The aim of this study was to characterize the nitrogen transforming bacterial communities within a partially saturated vertical subsurface flow constructed wetland (VF) treating urban wastewater in southern Brazil. The VF had a surface area of 3144m, and was divided into four wetland cells, out of which two were operated while the other two rested, alternating cycles of 30days. The nitrifying and denitrifying bacterial communities were characterized in wetland cell 3 (764m surface area) over a period of 12months by using the FISH technique. Samples were collected monthly (from Feb 2014 to Feb 2015) from different layers within the vertical profile, during operation and rest periods, comprising a total of 6 sampling campaigns while the cell was in operation and another 6 when the cell was at rest. This wetland cell operated with an average organic loading rate (OLR) of 4gCODmd and a hydraulic loading rate of 24.5mmd. The rest periods of the wetland cell presented influences on the abundance of ammonia-oxidizing bacteria (AOB) (8% and 3% for feed and rest periods, respectively), and nitrite-oxidizing bacteria (NOB) (5% and 2% for feed and rest periods, respectively). However, there was no influence of the rest periods on the denitrifying bacteria. AOB were only identified in the top layer (AOB β-proteobacteria) in both operational and rest periods. On the other hand, the NOB (Nistrospirae and Nitrospina gracilis) were identified in feed periods just in the top layer and during rest periods just in the intermediate layer. The denitrifying bacteria (Pseudomonas spp. and Thiobacillus denitrificans) were identified from the intermediate layer downwards, and remained stable in both periods. Based on the identified bacterial dynamics, the partially saturated VF wetland operated under low OLR enabled favorable conditions for simultaneous nitrification and denitrification.

Resumoobjetivo deste trabalho é apresentar o desempenho dos wetlands construídos de fluxo vertical (WCFV) submetidos a diferentes carregamentos orgânicos e hidráulicos, a fim de incorporar esta tecnologia como opção no tratamento descentralizado de esgotos em empreendimentos comercial e residencial. Avaliou-se ao longo de dois anos dois sistemas de tratamento: (i) sistema 1 -empreendimento comercial: composto por um Reator Aneróbio Compartimentado (RAC) seguido de WCFV (área superficial total de 189 m²); (ii) sistema 2 -condomínio residencial: composto pela sequência RAC e WCFV com fundo saturado (área superficial total de 3.141 m²). Com o monitoramento operacional e analítico junto aos wetlands, determinaram-se taxas hidráulicas aplicadas variando de 130 a 12 mm.d-1 e carregamentos médios aplicados variando de 87 a 1,9 gDQO m -2 .d -1 para os sistemas 1 e 2, respectivamente. Os distintos carregamentos foram resultantes da demanda atual dos empreendimentos, sendo que os sistemas 1 e 2 apresentaram eficiências médias globais de remoção em termos de concentração de 75% e 93% para DQO, de 88% e 97% para DBO e de 83% e 94% para SS, respectivamente. A partir dos resultados obtidos, recomenda-se a utilização dos WCFV como alternativa tecnológica de tratamento de esgoto sob o contexto da descentralização. 75% and 93% to COD, of 88% and 97% to BOD and of 83% and 94% to SS, respectively. These results lead us to recommend the use of VFCW as a decentralized wastewater treatment technology. Palavras

Utilization of the French system of vertical wetlands for treating raw sewage keeps increasing, but there is still limited consolidated information on their long term use in tropical countries. Under these conditions, there are indications that surface area requirements can decrease, whilst still keeping a satisfactory performance. However, variations in the operational mode and the role of the surface organic deposit layer under warm climatic conditions have not been fully investigated. The goal of this work was to evaluate the performance of a system comprised of only the first stage of the French system, with a further reduction of 1/3 of the area (utilization of only two units in parallel, instead of three) in terms of organic matter removal and nitrogen conversion, with one unit with a deposit layer accumulated over 9 years of operation, and the other unit without sludge layer, under Brazilian tropical conditions. The system was originally designed according to Cemagref/Irstea recommendations for the first-stage of the French system for the treatment of raw sewage generated by an equivalent population of 100 inhabitants. However, it was later on changed, and operated with only two units, using only 0.6 m2·pe−1. Feeding and resting periods were of 7 days each. In order to evaluate the influence of the sludge layer, the top sludge from one of the units was removed, and the performance of both units was compared by the Mann-Whitney test. The database comprises the wetland performance values in terms of dissolved oxygen (DO), redox potential (Eh), chemical oxygen demand (COD), biochemical oxygen demand (BOD), total suspended solids (TSS), total Kjeldahl nitrogen (TKN), NH4+-N and NO3+-N, covering a monitoring period of 15 months. The effluent DO concentrations were significantly lower in the unit with top sludge, but still sufficiently high in both units. Although there were some variations between both units, effluent concentrations of the major pollutants were not significantly different in the units with and without sludge, and removal efficiencies based on mean values were considered good, given the reduced area of the system: BOD (80% and 79%), TSS (85% and 82%), TKN (60% and 63%) for the units with and without sludge, respectively. Under Brazilian climatic conditions, with the reduced area and employing longer feeding cycles (7 days), the sludge accumulation rate (less than 1 cm·year−1) was lower compared to the French mean values.

Os sistemas wetlands construídos são uma ecotecnologia de tratamento de águas residuárias enquadrados como soluções baseadas na natureza. Inúmeros elementos físicos e biológicos – em destaque os materiais filtrantes, as macrófitas e os microrganismos – atuam em consonância nas remoções da matéria orgânica suspensa e dissolvida presentes nos afluentes submetidos ao tratamento, bem como, nas transformações dos nutrientes presentes. Os wetlands construídos compõem inúmeros arranjos tecnológicos de tratamento de esgotos, são consolidados no mundo e no Brasil como mais uma opção para o controle da poluição hídrica. Inúmeras empresas, operadoras de saneamento, universidades e centros de pesquisa vêm aplicando e estudando as diversas modalidades de wetlands construídos. O Grupo Wetlands Brasil, o qual congrega inúmeros pesquisadores e praticantes distribuídos em todo o território nacional, foi estabelecido há uma década tendo como premissa a disseminação da utilização desta ecotecnologia na busca da universalização do esgotamento sanitário.

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