Biodegradation of azo dyes by bacteria inoculated on solid media

Bacteria were inoculated on different solid media to attain biodegradability of an azo dye (Acid Orange 7). Kaolin, bentonite and powdered activated carbon (PAC) were selected to be used with cultures of Enterobacter, Pseudomonas and Morganella sp., as bacteria would be able to degrade several textile dyes. For the solid, to be employed as media, special characteristics are needed with regards to adsorption capacity for concentrating substrate within the cell environment and an adequate particle size and surface texture for assuring bacterial colonization. Only PAC with 0.490 mm particle size shows these characteristics among the solids used and it was colonized by a high number of cells from the three cultures. Dye was degraded following a second-order kinetics. A mechanism for dye degradation is proposed in which anaerobic and aerobic microniches in the PAC particle perform cleavage of the azo bond and oxidation of the amines formed in the same biocatalytic particle.