Degradation of a monoazo dye Alizarin Yellow GG in aqueous solutions by gamma irradiation: Decolorization and biodegradability enhancement

The irradiation-induced degradation of an azo dye, Alizarin Yellow GG (AY-GG), was investigated in aqueous solution under gamma irradiation using a 60Cobalt source at a dose rate of 113 Gy/min. The decolorization percentage of AY-GG reached 65% when its initial concentration was 100 mg/l and the absorbed dose was 9 kGy. The decolorization process could be described by first-order kinetic equation. In addition, specific oxygen uptake rate (SOUR, mg O2 (g MLVSS)−1 h−1) of activated sludge using the irradiated azo dye solutions was 8.1 mg O2 (g MLVSS)−1 h−1 after 9 kGy irradiation, indicating that the biodegradability of AY-GG could be enhanced by 30%. However, toxic intermediates including heterocyclic aromatic amines and cyanides were detected during the irradiation process, which inhibited the complete biological degradation of azo dye. Fortunately, the inhibition could be eliminated by further irradiation. The azo dye solution became amenable to biodegradation and can be further treated by biological treatment process.

► Decolorization process by radiation conformed to first-order kinetics.
► Biodegradability of AY-GG could be enhanced 30% after 9 kGy radiation.
► Radiation can be used as a pretreatment technology for azo dye-containing wastewater.
► Combining radiation with aerobic biological treatment is a feasible strategy.