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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.
- Longitudinal dispersion in a horizontal subsurface flow constructed wetland: a numerical solutionPublication . Araújo, A.; Sousa, Ercilia; Albuquerque, AntonioWe present a numerical solution for the dead zone model which describes the solute transport in a subsurface and horizontal flow constructed wetland. This model is a system of two mass balance equations for two conceptual areas: the main channel and the storage zone. We use finite difference schemes to determine the numerical solution of the system and we study its convergence by presenting properties related to the stability and accuracy of the schemes. Concerning the experimental results, the magnitude of the longitudinal dispersion and the extension of dead volumes is estimated for clean conditions and after a certain operating period under organic loading conditions. The results showed a considerable amount of longitudinal dispersion through the bed, which was very strong near the feeding point, indicating the occurrence of mixing and significant presence of dead zones and short-circuiting.
- Contribuição para o estudo da remoção de residuais de carbono em filtros biológicos de leito imerso e fluxo descendentePublication . Albuquerque, Antonio; Santana, Fernando José PiresOs sistemas de tratamento biológicos convencionais não removem a totalidade dos constituintes presentes nas águas residuais domésticas, sendo frequente a presença nos seus efluentes de residuais (e.g. matéria orgânica solúvel, biodegradável ou refractária, produtos resultantes da actividade microbiológica e compostos inorgânicos solúveis) que podem causar impactes ambientais significativos nas massas hídricas e no solo, nomeadamente nos seus potenciais usos. Quando o meio receptor é sensível à descarga destes constituintes remanescentes ou, a jusante é utilizado para determinados usos, é necessário efectuar a sua remoção, podendo ser utilizados sistemas de tratamento avançados ou de afinação como é o caso dos filtros biológicos de leito imerso. Apesar de existirem vários estudos sobre a aplicabilidade destes sistemas na eliminação de nutrientes, a sua utilização para a remoção de residuais de carbono não tem sido, contudo, avaliada. Nestes termos, o objectivo principal deste trabalho centrou-se no estudo da biodegradação de residuais de carbono, comuns em efluentes de tratamento secundário de águas residuais urbanas e água bruta de origem superficial, através da utilização de um filtro biológico de leito imerso, tendo, complementarmente, sido estudada a remoção de azoto (amónio e formas oxidadas de azoto). Realizaram-se ensaios complementares para o estudo das condições hidrodinâmicas no filtro e ensaios para avaliar as condições básicas de operação, tendo em atenção a estabilidade do processo e a evolução da perda de carga no leito ao longo do tempo. Nos ensaios de biodegradação foram utilizados substratos simples (acetato) e complexos (água residual doméstica e água de origem superficial), tendo-se testado diferentes condições de carga (carga orgânica aplicada e razão C/NH4+-N) e de operação (arejamento, ciclo de lavagem e número de passagens pelo leito). Os resultados permitiram concluir, para a gama de cargas orgânicas (5,2 g C m-3 h-1 a 77,3 g C m-3 h-1) e de azoto amoniacal (0,2 g NH4+-N m-3 h-1 e 38,7 g NH4+-N m-3 h-1) aplicadas, que o filtro utilizado permitia obter remoção carbonada, nitrificação e desnitrificação, a taxas de eliminação satisfatórias. Não se observou, contudo, remoção de qualquer dos compostos para cargas inferiores a 5,2 g C m-3 h-1 e 1,5 g NH4+-N m-3 h-1. A remoção mais importante, quer de carbono, quer de azoto amoniacal, foi observada no intervalo de cargas orgânicas médias entre 25,7 g C m-3 h-1 e 77,3 g C m-3 h-1, em particular na parte superior do leito (8,0 cm iniciais) onde ocorreu forte dispersão, o oxigénio dissolvido apresentou as concentrações mais elevadas, foram observadas maiores produções de biomassa e uma camada de biofilme mais densa. A adopção de uma segunda passagem pelo leito contribuiu para o aumento da remoção de ambos os compostos, apenas para cargas orgânicas médias superiores a 25,7 g C m-3 h-1. Os resultados permitiram, ainda, constatar que a remoção de formas oxidadas de azoto, essencialmente constituídas por nitratos, independentemente do tipo de substrato e das condições de carga e de operação utilizadas, ocorreu, principalmente, por desnitrificação. Nestes termos, a utilização de filtros biológicos de leito imerso para a remoção de residuais de carbono, poderá constituir alternativa económica e tecnicamente vantajosa tendo em vista, quer a redução de impactes ambientais de descargas em meios hídricos e no solo, quer a produção de efluentes com potencial de reutilização, podendo, complementarmente, ser obtida a remoção de azoto.
- 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.
- Influence of bed media characteristics on ammonia and nitrate removal in shallow horizontal subsurface flow constructed wetlandsPublication . Albuquerque, Antonio; Oliveira, José; Semitela, Sabrina; Amaral, LeonorTwo bed media were tested (gravel and Filtralite) in shallow horizontal subsurface flow (HSSF) constructed wetlands in order to evaluate the removal of ammonia and nitrate for different types of wastewater (acetate-based and domestic wastewater) and different COD/N ratios. The use of Filtralite allowed both higher mass removal rates (1.1 g NH4–N m−2 d−1 and 3 g NO3–N m−2 d−1) and removal efficiencies (>62% for ammonia, 90–100% for nitrate), in less than 2 weeks, when compared to the ones observed with gravel. The COD/N ratio seems to have no significant influence on nitrate removal and the removal of both ammonia and nitrate seems to have involved not only the conventional pathways of nitrification–denitrification. The nitrogen loading rate of both ammonia (0.8–2.4 g NH4–N m−2 d−1) and nitrate (0.6–3.2 g NO3–N m−2 d−1) seem to have influenced the respective removal rates.
- Investigations of nitrogen removal pathways in a biological packed bed reactor using elementary mass balancesPublication . Albuquerque, Antonio; Makinia, Jacek; Pagilla, KrishnaNitrogen cycle involves a complex set of potential biochemical pathways with reactions catalyzed by different microorganisms. Elementary mass balances for COD, DO, NH4-N and alkalinity were conducted and stoichiometric relationships were investigated to explain possible pathways of the nitrogen removal mechanisms in a lab-scale submerged down flow biological packed bed (BPB) reactor. Four sets of experiments were performed by modifying the organic loading and C/N ratio in comparison with steady-state conditions. Approximately 90% of COD and NH4-N removal occurred in two upper sections occupying 1/5 of the reactor height. The elementary mass balances could not explain all the experimental results with respect to nitrogen removal and oxygen consumption by known mechanisms. The mass balance calculations, excluding the possibility of nitrification, were in general in accordance with the observations indicating no or minimal NO3-N production. The theoretical stoichiometric requirements for nitrification reaction were satisfied in 6 experiments and in another 8 experiments nitrification may have occurred, but stoichiometry was not satisfied. Using C/N ratio as the variable, only at C/N ratio = 10, the predictions confirmed the possibility of nitrification in the same 3 (out of 4) assays as observed in practice. The results of this study reveal that the nitrogen transformations occurring in the studied reactor are complex and cannot be explained by simple mechanisms of microbial assimilation and nitrification
- 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.