Fate of azo dyes in sludges

The removal of color and organic matter contributed by the azo dye, 'Reactive Black 5,’ and Navy 106 wash water from a textile mill were studied in sludges under aerobic and anaerobic conditions. The potential of the dyes to leach from landfills was also investigated using Toxicity Characteristic Leaching Procedure (TCLP) analysis.

The vinyl sulfone group of the Reactive Black 5 dye appeared to enable the dye to sorb to biomass better than the hydrolyzed form of the dye. Sorption and aerobic color degradation of the hydrolyzed Reactive Black 5 dye and the Navy 106 wash water appeared to be related to biomass concentration. Little, if any, sorption or degradation of the dyes was observed with Blacksburg municipal treatment plant sludge which contained a biomass concentration of 3500 mg/L. However, sorption and degradation of wash water was observed with Peppers Ferry treatment plant sludge at a biomass level of 7000 mg/L. An inhibition to aerobic color removal of dye wash water was found at a higher color to biomass ratio. The inhibition to color degradation was accompanied by a lower rate of nitrate and sulfate release. TOC and COD of the dyes decreased under aerobic conditions. Under anaerobic conditions the color was degraded within a day. But the TOC and COD of the dye did not decrease. The TCLP extracts indicated the presence of little or no dye added to the reactors.