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- Effect of vegetation on the performance of horizontal subsurface flow constructed wetlands with lightweight expanded clay aggregatesPublication . Mesquita, Maria da Conceição; Albuquerque, Antonio; Amaral, Leonor; Nogueira, ReginaThis 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.
- The influence of evapotranspiration on vertical flow subsurface constructed wetland performancePublication . Bialowiec, Andrzej; Albuquerque, Antonio; Randerson, PeterThis paper presents an example of the importance of evapotranspiration in constructed wetlands, with vertical subsurface flow, comparing different methods of treatment efficiency calculations and discussing the influence of evapotranspiration on removal rates. The application of reed, marked by high transpiration ability, is a cheap and effective method of landfill leachate disposal. A 2-year study examined the effectiveness of leachate treatment in constructed wetlands with reed. Two kinds of vertical subsurface flow systems: first with sand, and second with combined two layers of sewage sludge and sand has been tested. 1, 3, and 5 mmd(-1) hydraulic loading rates of landfill leachate have been applied. Daily evapotranspiration was in the range from 0.98 to 2.99 mmd(-1) in the first year of research and from 2.56 to 4.61 mmd(-1) in the second year. The influence of evapotranspiration rate on chemical oxygen demand (COD) removal rate was examined. Two methods of removal efficiency calculation have been used: first based on inlet and outlet COD concentrations, second on mass balance determination. Research showed that the removal efficiency calculated as a comparison between initial and final concentration is significantly lower, than expected from mass balance, especially, when higher hydraulic loading rates were applied.
- Nitrogen removal from landfill leachate in constructed wetlands with reed and willow: Redox potential in the root zonePublication . Bialowiec, Andrzej; Albuquerque, Antonio; Davies, Laura; Randerson, PeterThis 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.
- Influence of stormwater infiltration on the treatment capacity of a LECA-based horizontal subsurface flow constructed wetlandPublication . Amado, Lígia; Albuquerque, Antonio; Espírito Santo, AntónioThis research work evaluates the impact of stormwater infiltration on the removal of organics, solids, nitrogen and phosphorus in a LECA-based horizontal subsurface flow constructed wetland. Stormwater runoff for the period between January 2008 and June 2010 (30 months) was estimated for the drainage basin of the Vila Fernando wastewater treatment plant (constructed wetland system) and it was observed proportionality between the increase in surface runoff and the infiltration flow rate that reached the plant. The average stormwater infiltration rate that reached the plant was 67.4 m(3) d(-1) (77% of the influent flow rate into the plant). The 30 month monitoring campaign set up at one of the reed beds showed that stormwater infiltration led to a high variation of the hydraulic loading rate (HLR) throughout the bed, which affected its performance in the removal of organic matter, suspended solids and nitrogen. For a HLR below 20 cm d-1 the removal efficiencies for BOD5, COD and TSS doubled. The removal of nitrogen was too low and was associated with the weak development of nitrifying biofilm and the poor growth of reeds. However, it was observed a good relationship between the applied and removed loads for most of the parameters, which seems to indicate that the organic, solid, nitrogen and phosphorus loading rates influenced the respective removal rates. The use of a bed material with high specific surface area, such as LECA, can only improve the treatment capacity of horizontal subsurface flow systems if the organic and solid loading rates, as well as the HLR, can be effectively controlled.
- Spatial Variation of Longitudinal Dispersion in LECA-Based Vegetated BedsPublication . Albuquerque, AntonioThe evaluation of the dispersion in vegetated beds may allow indentifying mechanisms that affect the transport and reaction of solutes, namely organic and nitrogen compounds. A set of non-reactive tracer experiments (slag injection) was performed in a vegetated bed (a mesocosm with a LECA-based substratum and colonized with Phragmites australis) used for the removal of organic and nitrogen pollutant loads. Loads of approximately 300 mg COD/L and 30 mg NH4-N/L and a hydraulic loading rate of 3.5 cm/d were used. The results showed a delay in all the residence time distribution (RTD) curves and a variation in the dimensionless residence time (mu((m,theta))) of the E(theta) curves, which means that the mass centre of the impulse was late relatively to the expected one. A strong dispersion and tracer retention (due to the presence of stagnated areas and internal recirculation) was observed, especially in the first 33 cm of the bed, which seems to have been related to the presence of complex clusters of roots, solid material, biofilm and LECA particles. An analytical solution of the Multiple-Tanks-in-Series (MTS) model well represents the RTD curves obtained in the tracer experiments. The detected dispersion and dead volume ratios (7% to 12%) did not affect the performance of the bed, which presented mean removal efficiencies of 85% and 60.4% for COD and NH4-N, respectively.