LAUSR

In this study, two treatment routes were investigated for degradation of the azo dye Reactive Orange 16 (RO16): biodegradation in an anaerobic MBBR (R1) and ozonation followed by biological treatment in an aerobic MBBR (R2). Along with the dye, glucose and nutrients were supplemented to the influent fed to R1 as carbon co-substrate and nitrogen source, respectively. In R1, maximum color removal of 61 ± 18% was achieved for 5 mg l −1 of dye, hydraulic retention time of 12 h and influent COD of 800 mg l −1 . Moreover, RO16 biodegradation was limited by carbon source (glucose) and attached solids concentrations. Batch tests revealed that anaerobic biodegradation of the dye and glucose followed second-order kinetics and RO16 degradation constant increased as the initial COD was reduced. Considering the relatively low color removal achieved anaerobically, dye solutions (100 to 500 mg l −1 ) were ozonated, enabling fast discoloration of at least 97% within 20 min for the highest dye concentration. However, the low COD (50–75%) and TOC (35–40%) removals achieved indicate that only partial mineralization occurred. RO16 (500 mg l −1 ) ozonation products were identified, and a degradation pathway was proposed. Subsequently, the ozonated solutions were supplemented with glucose and nutrients and fed to R2. COD removal decreased considerably (from 92 to 81%) when ozonated solutions with original dye concentration of 500 mg l −1 were fed to R2, but ammonium removal remained fairly stable. Three compounds identified before biological treatment were not found in R2 effluent, suggesting that they were biodegraded.