Degradation of azo dye Mordant Yellow 10 in a sequential anaerobic and bioaugmented aerobic bioreactor

Complete biodegradation of azo dyes requires an anaerobic and aerobic step, in the anaerobic step sulfonated azo dyes (SADs) are reduced, yielding (su lfonated) aromatic amines ((S)AAs) which can be degraded aerobically. The c omplete biodegradation of the SAD Mordant Yellow 10 (MY10) was studied in a sequential anaerobic and aerobic bioreactor. Anaerobically, MY10 was reduc tively cleaved and the resulting aromatic amines, 5-aminosalicylic acid (5- ASA) and sulfanilic acid (SA), were both recovered in high stoichiometric y ields. One of the AAs, 5-ASA, was readily degraded under aerobic conditions . However, SA was not degraded aerobically in the continuous experiment bec ause no SA-degrading bacterial activity was present in the system. Therefor e, a SA-degrading enrichment culture derived from Rhine sediment was used a s an inoculum source. This enrichment culture was bioaugmented into the aer obic reactor by increasing the hydraulic retention time (HRT), thus enablin g SA-degrading activity to develop and maintain in the aerobic reactor. Aft er decreasing the HRT, the SA-degrading activity remained in the bioreactor and the stoichiometric recovery of sulfate (a SA biodegradation product) i ndicated the mineralization of SA after bioaugmentation. Batch experiments with aerobic reactor sludge confirmed the biodegradation of SA and 5-ASA. T he sequential anaerobic and aerobic bioreactor was able to completely remov e the sulfonated azo dye MY10 at a maximum loading rate of 210 mg MY10 (I-r eactor d)(-1) after the appropriate microorganisms for aerobic degradation of SA were bioaugmented into the aerobic bioreactor.