Despite the fact that several authors consider the available measurement methods of hydraulic conductivity (k) suitable for a good representation of the bed condition and clogging potential in horizontal subsurface flow constructed wetlands, others have questioned their adequacy. In this work, hydraulic conductivity measurements with conventional and modified methods were undertaken in two small full-scale units, one planted with cattail (Typha latifolia) and the other unplanted. Both units had already been operating for seven years and showed a high degree of clogging. It was observed that the use of the falling head method, with the introduction of the tubes during the test, provided results without a clear spatial trend. On the other hand, tests done on monitoring wells inserted during construction time showed, as expected, k increasing with the horizontal distance from the inlet, but without reflecting actual field conditions. It was observed that, as the bed became more clogged, the use of the reported methods became more complex, suggesting the need of other methodologies. The use of planted fixed reactors (removable baskets installed in the bed) with evaluation of k at constant head in the laboratory showed potential for the characterization of the hydrodynamic properties of the porous medium.
This study presents a novel method for investigations on undisturbed samples from full-scale horizontal subsurface-flow constructed wetlands (HSSFCW). The planted fixed bed reactor (PFR), developed at the Helmholtz Center for Environmental Research (UFZ), is a universal test unit for planted soil filters that reproduces the operational conditions of a constructed wetland (CW) system in laboratory scale. The present research proposes modifications on the PFR original configuration in order to allow its operation in field conditions. A mobile device to obtain undisturbed samples from real-scale HSSFCW was also developed. The experimental setting is presented with two possible operational configurations. The first allows the removal and replacement of undisturbed samples in the CW bed for laboratory investigations, guaranteeing sample integrity with a mobile device. The second allows the continuous operation of the PFR and undisturbed samples as a fraction of the support media, reproducing the same environmental conditions outside the real-scale system. Investigations on the hydrodynamics of the adapted PFR were carried out with saline tracer tests, validating the proposed adaptation. Six adapted PFR units were installed next to full-scale HSSFCW beds and fed with interstitial liquid pumped from two regions of planted and unplanted support media. Fourteen points were monitored along the system, covering carbon fractions, nitrogen and sulfate. The results indicate the method as a promising tool for investigations on CW support media, rhizosphere and open space for studies on CW modeling, respirometry, kinetic parameters, microbial communities, redox potential and plant influence on HSSFCW.
Os processos de tratamento de esgotos sanitários emitem, em maior ou menor grau, gases de efeito estufa. No Brasil, a expressiva maioria da população de municípios de pequeno e médio portes que é atendida pelos serviços de esgotamento sanitário têm seus esgotos tratados por processos anaeróbios, cujo potencial de geração de metano pode ser até 80 vezes superior àquele associado aos processos aeróbios. Diante da realidade demográfica, geográfica e socioeconômica das cidades brasileiras, e sob o contexto de transição para uma economia de baixo carbono, os wetlands construídos (WC) despontam como importante alternativa tecnológica de tratamento de esgotos para municípios de até 20.000 habitantes. À luz dos guias de inventário de efeito estufa do Intergovernmental Panel on Climate Change – IPCC, o presente estudo objetivou analisar, em termos de redução de emissões de metano, o impacto da inserção dos WC na matriz brasileira de tecnologias de tratamento de esgotos. Considerando a projeção de universalização dos serviços de saneamento, as emissões de metano provenientes do tratamento de esgotos sanitários foram estimadas para três diferentes cenários de matriz tecnológica, variando o grau de participação dos WC. O cenário controle representa a manutenção das práticas de tratamento de esgoto conduzidas atualmente, e foi considerado como linha de base para o cálculo das reduções de emissão de metano nos demais cenários avaliados. Os resultados indicaram que, ao reduzir percentualmente a participação dos processos anaeróbios, a incorporação dos WC na matriz de tecnologias de saneamento no Brasil poderia reduzir as emissões totais de metano provenientes do tratamento de esgotos sanitários em mais de 10%, valor que representa cerca de 867 milhões de toneladas de gás carbônico equivalente que deixam de ser emitidas anualmente. Ao serem transformadas em créditos de carbono, esta redução representa uma receita média de cerca de 35 milhões de dólares ao ano.
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