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- Analysis of hydrodynamic characteristics of a horizontal subsurface flow constructed wetlandPublication . Albuquerque, António; Bandeiras, RodrigoHorizontal subsurface flow (HSSF) constructed wetlands are widely used for wastewater treatment but there’s still a lack of information on flow characteristics changes throughout the porous bed over time. The continuous growth of roots, the adsorption, sedimentation and precipitation of wastewater compounds and the biofilm release over operation time leads to the development of stagnated areas, the appearance of hydraulic short-circuiting and variations in dispersion conditions, which affect substrate distribution throughout the bed and, therefore, may worsen the overall performance of the system. In order to enable a better understanding of the transport mechanisms throughout the bed, two series of tracer tests were performed in a laboratory HSSF system at the hydraulic loading of 4.7x10-3 m3 m-2 h-1. The first series was executed with the bed without vegetation and the second with the bed already colonized with Phragmites australis after an operation period of eight months at an average organic loading of 12 g m-2 d-1 COD. The magnitude of longitudinal dispersion was estimated both by a curve- fitting technique using the non-linear least square optimization method (LSOM) and using the moment method (MOM) over the advection-dispersion-reaction equation. The flow regime and the extension of dead volumes were estimated by the same curve-fitting technique over the multiple tanks in series model (MTS). The results showed that the development of plants and biomass did not contribute for a significant amount of longitudinal dispersion in the overall media length. However, the dispersion was very strong in the inlet section, where the dead volumes increased approximately 65% within the colonized bed. The flow regime may be considered as plug flow throughout the overall length and the tracer retention was associated with dispersion and internal recirculation and, additionally, for Series II it was associated with the occurrence of clusters of biomass and roots. The MTS better explain the tracer results for the overall media length. The MOM seems to be inadequate for estimating Pe leading to underestimated values when compared with the ones calculated by LSOM.
- Evaluation of the simultaneous removal of organic matter, nitrogen and suspended solids in a SSHF constructed wetland in Capinha, PortugalPublication . Arendacz, Mirosława; Obarska-Pempkowiak, Hanna; Albuquerque, António; Correia, Maria; Borges, MiguelComparing with other countries there is still a lack of experience in applied constructed wetlands for wastewater treatment in Portugal. Among all Mediterranean countries only France and Italy established the guidelines on Constructed Wetlands (CWs). In most of those countries as well as in Portugal there are no specific regulations and design criteria of CWs for the treatment of wastewater [1]. Most of the CWs applied in Mediterranean countries were designed basing on northern countries experience; therefore there is a great need to establish regulations suitable for warm climate conditions. Additionally, the extending popularity of CW systems and a need to make more researches is forced by the Urban Wastewater Treatment Directive (91/271/EEC) and Water Framework Directive (2000/60/EEC), which set the goals to achieve certain standards of discharge water in Europe by the 2015 year. The advantages of CWs application in Portugal are unquestionable: low energy and maintenance requirements, low cost and appropriateness for domestic wastewater treatment for small and rural communities. Moreover, the land availability and temperature are not the limiting factors. As almost 25% of 5 Mirosława Arendacz, Hanna Obarska-Pempkowiak, Antonio Albuquerque, Maria Correia, Miguel Borges the population of central Portugal lives in small and rural agglomerations CWs seem to be very attractive solution. The majority of constructed wetlands in Portugal are designed as surface horizontal flow systems for secondary treatment of municipal and domestic sewage [2, 3]. There is very little date on the treatment efficiency of CWs in Portugal so far, however it had been reported that they show good performance in terms of BOD5 , TSS and lower effectiveness for total P and N removal. High capacity to remove low concentration of organic substances was also observed [2]. Data obtained on the treatment efficiency of CWs in Mediterranean countries also proved good potential of CWs to organic removal (COD, BOD5, and TSS) as well as to ammonia removal, which enabled meeting discharge criteria set by governments [1]. The survey conducted for CWs in Spain reported that the loadings applied for horizontal flow systems were in range of 0.8÷20.3 g BOD5 /m2day and 3÷17 g TSS/ m2day [4]. Data obtained in Spain showed that the average load applied to horizontal flow constructed wetlands is higher that ones cited in the literature and proved that those systems perform very well in terms of organic matter removal comparing to the other European countries [4]. This conclusion could also apply to Portugal due to similar climate conditions, close localization and similar regulations and criteria taken into account for sizing. However, more accurate data must be provided in order to approve it and to establish the most guidelines criteria. The objective of the paper was to evaluate the performance of the subsurface horizontal flow (SSHF) submerged constructed wetland in Capinha, located in the central Portugal, mostly in terms of organic matter (COD), nitrogen forms (total N, ammonia and nitrate) and suspended solids (TSS). The aim of the work was also to study the effect of loads on the removal of above pollutants.