Correlation of anaerobic biodegradability and the electrochemical characteristic of azo dyes

Some experiments were conducted to study some electrochemical factors affecting the bacterial reduction (cleavage) of azo dyes, knowledge of which will be useful in the wastewater treatments of azo dyes. A common mixed culture was used as a test organism and the reductions of Acid Yellow 4, 11, 17 and Acid Yellow BIS were studied. It was found that the azo dyes were reduced at different rates, which could be correlated with the reduction potential of the azo compounds in cyclic voltammetric experiments. Acid Yellow BIS (E-r =616.75 mV) was reduced at the highest rate of 0.0284 mol g dry cell weight(-1) h(-1), Acid Yellow 11 (E (r)=593.25 mV) at 0.0245 mol g dry cell weight(-1) h(-1) and Acid Yellow 4 (E (r)=513 mV) at 0.0178 mol g dry cell weight(-1) h(-1). At the same time, the decolourization rate of Acid Yellow 17 (E-r=627.5 mV) was 0.0238 mol g dry cell weight(-1) h(-1), which was affected by the nature of chlorine substituent. Reduction of these azo dyes did not occur under aeration conditions. These studies with a common mixed culture indicate that the reduction of azo dyes may be influenced by the chemical nature of the azo compound. The reduction potential is a preliminary tool to predict the decolourization capacity of oxidative and reductive biocatalysts.