Development of integrated anaerobic-aerobic bioreactors for the complete degradation of synthetic wastewater containing mono and diazo dye
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Dyes are carcinogenic and mutagenic nature. Eco-friendly, economical and not producing secondary pollutants are the merits of the biological treatment for azo dye than other methods. Purely anaerobic or aerobic treatment and combined treatments were not successful to attain the simultaneous removal of color and intermediates in most of the cases. Apparently, still there is a need to develop the bioreactors to perform complete removal of azo dye including color and intermediates. The present study aimed to develop the bioreactor which able to perform in effective color and intermediates removal of azo dye. The study conducted one anaerobic and three different integrated anaerobic-aerobic bioreactors namely, Upflow Anaerobic Sludge Blanket (UASB) reactor, Integrated Anaerobic-Aerobic Coconut Fiber (IAACF) reactor, Integrated Anaerobic-Aerobic Gravel and Coconut Fiber (IAAGCF) reactor and Integrated Anaerobic-Aerobic Granular Activated Carbon (IAAGAC) reactor. Performance of the above all reactors against the degradation of synthetic wastewater containing mono azo dye Methyl Orange (MO) and diazo dye Reactive Red 120 (RR120) were assessed in different influent color concentrations. . The color removals of MO in UASB reactor were 94%, 90% and 96% in phase 1A, 2A and 3A respectively. The color removals of MO in IAACF reactor were 97%, 96%, 97%, 97% and 96% in phase 1B to 5B, respectively. The intermediates of MO was not removed in UASB reactor and partially removed in other reactors. Symmetric cleavage of this azo bond in MO tends to the formation of the N,N-dimethyl pphenylenediamine and 4-amino sulfonic acid as intermediates. GC-MS analysis resulted the presence of N,N-dimethyl p-phenylenediamine in the effluent. The color removal of MO in IAAGAC and IAAGAC reactors were nearly 98% and 100%, respectively in all phases. The intermediates of MO were completely removed in IAAGAC reactor with increased operation time. The color removals of RR120 in UASB reactor with increased influent cosubstrate were 67%, 76% and 80% in phase IA, IIA and IIIA, respectively. In IAACF reactor, the color removals of RR120 were 87%, 88% and 86% in phase IB, IIB and IIIB, respectively. The color removal of RR120 in IAAGCF and IAAGAC reactors were more than 90% in all the phases. The cleavage of azo bonds in RR120 leads to the formation of sulfonated aromatic compounds as intermediates. The complete removal of RR120 intermediates were noted in IAAGAC reactor with increased operation time. The results of present study revealed that the highly reductive anaerobic environment suited for effective color removal of MO and RR120 rather than intermediates removal. Partial mineralization of MO and RR120 intermediates was observed in integrated anaerobic-aerobic system. Complete removal of MO and RR120 intermediates was possible in integrated anaerobicaerobic system with suitable biomaterials like granular activated carbon. The variation of kinetic constants in kinetic study revealed that the performance of color and COD removal was in decreasing trend with respect to increased color influent in both MO and RR120. However the performance was decreasing, effective color removal was observed in the reasonable color influents range (100 to 1000mg/L).