Decolorizing Textile Wastewater

When the textile industry dyes cotton fabrics, not all of the dye ends up on the fabrics. Some becomes a wastewater disposal problem. Decolorizing wastewater is expensive, but researchers hope to make the process cheaper and more environmentally friendly.

"An ideal dye adsorbent should allow the industry to reuse water rather than dump it—laden with dye and bleach—into streams after one use," says Joseph A. Laszlo. He is a chemist at the National Center for Agricultural Utilization Research in Peoria, Illinois.

Aware that a product called quaternized cellulose, although expensive, quickly binds ample amounts of acidic dyes to itself, Laszlo tried making a substitute from a crop residue instead of from purified cellulose.

Sugarcane bagasse, a cheap and plentiful by-product of sugarcane processing, seemed a good choice. And while bagasse is bulky and expensive to ship, it is produced in textile regions in Louisiana and Florida.

Laszlo converted finely ground bagasse into a quaternized anion-exchange resin. Quaternizing is a chemical process in which ammonium compounds introduce a permanent positive charge to a material. The same chemistry is applied in dyeing some cotton fabrics.

In his studies, Laszlo treated quaternized bagasse resin with epichlorohydrin to make it more durable and capable of adsorbing more dye. During adsorption, a thin layer of dye molecules adheres to the bagasse surface.

The research showed that quaternized bagasse resin adsorbed about 28 times as much of a textile dye—Remazol Brilliant Red F3B—as did untreated bagasse. And it was 16 times more effective than activated charcoal, a decolorizer commonly used in industrial wastewater treatments. The bagasse resin adsorbs the dye within 15 minutes, versus 2 hours for the activated charcoal.

Cost of chemicals for making each kilogram (2.2 pounds) of the bagasse resin was about $2.

Typically, a dollar's worth of resin would treat 1,325 gallons of wastewater containing more than a half pound of residual dye from treating 110 pounds of fabric. Moreover, the wastewater could be recycled.

Laszlo's studies show the biodegradable resin could also be recycled several times by treating it with sodium hydroxide. But with each recycling, the resin's ability to bind dye diminishes.

To further evaluate quaternized cellulose, Laszlo is scaling up the research and seeking industrial cooperators to speed technology transfer. — By Ben Hardin, ARS.

Joseph A. Laszlo is at the USDA-ARS New Crops and Processing Technology Research Unit, 1815 N. University St., Peoria, IL 61604; phone (309) 681-6322, fax (309) 681-6524.

"Decolorizing Textile Wastewater" was published in the July 1995 issue of Agricultural Research magazine.