AbstractThe reductive transformation of azobenzene and selected derivatives was investigated in anaerobic sediment/water systems. The azo compounds exhibited pseudo‐first‐order disappearance kinetics through at least three half‐lives. The reduction kinetics of these compounds was studied as a function of their reduction potential and sediment/water distribution coefficient. There was no apparent correlation between the observed disappearance rate constant and reduction potential. In general, as the distribution coefficient increased, the rate of reduction decreased. Values for the pseudo‐first‐order rate constant for disappearance ranged from 5.11 × 10−3min−1for methyl red to 6.03 × 10−6min−1for 4,4′‐dichloroazobenzene. Removal of the solid phase from the sediment/water samples gave a filtrate with little or no reactivity. Chemical sterilization of the sediment/water sample with formaldehyde and treatment withm‐cresol, a dehydrogenase inhibitor, or sodium azide, a metabolic inhibitor, had little effect on the observed reduction rate constants for azobenzene, indicating an abiotic reduction process. Heat sterilization indicated that the reducing agent was heat labile. In studies with 4,4′‐dimethoxyazobenzene, the observed rate constant for reduction increased with increasing sediment concentration. Based on the results of these studies, a model for the reduction process was developed that incorporates a nonreactive sorptive sink and a reactive site, both of which are
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