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- Removal of organic matter and nitrogen in an horizontal subsurface flow (HSSF) constructed wetland under transient loadsPublication . 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.
- 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.
- The influence of evapotranspiration on wastewater constructed wetland treatment efficiencyPublication . Albuquerque, António; Bialowiec, Andrzej; Randerson, PeterOwing to low investment and maintenance costs, there has been a growing interest in applying plants in wastewater treatment. Plants commonly used in constructed wetlands (CW) include: cattail, reed, rush, yellow flag, manna grass, and willow. In a CW, application of plants brings several benefits: creating aerobic conditions in the otherwise anaerobic rhizosphere, providing carbon compounds into the rhizosphere, uptaking pollutants (e.g. nutrients and heavy metals) from treated wastewater; improving the hydraulic conditions of wastewater flow through CW beds, and also increasing the available surface for growth of microbial biofilms. Hydrophytes also have great transpiration potential. Numerous studies have shown the importance of evapotranspiration during hot periods in natural wetlands and also in constructed wetlands. Evapotranspiration affects treatment efficiency in CWs: it increases the concentration of dissolved compounds due to decreasing water volume. Therefore, having regard to the mode of operating (VSSW or HSSW), temperature and influent characteristics (e.g. HLR and wastewater influent loads), the removal efficiency calculated as a comparison between initial and final concentration is lower, than expected from mass balance. Given results from systems in colder (Poland) and warmer (Portugal) climate conditions shows that the difference in methodology of removal efficiency calculation is significant, even if the CWs are operating in different modes. Usually, in the literature removal efficiency is expressed on the basis of concentrations, mostly due to lack of flow rate monitoring. Unfortunately, this may seriously underestimate treatment performance of CWs. This study suggests the need for routine monitoring of flow rate, or evaluation of potential evapotranspiration, to estimate removal efficiency of a CW based on mass balance.