EVAWET - Evaluation of the hydrodynamic and environmental behaviour of constructed wetlands for wastewater treatment and reuse

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Organizational Unit

Publications

Avaliação da influência da vegetação na variação das características hidrodinâmicas em leitos de escoamento subsuperficial e horizontal

Publication . Bandeiras, Rodrigo Mendonça; Albuquerque, António João Carvalho de

A avaliação das condições de escoamento em leitos de escoamento subsuperficial e horizontal (LESH) é essencial para a detecção de mecanismos que podem provocar quebra de rendimento na remoção de poluentes (e.g. zonas pouco irrigadas, zonas de volume morto, curto-circuito hidráulico, recirculações internas e dispersão). Realizaram-se duas séries de ensaios de traçagem em dois LESH laboratoriais, um sem vegetação e o outro plantado com Phragmites australis, cerca de um ano após o seu arranque, para cargas orgânicas de 10,6 g CQO m-2 d-1 e cargas de azoto de 1,1 g N-NH4 m-2 d-1 e uma carga hidráulica de 0,035 m3 m-2 d-1. Utilizou-se o tipo de impulso discreto, tendo a resposta sido detectada em 3 pontos de amostragem localizados a 0,33 m, 1 m e 1,9 m relativamente ao local da injecção de traçador. Os resultados permitiram concluir que, independentemente da presença de vegetação, a dispersão foi forte em todos os troços dos leitos, com maior intensidade nos primeiros 33 cm do leito sem vegetação, onde se registaram condições de mistura e a presença de maior percentagem de volume morto. O atraso detectado na saída de traçador em todos os ensaios, terá estado relacionado com a presença de maiores extensões de zonas pouco irrigadas, embora tenham também ocorrido zonas de volume morto, com maior predominância no troço inicial do leito sem vegetação. A presença de vegetação parece ter tido um efeito benéfico no controlo das condições hidrodinâmicas, em particular em zonas sujeitas a maior perturbação hidrodinâmica como são as que estão próximas do ponto de alimentação. A solução analítica do modelo de advecção-dispersão-reacção utilizada, representa satisfatoriamente as curvas de distribuição de tempos de residência obtidas, com melhores resultados nos ensaios com vegetação, e permitiu verificar que a presença de vegetação atenua a variação da dispersão ao longo do leito. O rendimento da remoção, quer de CQO, quer de N-NH4, diminuiu com o aumento, quer de Vm, quer de Nd, independentemente do tipo de leito, tendo, no entanto, a queda sido mais acentuada no leito sem vegetação. Assim, a utilização de vegetação em LESH, além de contribuir para a diminuição, quer da dispersão longitudinal, quer de volume morto, retarda a colmatação do leito, permitindo manter um rendimento de remoção elevado, quer de matéria orgânica, quer de azoto.

2009-08Master thesis

Open access

Removal of organic matter and nitrogen in an horizontal subsurface flow (HSSF) constructed wetland under transient loads

Publication . Albuquerque, Antonio; Arendacz, M.; Gajewska, M.; Obarska-Pempkowiak, Hanna; Randerson, Peter; Kowalik, P.

A monitoring campaign in a horizontal subsurface flow constructed wetland under the influence of transient loads of flow-rate, organic matter, nitrogen and suspended solids showed an irregular removal of COD and TSS and lower both removal efficiencies and mass removal rates than the ones observed in other studies for similar operating conditions. This circumstance is associated to the presence of large amount of particulate organic matter from non-point sources. The mass removal rate of ammonia increased 39% as both the water and soil temperatures increased from weeks 1–8 to weeks 9–14. A good correlation between mass load and mass removal rate was observed for all measured parameters, which attests a satisfactory response of the bed under to transient load.

