ha -1 day -1 BOD. The mathematical model adapted from the decay of organic material showed a good fit and adequately described the kinetics of removal of organic matter (COD) in the evaluated systems, with generally more than 75% R 2 . In ascending order of TCO values of degradation coefficients (Kv) were, respectively, of 0.45, 0.69, 1.23 and 1.72 d -1 , considered low for the first two CWs and normal for the other two, and the values of "n" of 0.448, 0.107, 0.327 and 0.461 in the range normally found in the literature.

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“…Esta abordagem ignora a influência de fatores como precipitação, evapotranspiração e padrões de escoamento não ideal (Carleton, 2002).…”

Section: Introductionunclassified

Cinética de remoção de matéria orgânica em sistemas alagados construídos cultivados com lírio amarelo

Chagas

Matos²,

Cecon³

et al. 2011

Rev. bras. eng. agríc. ambient.

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“…Damköhler numbers result from the ratio between the temporal scales of reaction and transport (e.g., Carleton 2002). We used the following expressions:…”

Section: Range Of Applicability Of the Free-boundary Solutionmentioning

confidence: 99%

Porewater nitrate profiles in sandy sediments hosting submarine groundwater discharge described by an advection–dispersion-reaction model

Ibánhez¹,

Leote

Rocha³

2010

Biogeochemistry

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In order to separate the effects of reaction from those of transport on vertical porewater concentration profiles of nitrate at an intertidal groundwater seepage site (Ria Formosa, Portugal), a freeboundary solution of an Advection-Dispersion-Reaction (ADR) model was used to describe the shape of NO 3 -concentration profiles collected in situ. The model includes three sequential reaction layers, postulated with basis on the local distribution of the benthic organic C:N ratio and major identifiable changes in concentration gradients with depth. The advective nature of the system was used to propose a mass balance simplification to the constitutive equations permitting a free-boundary solution, which in turn allowed prediction of sediment-water fluxes of NO 3 -. Sensitivity analysis confirmed that in similarly advective-dominated environments, both the porewater concentration distribution and the interfacial fluxes are strongly dependant on seepage rate and benthic reactivity. The model fitted the measured profiles with high correlation (usually higher than 90%), and model-derived sediment-water NO 3 -fluxes were in good agreement to fluxes measured in situ with Lee-type seepage meters (0.9948 slope, R 2 = 0.8672, n = 8). Nitrate oxidation and reduction rates extracted from model fits to the data (10 -2 -10 0 mmol m -2 h -1 ) agreed with literature values. Because dispersive effects are not included in direct mass balances based on the porewater concentrations, the model presented here increases the accuracy of apparent reaction rate estimates and geochemical zonation at Submarine Groundwater Discharge (SGD) sites. The results establish the importance of sandy sediments as reactive interfaces, able to modulate mass transfer of continental-derived contaminants into coastal ecosystems. We suggest that tools such as the one described here might be used to advantage in preparing further experimental studies to elucidate how benthic reactivity affects nitrate distribution and fluxes in sediments affected by SGD.

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“…For illustrative purposes, the wetland depicted in Fig. 1 is assumed to consist of three equal-sized tanks, as this number of tanks is considered reasonable for most wetlands [2,17]. Following the illustration, the results are generalized to an arbitrary set of N tanks.…”

Section: Conceptual Modelmentioning

confidence: 99%

“…Hydrodynamic dispersion is the net result of variable advection and diffusion and can be rigorously modeled using plug flow with dispersion (PFD) reactor models [20]. Alternatively, a tanks-in-series approach can also be used [9] and has been adopted by several researchers (e.g., [2,14,24]) to characterize incomplete pollutant mixing in wetlands. This approach is intuitive and provides results comparable to a PFD model.…”

Section: Introductionmentioning

confidence: 99%

An Analytical Solution to Model Aquaculture Wetlands Subject to Intermittent Loading and Variable Initial Concentrations

Uddameri

2009

Environ Model Assess

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Constructed wetlands are increasingly being used to treat intermittent releases of wastewaters from aquaculture ponds. Most constructed wetland design protocols are based on steady-state releases and as such are incapable of characterizing transient pollutant distribution arising from intermittent releases. Given the seasonal nature of aquaculture operations, the constructed wetland has to be developed using water from other nearby sources (termed as fill water in this study). In some instances, the pollutant concentrations in the fill water are noted to be greater than that measured in the aquaculture ponds. Also, the pollutants in the wetland may exhibit spatial variability due to geochemical interactions with wetland soils. These effects cannot be captured with existing steady-state design schemes. A mathematical model based on the tanks-in-series conceptualization is developed to overcome the aforementioned limitations. An analytical solution for multiple intermittent releases and spatially varying initial concentrations is obtained using Laplace transform and superposition techniques. The utility of the developed model is illustrated using an example based after a constructed wetland at the Loma Alta Shrimp Aquaculture Facility (LASAF) in South Texas. The developed model captures the extremely nonlinear relationship between the maximum discharge concentration and the hydraulic residence time. For the conditions assumed in this study, the extent of mixing is not of major concern when the spacing between the loadings is greater than 0.75 times the hydraulic residence time (HRT). Model results also suggest that the wetland should be oriented in a manner such that the internal geochemical production of the pollutant, if any, is near the inlet.

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Damköhler number distributions and constituent removal in treatment wetlands

Cited by 41 publications

References 15 publications

Cinética de remoção de matéria orgânica em sistemas alagados construídos cultivados com lírio amarelo

Cinética de remoção de matéria orgânica em sistemas alagados construídos cultivados com lírio amarelo

Porewater nitrate profiles in sandy sediments hosting submarine groundwater discharge described by an advection–dispersion-reaction model

An Analytical Solution to Model Aquaculture Wetlands Subject to Intermittent Loading and Variable Initial Concentrations

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