Tratamento de efluentes urbanos e recuperação de energia através de sistema integrado composto por reator anaeróbio, microalgas e wetland construído de fluxo vertical

O presente trabalho teve como objetivo propor um sistema integrado de tratamento de efluentes urbanos composto por reator anaeróbio, microalgas autóctones e wetland construído de fluxo vertical, com macrófita nativa do Sul do Brasil, além de recuperar energia através da biomassa gerada durante o processo. A pesquisa foi desenvolvida junto a estação de tratamento de águas residuais da Universidade de Santa Cruz do Sul (ETE/UNISC). Foi proposto um sistema integrado composto por reator anaeróbico (RA), microalgas (MA) e wetland construído de fluxo vertical (WCFV) para tratamento das águas residuais produzidas no campus da Universidade com tempo total de detenção hidráulica (TDH) de 17 dias. O sistema integrado foi configurado para proliferação de microalgas, a partir de efluente pós-tanque equalizador da ETE e com polimento final através de wetland construído, tendo como partida a configuração do fotobioreator sem inoculação de cepas selvagens ou comerciais de microalgas e com a utilização da espécie de macrófita emergente Hymenachne grumosa no WCFV. Os resultados obtidos demonstraram que o sistema integrado (RA, MA e WCFV) apresenta bom desempenho na redução de COD; DBO5 e Fósforo Total (63,22%; 61,18% e 53,91%, respectivamente), além de taxas de remoção de Nitrogênio Amoniacal (N-NH3); Coliformes totais e Escherichia colide99,98%; 99,99% e 100%, respectivamente. A obtenção das amostras de biomassa algácea para produção de biogás foi realizada através de separação e coleta das microalgas com período de TDH de 14 dias, enquanto a biomassa referente às macrófitas utilizadas no wetland construído foi realizada a cada 6 meses. A conversão da biomassa das microalgas em biogás foi em média de 2322,51NmL-gSV-1com CH4de 54,61% (inverno/2019); de 4491,47 NmL-gSV-1com CH4de 57,17% (primavera/2019 e com geração de biogás de 3826,70NmL-gSV-1 com CH4 de 44,26% para biomassa wetland construído inverno e primavera/2019. Em relação à redução da genotoxicidade, observou-se que o sistema integrado (WCFV) foi eficiente, uma vez que apresentou uma redução significativa (p<0,001) na frequência de micronúcleos (MN) e aberrações cromossômicas (CA) quando comparado com o sistema convencional de tratamento (ETE). Ainda, foi desenvolvido um separador de biomassa microalgal de baixo custo, sem aporte energético com depósito de patente junto ao Instituto Nacional de propriedade Intelectual (INPI). Assim, os resultados do estudo destacam a relevância na proposição do sistema integrado como alternativa de tecnologia sustentável aplicada ao tratamento de águas residuais, uma vez que, além de tratar o efluente de modo eficiente, também demonstrou potencial geração de energia, reforçando o conceito de sustentabilidade no saneamento ambiental.The present work aimed at to propose an integrated system for the treatment of urban wastewaters besides recovering energy through the biomass generated during the process. The system was composed of an anaerobic reactor (AR), autochthonous microalgae (MA) and vertical flow constructed wetlands (VFCW) vegetated with native macrophyte of the South of Brazil with full hydraulic detention time (HDT) of 17 days. The research was carried out at the wastewater treatment plant (WWTP) of the University of Santa Cruz do Sul (ETE/UNISC). The integrated system was configured for MA proliferation, from wastewaters arising from the equalizer tank of WWTP and with final polishing byVFCW, starting with the configuration of the photobioreactor without inoculation of wild or commercial strains of MA and with the use of emerging macrophyte species Hymenachne grumosain VFCW. The results obtained showed that the integrated system (RA, MA and WCFV) reduced COD, BOD5and Total Phosphorus by 63.22%; 61.18% and 53.91%, respectively, besides achieving good removal rates for Ammoniacal Nitrogen (N-NH3) Total coliforms and 99.98% Escherichia coli; 99.99% and 100%, respectively. The collection of algal biomass samples for biogas production was performed by separating and collecting the microalgae with a HDT of 14 days, while the biomass referring to the macrophytes used in the VFCW was carried out every 6 months. The conversion of MA biomass into biogas averaged 2322.51 NmL-gSV-1with 54.61% CH4(winter/2019); 4491.47 NmL-gSV-1with 57.17% CH4(spring/2019) and with biogas generation of 3826.70 NmL-gSV-1with 44.26% CH4for VFCW biomass winter and spring/ 2019. Regarding the reduction of genotoxicity, it was observed that the integrated system was efficient, as it presented a significant reduction (p<0.001) in the frequency of micronuclei (MN) and chromosomal aberrations (CA) when compared to the treatment of the WWTP. Furthermore, a low-cost, energy-free, microalgal biomass separator was developed with a patent deposit at the National Institute of Intellectual Property (INPI). Thus, the results obtained in the present study highlight the relevance of proposing the integrated system as an alternative of sustainable technology applied to the treatment of wastewaters, since, in addition to treating the wastewaters in an efficient manner, it also demonstrated potential for energy generation, reinforcing the concept of sustainability in environmental sanitation

Hybrid constructed wetlands integrated with microbial fuel cells and reactive bed filter for wastewater treatment and bioelectricity generation

The present study aimed to develop a pilot-scale integrated system composed of anaerobic biofilter (AF), a floating treatment wetland (FTW) unit, and a vertical flow constructed wetland coupled with a microbial fuel cell (CW-MFC) and a reactive bed filter (RBF) for simultaneously decentralized urban wastewater treatment and bioelectricity generation. The first treatment stage (AF) had 1450 L and two compartments: a settler and a second one filled with plastic conduits. The two CWs (1000 L each) were vegetated with mixed plant species, the first supported in a buoyant expanded polyethylene foam and the second (CW-MFC) filled with pebbles and gravel, whereas the RBF unit was filled with P adsorbent material (light expanded clay aggregate, or LECA) and sand. In the CW-MFC units, 4 pairs of electrode chambers were placed in different spacing. First, both cathode and anode electrodes were composed of graphite sticks and monitored as open circuit. Later, the cathode electrodes were replaced by granular activated carbon (GAC) and monitored as open and closed circuits. The combined system efficiently reduced COD (> 64.65%), BOD₅(81.95%), N-NH₃(93.17%), TP (86.93%), turbidity (94.3%), and total coliforms (removal of three log units). Concerning bioenergy, highest voltage values were obtained with GAC electrodes, reaching up to 557 mV (open circuit) and considerably lower voltage outputs with closed circuit (23.1 mV). Maximum power densities were obtained with 20 cm (0.325 mW/m²) and 30 cm (0.251 mW/m2). Besides the electrode superficial areas, the HRT and the water level may have influenced the voltage values, impacting DO and COD concentrations in the wastewater