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United States Department of Agriculture

Agricultural Research Service

Title: Regeneration of Dye-Saturated Quaternized Cellulose by Bisulfite-Mediated Borohydride Reduction of Dye Azo Groups -- An Improved Process for Decolorization of Textile Wastewaters

item Laszlo, Joseph

Submitted to: Journal of Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 10, 1997
Publication Date: N/A

Interpretive Summary: We showed previously that textile wastewater can be treated to remove colored contaminants (dyes) using chemically-modified cellulose or chemically-modified crop byproducts (which are composed of cellulose and similar materials). The wastewater dyes bind tightly to the modified cellulose, which can then be filtered and removed. However, because of the estrong association between dye and modified cellulose, reuse of the modified cellulose has not been feasible. The present work describes a simple chemical method by which the dye-binding ability of used, modified cellulose can be restored. A combination of strong reducing agents applied to the dye-cellulose complex breaks the dye into smaller molecules that are easily released from the cellulose. This procedure is inexpensive and uses chemicals already employed in textile dyeing. The findings of this work will allow textile companies to treat their wastewater at reduced expense by using the modified celluloses which can now be reused many times.

Technical Abstract: Cellulosics modified to contain quaternary ammonium groups have a strong affinity for anionic dyes. Therefore, ion exchangers based on quaternized 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 conducted with two azo 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 II-saturated quaternized cellulose. KBH4/NaHSO3 treatment of quaternized cellulose 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 chromatography was used to confirm that tKBH4/NaHSO3 reductively cleaved dye azo bonds. Bisulfite was found to for a stable adduct with Orange II, but no cleave the dye's azo bond. The consumption of reducing equivalents for azo bond reduction was the same for solution and exchanger phase dyes. These results indicate that reduction of azo dyes is an efficient method by which to regenerate the dye binding capacity of quaternized cellulosics used to decolorize textile wastewater.

Last Modified: 4/22/2015
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