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.
This work assessed the impact of the redox mediator sodium anthraquinone-2,6-disulphonate (AQDS) on the reductive decolourisation of the azo dye Reactive Red 2 (RR2) in one- and two-stage anaerobic systems (R(1) and R(2), respectively). The two-stage system achieved better colour removal efficiencies (52-62%) than the single-stage system (23-33%) in the absence of AQDS. Addition of AQDS accelerated the electrons transfer from the substrate (ethanol) to the dye, which increased the colour removal efficiency of both anaerobic systems (≈ 85%). Finally, the impact of acidogenic and methanogenic phases separation was masked by AQDS supplementation.
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.
This study aimed to evaluate different air dosing strategies such as microaeration flow rates and air dosing points to enhance HS removal in microaerobic systems treating low-strength wastewaters. Efficiency and stability of the reactors, as well as biogas quality, were assessed, and microbial community changes were evaluated using the PCR-DGGE technique. The results showed that the air dosing point affected the HS concentration and that air dosing at the headspace promoted the highest HS removal efficiency. The airflow rate also affected the process, since HS concentration in the biogas was higher at 0.1 mL air.min than at 0.3 mL air.min. The methane concentration in the biogas was also affected by both air dosing point and flow rate, since the lowest value was observed at the highest airflow rate of the headspace dosing point, due to dilution by the N influx applied to the system. The highest productivity and operational efficiency were observed at this air dosing point, with this airflow (HD), which corroborates with the operational results and the ecological parameters, since the microaeration at this stage promoted high bacterial and archaeal species richness and diversity, optimum functional organization, high COD and HS removal efficiencies.
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