Biodegradability of reduced azo dyes : exploring the second stage of sequential anaerobic-aerobic treatment of azo-dye-containing wastewater

摘要

Sequential anaerobic-aerobic treatment is the most logical biological strategyfor the removal of azo dyes from wastewater. In the anaerobic stage, azo dyes,which generally resist aerobic biodegradation, are fortuitously reduced underanaerobic conditions, yielding colorless aromatic amines. In the aerobic stage,aromatic amines, which generally do not undergo further transformation underanaerobic conditions, are prone to oxidative (bio)transformation under aerobicconditions. Since research on aromatic amine biodegradation has beenusually conducted with relatively stable, not easily autoxidizing aromaticamines, representing only a part of the aromatic amines from azo dyes, stillmuch is unknown about the aerobic fate of azo dye cleavage products. In thisscreening study we investigated the biodegradability of seven chemicallyreduced azo dyes and two aromatic amines. The compounds were incubatedwith dyestuff-adapted sludge in the presence of either oxygen, perchlorate,nitrate, Fe(III) or Mn(IV) as the electron acceptors. CO2-production, O2-consumption and changes in HPLC-chromatograms and UV/VIS-spectra weremonitored. Preliminary results indicate that biodegradation had been limited torelatively simple benzene-based aromatic amines.