Biodegradation of azo dyes in cocultures of anaerobic granular sludge withaerobic aromatic amine degrading enrichment cultures

A prerequisite for the mineralization (complete biodegradation) of many azo dyes is a combination of reductive and oxidative steps. In this study, the biodegradation of two azo dyes, 4-phenylazophenol (4-PAP) and Mordant Yell ow 10 (4-sulfophenylazo-salicylic acid; MY10), was evaluated in batch exper iments where anaerobic and aerobic conditions were integrated by exposing a naerobic granular sludge to oxygen. Under these conditions, the azo dyes we re reduced, resulting in a temporal accumulation of aromatic amines. 4-Amin ophenol (4-AP) and aniline were detected from the reduction of 4-PAP. 5-Ami nosalicylic acid (5-ASA) and sulfanilic acid (SA) were detected from the re duction of MY10. Subsequently, aniline was degraded further in the presence of oxygen by the facultative aerobic bacteria present in the anaerobic gra nular sludge. 5-ASA and SA were also degraded, if inocula from aerobic enri chment cultures were added to the batch experiments. Due to rapid autoxidat ion of 4-AP, no enrichment culture could be established for this compound. The results of this study indicate that aerobic enrichment cultures develop ed on aromatic amines combined with oxygen-tolerant anaerobic granular slud ge can potentially be used to completely biodegrade azo dyes under integrat ed anaerobic/aerobic conditions.