REGENERATION OF DYE-SATURATED QUATERNIZED CELLULOSE BY BISULFITE-MEDIATED BOROHYDRIDE REDUCTION OF DYE AZO DROOPS - AN IMPROVED PROCESS FORDECOLORIZATION OF TEXTILE WASTEWATERS

Cellulosics modified to contain quaternary ammonium groups have a stro ng affinity for anionic dyes. Therefore, ion exchangers based on quate rnized cellulose or lignocellulose can be used to remove textile dyes from wastewater. However, restoration of exchanger binding capacity is poor using conventional, low-cost regenerants. Experiments were condu cted with two monoazo dyes, Orange II (Acid Orange 7) and Remazol Red F3B (Reactive Red 180), to determine whether reductive cleavage of dye azo bonds improves exchanger regenerability. Treatment with the redox couple KBH4/NaHSO3 fully restored the binding capacity of Orange It-s aturated quaternized cellulose. KBH4/NaHSO3 treatment of quaternized c ellulose saturated with Remazol Red F3B (hydrolyzed, unreactive form) restored 74% of the exchanger binding capacity, which increased to 95% with a subsequent wash with NaOH or NaClO4. High-performance liquid c hromatography was used to confirm that KBH4/NaHSO3 reductively cleaved dye azo bonds. Bisulfite was found to form a stable adduct with Orang e II but to not cleave the dye's azo bond. The efficiency of dye azo b ond reduction was the same for dye in solution and exchanger-bound dye . These results indicate that reduction of monoazo dyes is an efficien t method by which to regenerate the dye binding capacity of quaternize d cellulosics used to decolorize textile wastewater.