Potencial de nitrificação/desnitrificação de tanque séptico e wetland construído com recirculação no tratamento descentralizado de esgoto de empreendimento habitacional / Nitrification/denitrification potential of a septic tank and a constructed wetland with recirculation in the decentralized wastewater treatment from a housing development

RESUMO Os wetlands construídos (WC) são uma ecotecnologia aplicável para o tratamento descentralizado de esgotos notadamente em pequenas comunidades, em razão de sua simplicidade operacional. Existem vários arranjos e combinações de WC possíveis, destacando-se o arranjo tanque séptico (TS), seguido da modalidade de WC de escoamento vertical (WCV) com recirculação do efluente do WCV de volta para o TS, como proposta para possibilitar a remoção de nitrogênio presente no esgoto afluente. Entretanto, no Brasil, essa configuração e suas implicações operacionais e de desempenho são pouco exploradas. Diante disso, o objetivo deste trabalho foi avaliar o desempenho de um sistema de TS seguido de um WCV com recirculação no tratamento descentralizado de esgoto doméstico. O sistema empregado no tratamento de esgoto de um equivalente populacional de dez habitantes é composto de um TS (4,7 m3 de volume útil), seguido de um WCV (24,5 m2 de área superficial) preenchido com brita e plantado com Canna spp. O monitoramento, que compreendeu um período de nove meses, teve início após um ano e cinco meses de operação do sistema. Utilizando taxa de 50% de recirculação, taxa de aplicação hidráulica no WCV de 85 mm d-1 e carga de 47 g DQO m-2.d-1, foram obtidas boas eficiências para remoção conjunta de demanda química de oxigênio — DQO (80%), sólidos em suspensão totais — SST (85%) e nitrogênio total —NT (42%), mesmo com elevadas cargas orgânicas. Além das boas eficiências apresentadas, o sistema demonstrou ser robusto e de operação simples e representa uma alternativa tecnológica com potencial para o tratamento descentralizado de esgotos de empreendimentos habitacionais.

ABSTRACT Constructed wetland (CW) is an applicable eco-technology for decentralized wastewater treatment, notably in small communities, due to its operational simplicity. CW has several possible arrangements and combinations, among which the septic tank (ST) stands out, followed by the vertical flow constructed wetland (VFCW), with treated effluent recirculation back to the ST to enable nitrogen removal. However, in Brazil, this configuration and its operational and performance implications are little explored. Therefore, this study aimed to evaluate the performance of an ST system, followed by a VFCW with recirculation in the decentralized treatment of domestic wastewater. The wastewater treatment system for 10 inhabitants consists of an ST (4.7 m3 of useful volume), followed by a VFCW (24.5 m2 of surface area) planted with Canna spp. The monitoring, which covered a period of nine months, started after one year and five months of system operation. Using a 50% recirculation rate, VFCW hydraulic loading rate of 85 mm d-1, and organic load of 47 g COD m-2 d-1, good efficiencies were obtained for the joint removal of chemical oxygen demand — COD (80%), total suspended solids — TSS (85%), and total nitrogen — TN (42%), even with high organic loads. In addition to the good efficiencies presented, the system proved to be robust and easy to operate, representing a technological alternative with potential for the decentralized wastewater treatment of housing developments.

Feeding mode influence on treatment performance of unsaturated and partially saturated vertical flow constructed wetland.

This study aimed to evaluate the influence of two different feeding modes on wastewater treatment performance and oxygen consumption rate (OCR) of the unsaturated (UVF wetland) and partially saturated (SVF wetland) vertical flow constructed wetlands operated in parallel under subtropical climate for four years. Each wetland had a superficial area of 7.5 m2 and was planted with Typha domingensis. Both units have a filter media depth of 0.75 m, composed by sand (effective diameter of 0.29 mm and uniformity of 4). UVF wetland operated typically unsaturated, while SVF wetland had the bottom part saturated (57% of total depth). Two feeding modes were evaluated for both wetlands. The feeding mode was operated within the limits recommended by the German standard, with a hydraulic loading rate (HLR) of 75 mm d-1 and specific pulse volume (SPV) of 19 L m-2 for both wetlands and a specific hydraulic loading rate (SHLR) of 8 and 9 L m-2 min-1 for UVF and SVF wetlands, respectively. Meanwhile, the second feeding mode was applied for both wetlands, being an HLR of 103 mm d-1, 26 L m-2 of SPV, and 4 L m-2 min-1 of SHLR. The load removal efficiency of SVF wetland was higher than the UVF wetland for all parameters and feeding modes. No statistical difference was identified for OCR values between wetlands and feeding mode. The results showed that operating UVF and SVF wetlands with a SHLR around 4 L m-2 min-1 and SPV equal of 26 L m-2 is preferable. This fact could represent a significant reduction in inlet pumping power requirements and also less superficial area requirements.

Influence of the flooded time on the performance of a tidal flow constructed wetland treating urban stream water.

