DETOXIFICATION AND PARTIAL MINERALIZATION OF THE AZO-DYE MORDANT ORANGE-1 IN A CONTINUOUS UPFLOW ANAEROBIC SLUDGE-BLANKET REACTOR

In batch toxicity assays, azo dye compounds were found to be many time s more toxic than their cleavage products (aromatic amines) towards me thanogenic activity in anaerobic granular sludge. Considering the abil ity of anaerobic microorganisms to reduce azo groups, detoxication of azo compounds towards methanogens can be expected to occur during anae robic wastewater treatment. In order to test this hypothesis, the anae robic degradation of one azo dye compound, Mordant orange 1 (MO1), by granular sludge was investigated in three separate continuous upflow a naerobic sludge-blanket reactors. One reactor, receiving no cosubstrat e, failed after 50 days presumably because of a lack of reducing equiv alents. However, the two reactors receiving either glucose or a volati le fatty acids (acetate, propionate, butyrate) mixture, could eliminat e the dye during operation for 217 days. The azo dye was reductively c leaved to less toxic aromatic amines (1,4-phenylenediamine and 5-amino salicylic acid) making the treatment of MO1 feasible at influent conce ntrations that were over 25 times higher than their 50% inhibitory con centrations. In the reactor receiving glucose as cosubstrate, 5-aminos alicylic acid could only be detected at trace levels in the effluent a fter day 189 of operation. Batch biodegradability assays with the slud ge sampled from this reactor confirmed the mineralization of 5-aminosa licylic acid to methane.