RESUMO
RESUMO Nesta pesquisa, estudou-se o desempenho de três filtros biológicos anaeróbios com novos e diferentes meios de suporte em tempos de detenção hidráulica (TDH) distintos (5,5 e 11,1 horas), objetivando a remoção de algas de efluentes de lagoas de estabilização. O considerável desempenho no pós-tratamento (remoções de até 77,4%) pode ser atribuído à atuação dos mecanismos de sedimentação, retenção física e assimilação biológica. Foi desenvolvido um modelo de decaimento para clorofila com base na simplificação da equação de transporte de massa. O coeficiente global de decaimento foi descrito como uma função dos números de Reynolds e Weber, obtida por meio de ajuste aos dados experimentais com um coeficiente de determinação superior a 0,96. Para confirmação de que a função de Reynolds e Weber descreve bem o comportamento de k, foram realizadas simulações do impacto das seguintes variáveis na eficiência de remoção de algas: comprimento do filtro (altura do leito), diâmetro do filtro, diâmetro do meio suporte, porosidade, vazão, tensão superficial e da viscosidade do líquido. As simulações desenvolvidas demonstraram coerência nos resultados, reforçando que os números de Reynolds e Weber, assim como o modelo de fluxo em pistão, podem ser usados para descrever o processo de remoção de algas em filtros anaeróbios.
ABSTRACT In this research we studied the performance of three anaerobic biological filters with new and different support media in different hydraulic retention time (HRT): 5.5 and 11.1 hours, aiming at the removal of wastewater stabilization ponds of algae. The considerable performance in the post-treatment (removal of up to 77.4%) can be attributed to the actions of sedimentation mechanisms, physical restraint and biological assimilation. It has developed a model for chlorophyll decay from the simplification of mass transport equation. The overall decay coefficient was described as a function of Reynolds and Weber numbers, which was obtained through adjusting the experimental data with a determination coefficient greater than 0.96. To confirm that the Reynolds and Weber function describes well the k behavior, simulations were made of the impact of these variables on algae removal efficiency: filter length (bed height), filter diameter, the diameter of the support means, porosity, flow, surface tension and viscosity of the liquid. Simulations show consistency in the results, reinforcing that the Reynolds and Weber numbers and the flow model of piston may be used to describe the process of removing algae in anaerobic filters.
RESUMO
Colour and COD removals of the azo dyes Congo Red (CR) and Reactive Black 5 (RB5) were individually evaluated in a sequential anaerobic/aerobic treatment system. Additionally, dye toxicity was assessed by using acute ecotoxicity tests with Daphnia magna as the indicator-organism. The anaerobic reactor was operated at approximately 27 °C and with hydraulic retention times of 12 and 24 h. The aerobic reactor was operated in batch mode with a total cycle of 24 h. During anaerobic step, high colour removals were obtained, 96.3% for CR (400 mg/L) and 75% for RB5 (200 mg/L). During the aerobic phase, COD effluent was considerably reduced, with an average removal efficiency of 52% for CR and 85% for RB5, which resulted in an overall COD removal of 88% for both dyes. Ecotoxicity tests with CR revealed that the anaerobic effluent presented a higher toxicity compared with the influent, and an aerobic post-treatment was not efficient in reducing toxicity. However, the results with RB5 showed that both anaerobic and aerobic steps could decrease dye toxicity, especially the aerobic phase, which removed completely the toxicity in D. magna. Therefore, the anaerobic/aerobic treatment is not always effective in detoxifying dye-containing wastewaters, sometimes even increasing dye toxicity.