2009Journal article

Open access

Nitrogen removal from landfill leachate in constructed wetlands with reed and willow: Redox potential in the root zone

Publication . Bialowiec, Andrzej; Albuquerque, Antonio; Davies, Laura; Randerson, Peter

This study investigated the effects of reed and willow on bioremediation of landfill leachate in comparison with an unplanted control by measuring redox potential levels in the rhizosphere of microcosm systems in a greenhouse. Plants had a significant influence on redox potential relative to the plant-less system. Redox potential in the reed rhizosphere was anoxic (mean -102 +/- 85 mV), but it was the least negative, being significantly higher than in the willow (mean -286 +/- 118 mV), which had the lowest Eh. Redox potential fluctuated significantly in the willow rhizosphere during daylight hours, with large decreases in the morning. Levels of NH4+ decreased significantly in the first day of the experiment and remained at similar low levels in all three variants for the next four weeks of the experiment. Following this removal of ammonia significant peaks in NO2- occurred in the control and reed tanks on the 1st day, and again on 14th day in the control tank up to 13 mg/dm(3). In the willow tank there was also one significant peak of NO2- in the first week, but only up to 0.5 mg/dm(3). Significant accumulation, within 21 days of NO3- in all variants was observed, but in tanks with reed and willow the concentration of NO3- remained significantly lower (<4 mg/dm(3)) than in the unplanted tank (similar to 35 mg/dm(3)). Final levels of total-nitrogen, nitrate and chemical oxygen demand were considerably lower in the reed and willow tank than in the unplanted tank.

2012-04Journal article

Open access

Application of GIS-based multi-criteria analysis for site selection of aquifer recharge with reclaimed water

Publication . Pedrero, Francisco; Albuquerque, Antonio; Monte, Helena Marecos do; Cavaleiro, Victor; Alarcon, Juan Jose

Reclaimed water from small wastewater treatment facilities in the rural areas of the Beira Interior region (Portugal) may constitute an alternative water source for aquifer recharge. A 21-month monitoring period in a constructed wetland treatment system has shown that 21,500 m3 year−1 of treated wastewater (reclaimed water) could be used for aquifer recharge. A GIS-based multi-criteria analysis was performed, combining ten thematic maps and economic, environmental and technical criteria, in order to produce a suitability map for the location of sites for reclaimed water infiltration. The areas chosen for aquifer recharge with infiltration basins are mainly composed of anthrosol with more than 1 m deep and fine sand texture, which allows an average infiltration velocity of up to 1 m d−1. These characteristics will provide a final polishing treatment of the reclaimed water after infiltration (soil aquifer treatment (SAT)), suitable for the removal of the residual load (trace organics, nutrients, heavy metals and pathogens). The risk of groundwater contamination is low since the water table in the anthrosol areas ranges from 10 m to 50 m. On the other hand, these depths allow a guaranteed unsaturated area suitable for SAT. An area of 13,944 ha was selected for study, but only 1607 ha are suitable for reclaimed water infiltration. Approximately 1280 m2 were considered enough to set up 4 infiltration basins to work in flooding and drying cycles.

2011-11Journal article

Open access

Effect of vegetation on the performance of horizontal subsurface flow constructed wetlands with lightweight expanded clay aggregates

Publication . Mesquita, Maria da Conceição; Albuquerque, Antonio; Amaral, Leonor; Nogueira, Regina

This research evaluates the effect of both organic and ammonia loading rates and the presence of plants on the removal of chemical oxygen demand and ammonia nitrogen in horizontal subsurface flow constructed wetlands, 2 years after the start-up. Two sets of experiments were carried out in two mesocosms at different organic and ammonia loading rates (the loads were doubled); one without plants (control bed), the other colonized with Phragmites australis. Regardless of the organic loading rate, the organic mass removal rate was improved in the presence of plants (93.4 % higher for the lower loading rate, and 56 % higher for the higher loading rate). Similar results were observed for the ammonia mass removal rate (117 % higher for the lower loading rate, and 61.3 % higher for the higher loading rate). A significant linear relationship was observed between the organic loading rate and the respective removal rates in both beds for loads between 10 and 13 g m(-2) day(-1). The presence of plants markedly increase removal of organic matter and ammonia, as a result of the role of roots and rhizomes in providing oxygen for aerobic removal pathways, a higher surface area for the adhesion and development of biofilm and nitrogen uptake by roots.

2013-05Journal article

Open access