Recent literature reviewed in this paper indicates that although a large number of lab-scale studies have been conducted on decolourization of synthetic dye solutions through combined anaerobic-aerobic biodegradation, there is a need to generate relative performance data on industrial effluents. According to the concept of combined anaerobic-aerobic treatment, azo dyes should be removed from the water phase by (anaerobic) reduction followed by (aerobic) oxidation of the dyes' constituent aromatic amines. The anaerobic-aerobic reactor studies reviewed in this paper show that a generally high extent of color removal can be obtained, and several studies further more provide evidence for removal of aromatic amines. Combined anaerobic-aerobic treatment therefore holds promise as a method to completely remove azo dyes from wastewater. However, the results of the reactor studies reveal some possible limitations, both with respect to azo dye reduction and with respect to the fate of aromatic amines. Nevertheless, more research should also be conducted on the probable routes for the safe and eco-friendly way of handling the residues and byproducts obtained after decolourization process.

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