Enhanced azo dye Reactive Red 2 degradation in anaerobic reactors by dosing conductive material of ferroferric oxide.

Effect of dosing ferroferric oxide (Fe ₃ O ₄ ) on the anaerobic treatment of azo dye Reactive Red 2 (RR2) was investigated in two anaerobic sequencing batch reactors (ASBRs). System performance, dye degradation pathways, and microbial activities and structure were examined. The addition of Fe ₃ O ₄ significantly improved treatment efficiency, with the removal efficiency of RR2 increased by 116%, the maximum methane (CH ₄ ) yield potential and the peak CH ₄ production rate improved by 7.7% and 22.3%, and the lag phase shortened by 39.6%, respectively. The activity of the electron transport system was significantly enhanced by dosing Fe ₃ O ₄ , with the maximum value increased by 77% and conductivity of the anaerobic sludge increased by 178%. According to the proposed pathway for the degradation of RR2, the degradation products from complete cleavage of the NN bond in RR2 were obtained at the presence of Fe ₃ O ₄ , while were absent without Fe ₃ O ₄ . At high initial dye concentrations, the dosage of Fe ₃ O ₄ alleviated the inhibition to microbes by RR2, and high degradation rate and removal efficiency were maintained. The microbial community structure changed during the long-term acclimation with the dosage of Fe ₃ O ₄ . Paludibacter, Trichococcus and Methanosarcina were predominant and their relative abundances increased with the addition of Fe ₃ O ₄ .
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