title: Riboflavin as a redox mediator accelerating the reduction of the azo dye mordant yellow 10 by anaerobic granular sludge.
abstract: Azo dyes are important persistent pollutants of textile industry effluents. Reduction of these dyes to their corresponding aromatic amines under anaerobic conditions can be used to initiate biodegradation. Since electron transfer is suggested to be rate limiting, redox mediators are being considered to improve dye reduction kinetics. This study evaluates the use of riboflavin, the redox active moiety of common occurring enzyme cofactors, as a redox mediator to accelerate the reduction of the azo dye, mordant yellow 10 (MY10). Dye reduction was found to follow zero order kinetics, the total rate constant (Vtotal) could be separated into two components: the rate of reduction due to direct contact between enzymes in the sludge with the dye (Vdirect); and the rate of reduction mediated by riboflavin (Vmediated). Riboflavin increased the Vtotal by 61% at extremely sub-stoichiometric concentrations of 9.1 micromol l(-1), which corresponded to a molar riboflavin:dye ratio of 1:60. The accelerating effect of riboflavin displayed saturation kinetics at higher concentrations, with a maximum increase of Vtotal of approximately 2-fold. A model is presented which assumes that Vmediated depends on the activity of riboflavin reductase (RR) and thus follows Michaelis-Menton kinetics with respect to the riboflavin concentration. The half-velocity constant (Km) was very low (6.3 micromol l(-1)), indicating a high affinity of the sludge RR for riboflavin. Both Vdirect and Vmediated were found to be proportional to the assay sludge concentration. The results taken as a whole indicate that vitamin levels of riboflavin can be utilized to improve the kinetics of azo dye reduction during anaerobic treatment.
authors.affiliation: Department of Chemical and Environmental Engineering, University of Arizona, P.O. Box 210011, Tucson, Arizona, USA. Jimfield@email.arizona.edu
authors.forename: J A
authors.initials: JA
authors.lastname: Field
authors.forename: J
authors.initials: J
authors.lastname: Brady
mesh_terms: D001391:Azo Compounds / Q000378:metabolism*; D001421:Bacteria, Anaerobic / Q000502:physiology; D019149:Bioreactors; D004396:Coloring Agents / Q000378:metabolism*; D010084:Oxidation-Reduction; D017319:Photosensitizing Agents / Q000737:chemistry*; D012256:Riboflavin / Q000737:chemistry*; D013783:Textile Industry; D014865:Waste Disposal, Fluid / Q000379:methods*; D014873:Water Pollutants / Q000378:metabolism
chemical_list: D001391:Azo Compounds; D004396:Coloring Agents; D017319:Photosensitizing Agents; D014873:Water Pollutants; C483530:Mordant Yellow 10; D012256:Riboflavin