A vertical subsuperficial tidal flow constructed wetland (TFCW) operated under flooded time (FT) variation, was evaluated in the removal of carbonaceous, nitrogenous, and phosphorous matter from urban stream water. The TFCW downflow (117 L) was filled with bricks (44% porosity) and vegetated with Althernanthera philoxeroides (32 plants m-2). The TFCW was operated under different flooded times - Stage A (48 h), B (36 h), C (24 h), and D (12 h), organic loading rates of 19.58-43.83 gCOD m-2 d-1, 3.68-6.94 gTN m-2 d-1 and 0.93-2.00 gTP m-2 d-1 and volumetric load rates of 46.8, 58.5, 78.0 and 11.7 L d-1. No significant differences were observed in the removal efficiencies to Chemical Oxygen Demand (COD 66 to 94%), Total Ammonia Nitrogen (TAN 58 to 87%), and Total Nitrogen (TN 53 to 78%) among the stages, and nitrate concentrations lower than 6 mg L-1 in the effluent. High Total Phosphorus removal was obtained in FT of 48 h (TP 79%). Total phosphorus loading rate was a limiting factor in TP removal, which reduced along with the reduction of FT. The nitrifying community was present over time since ammonia-oxidizing bacteria (Nitrosospira) and nitrite-oxidizing bacteria (Nitrobacter and Nitrospira) were identified in operational stages with variation in relative abundance, but TAN removal efficiency did not show significant differences. There was no change in the denitrifying community structure, indicating that FT did not influence the TN removal. A. philoxeroides was responsible for phytoextraction of 2.1% of TN and 2.7% of TP from the total removed by TFCW. TN removal (65%) was attributed to adsorption in the filtering material and microbial metabolism during the rest time. The findings of this study suggest FT of 12 h to remove COD and TN, and equal to or higher than 48 h to remove TP.

Incorporação de nitrogênio e fósforo no tecido foliar da macrófita Typha domingensis Pers. durante o tratamento de efluente da bovinocultura leiteira em wetlands construídos / Incorporation of nitrogen and phosphorus in the leaves of Typha domingensis Pers. macrophyte during treat dairy cattle wastewater in constructed wetlands

RESUMO O objetivo deste estudo foi avaliar o desempenho da macrófita Typha domingensis Pers., em diferentes etapas de seu desenvolvimento, na remoção de nitrogênio (N) e fósforo (P) em um wetland construído horizontal (WCH) aplicado no tratamento de efluente de bovinocultura leiteira. Para isso, foi realizado o monitoramento do crescimento e dos teores de N e P no tecido foliar das macrófitas, durante um período de 120 dias de crescimento. A macrófita Typha domingensis Pers. foi responsável por uma remoção média de 5,12 e 3,16% das cargas de N e P aplicadas no WCH, respectivamente. As maiores taxas de remoções de nutrientes (30,2 e 6,4 g P kg-1) foram identificadas quando ocorreram as maiores taxas de crescimento foliar (24,17 cm semana-1).

ABSTRACT The objective of this study was to evaluate the performance of macrophyte Typha domingensis Pers. in different development stages in the nitrogen and phosphorus removal from a horizontal flow constructed wetland (WCH) applied for dairy cattle wastewater treatment. In this way, growth, nitrogen and phosphorus levels in the leaf tissue of macrophytes were monitored during a 120-day growth period. Typha domingensis Pers. macrophyte was responsible for a mean removal of 5.12 and 3.16% of the applied loads in the WCH, for nitrogen and phosphorus, respectively. The higher nutriens removal rates (30.2 and 6.4 g P kg-1) were identified when the higher tissue growth rates occurred (24.17 cm week-1).

Effects of partially saturated conditions on the metabolically active microbiome and on nitrogen removal in vertical subsurface flow constructed wetlands.

Nitrogen dynamics and its association to metabolically active microbial populations were assessed in two vertical subsurface vertical flow (VF) wetlands treating urban wastewater. These VF wetlands were operated in parallel with unsaturated (UVF) and partially saturated (SVF) configurations. The SVF wetland exhibited almost 2-fold higher total nitrogen removal rate (5 g TN m-2 d-1) in relation to the UVF wetland (3 g TN m-2 d-1), as well as a low NOx-N accumulation (1 mg L-1 vs. 26 mg L-1 in SVF and UVF wetland effluents, respectively). After 6 months of operation, ammonia oxidizing prokaryotes (AOP) and nitrite oxidizing bacteria (NOB) displayed an important role in both wetlands. Oxygen availability and ammonia limiting conditions promoted shifts on the metabolically active nitrifying community within 'nitrification aggregates' of wetland biofilms. Ammonia oxidizing archaea (AOA) and Nitrospira spp. overcame ammonia oxidizing bacteria (AOB) in the oxic layers of both wetlands. Microbial quantitative and diversity assessments revealed a positive correlation between Nitrobacter and AOA, whereas Nitrospira resulted negatively correlated with Nitrobacter and AOB populations. The denitrifying gene expression was enhanced mainly in the bottom layer of the SVF wetland, in concomitance with the depletion of NOx-N from wastewater. Functional gene expression of nitrifying and denitrifying populations combined with the active microbiome diversity brought new insights on the microbial nitrogen-cycling occurring within VF wetland biofilms under different operational conditions.

