Azo dye biodegradation by microbial cultures immobilized in alginate beads.

Microbial degradation of azo dyes usually starts in anaerobic conditions with a reductive cleavage of the azo bond, followed by an aerobic step necessary for the degradation of the aromatic amines formed. Because some reductive processes take place also in presence of molecular oxygen, a one-step azo dye degrading process has been investigated. A microbial consortium able to degrade ethyl orange in aerobic conditions has been selected and immobilized in alginate beads coated with polyacrylamide resin. Different concentrations of ethyl orange have been completely degraded in the presence of 1% glucose or starch as cosubstrates, and different beads preparation procedures have been studied to determine the best condition for microbial degradation. The catalytic activity of the immobilized consortium improved during five serial processes carried out for 30 days at room temperature. Three pure cultures were then isolated from the consortium. The one with the greatest degrading activity, a filamentous fungus, had a degradative capacity similar to that of the whole consortium.