Effect of Anaerobic Azo Dye Reduction on Continuous Sludge Digestion

Abstract

Effect of continuous feeding of a reactive azo dye, reactive orange 107, and its hydrolyzed form (HRO107), on a conventional anaerobic digester was investigated in this study together with observation of change in microbial community. Laboratory‐scale digesters were fed with waste activated sludge and azo dye for 575 days continuously. The influent concentrations of reactive azo dye were between 200 and 3200 mg/L. The digester performance was not adversely affected by azo dye and its reduction metabolites throughout the study. A HRO107 concentration with 3200 mg/L was not inhibitory for the digester performance after prolonged exposure. The dye removal efficiencies were between 95 and 99% most of the time of operation implying that dye removal efficiency was not affected by variations in organic loading rate or influent dye concentration. Sulfate‐reducing bacteria may increase in the digester but did not cause any toxicity due to hydrogen sulfide formation after prolonged feeding.