Unraveling the active microbial populations involved in nitrogen utilization in a vertical subsurface flow constructed wetland treating urban wastewater.

The dynamics of the active microbial populations involved in nitrogen transformation in a vertical subsurface flow constructed wetland (VF) treating urban wastewater was assessed. The wetland (1.5m2) operated under average loads of 130gCODm-2d-1 and 17gTNm-2d-1 in Period I, and 80gCODm-2d-1 and 19gTNm-2d-1 in Period II. The hydraulic loading rate (HLR) was 375mmd-1 and C/N ratio was 2 in both periods. Samples for microbial characterization were collected from the filter medium (top and bottom layers) of the wetland, water influent and effluent at the end of Periods I (Jun-Oct) and II (Nov-Jan). The combination of qPCR and high-throughput sequencing (NGS, MiSeq) assessment at DNA and RNA level of 16S rRNA genes and nitrogen-based functional genes (amoA and nosZ-clade I) revealed that nitrification was associated both with ammonia-oxidizing bacteria (AOB) (Nitrosospira) and ammonia-oxidizing archaea (AOA) (Nitrososphaeraceae), and nitrite-oxidizing bacteria (NOB) such as Nitrobacter. Considering the active abundance (based in amoA transcripts), the AOA population revealed to be more stable than AOB in both periods and depths of the wetland, being less affected by the organic loading rate (OLR). Although denitrifying bacteria (nosZ copies and transcripts) were actively detected in all depths, the denitrification process was low (removal of 2gTNm-2d-1 for both periods) concomitant with NOx-N accumulation in the effluent. Overall, AOA, AOB and denitrifying bacteria (nosZ) were observed to be more active in bottom than in top layer at lower OLR (Period II). A proper design of OLR and HLR seems to be crucial to control the activity of microbial biofilms in VF wetlands on the basis of oxygen, organic-carbon and NOx-N forms, to improve their capacity for total nitrogen removal.

Nitrogen transforming bacteria within a full-scale partially saturated vertical subsurface flow constructed wetland treating urban wastewater.

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 3144m2, 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 (764m2 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 4gCODm-2d-1 and a hydraulic loading rate of 24.5mmd-1. 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 ß-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.

Experiências brasileiras com wetlands construídos aplicados ao tratamento de águas residuárias: parâmetros de projeto para sistemas horizontais / Brazilian experiences with constructed wetlands applied to wastewater treatment: design parameters for horizontal systems

A utilização no Brasil de sistemas tipo wetlands construídos no tratamento de águas residuárias iniciou no ano de 1980, intensificando-se a partir do ano 2000. O objetivo deste trabalho é apresentar um estado da arte da aplicação no Brasil dos wetlands construídos de escoamento subsuperficial de fluxo horizontal (WCFH), identificando parâmetros de projeto e dados operacionais. Aborda-se, inicialmente, uma classificação para os wetlands construídos, seguido dos parâmetros de projeto e operação dos WCFH, destacando os diferentes critérios de dimensionamento, tais como os modelos oriundos da cinética de primeira ordem aplicável aos reatores tipo pistão, a relação de área per capita, o carregamento orgânico superficial e a taxa hidráulica, bem como a composição das unidades de tratamento e as macrófitas empregadas.

The implementation of constructed wetlands for wastewater treatment in Brazil has started in the eighties, being intensified since the year 2000. The aim of this study is to present the state of art of implementation of horizontal sub-superficial flow constructed wetlands (HFCW) in Brazil, focusing on the identification of design parameters and operational data. Initially a classification for constructed wetlands is given, followed by design parameters and operational conditions for HFCW, highlighting different project criteria, e.g. models from first order kinetics for tubular piston reactors, the relation of superficial area per person, the organic superficial loading and the hydraulic loading, as well as the composition of units and macrophytes utilised.

Caracterização da microfauna em estação de tratamento de esgotos do tipo lodos ativados: um instrumento de avaliação e controle do processo / Microfauna characterization in activated sludge wastewater treatment plant: an instrument of assessment and control of process

A microfauna presente em uma ETE por lodos ativados foi caracterizada, correlacionada com parâmetros físico-químicos e utilizada em modelos existentes de avaliação de sistemas. Durante 351 dias o lodo ativado manteve-se estável com flocos compactos, pequenos e com poucos filamentos. Os protozoários predominantes no lodo foram as tecamebas e os ciliados predadores de flocos, indicando estabilidade do sistema. Os métodos propostos em literatura, baseados no IBL, na densidade total da microfauna e na relação entre ciliados predadores de flocos e ciliados fixos, mostraram-se eficientes para o diagnóstico das condições depurativas do sistema. A análise qualitativa do lodo, englobando o tamanho, quantidade de filamentos, compactação e a identificação das espécies dominantes, foi suficiente para uma caracterização imediata das condições depurativas do sistema de tratamento.