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NEWS
Method Developed That Removes Color From Water
September 14, 2018

Dyes are widely used in industries such as textiles, cosmetics, food processing, papermaking and plastics. Globally, we produce about 700,000 metric tons — the weight of two Empire State Buildings — of dye each year to color our clothing, eye shadow, toys and vending machine candy.

During manufacturing, about a tenth of all dye products are discharged into the waste stream. Most of these dyes escape conventional wastewater-treatment processes and remain in the environment, often reaching lakes, rivers and holding ponds, and contaminating the water for the aquatic plants and animals that live there. Even just a little added color can block sunlight and prevent plant photosynthesis, which disrupts the entire aquatic ecosystem.


University of Washington researchers created a sponge-like material, left, from wood pulp and small bits of metal that can remove color from dyes in water within seconds. More of the material is shown in the tubes on the right. Credit: Mark Stone/University of Washington.

A team led by the University of Washington (UW) has created an environmentally friendly way to remove color from dyes in water in a matter of seconds. The technique was described in a paper published online recently in the journal Applied Catalysis B: Environmental.

“A small amount of dye can pollute a large volume of water, so we needed to find a way to very quickly and efficiently remove the color,” said senior author Anthony Dichiara, an assistant professor of bioresource science and engineering in the UW School of Environmental and Forest Sciences. “We were pretty impressed with what we were able to achieve.”

According to information, the research team developed a method that removes color from water using a sponge-like material they created from wood pulp and small bits of metal. Cellulose, the main structure in plant cell walls and the most abundant natural material on Earth, provides the backbone of the material, which is decorated with tiny pieces of palladium. This metal serves as a catalyst to help remove color quickly.

Instead of removing dye from water, the research team sought to change the color of the dyes to something that falls outside of what we can see in the visible spectrum. A chemical reaction can, for example, disrupt the color red and make it appear clear, or colorless. In the case of dye waste products that artificially color the water in lakes and prevent photosynthesis, changing the dye from red to clear should allow plants to grow normally again.

The chemical reduction of dyes using molecules called “reducing agents” can alter the dye structure and change its color from red or blue to clear. However, the reaction is not very efficient and can take weeks to occur. The UW’s material contains a catalyst that works with the reducing agent to speed this process up to almost instantaneous.

In the new paper, the researchers describe the simple and sustainable process they developed to make the color-removing material. The researchers combined cellulose molecules with palladium metal, heated the solution and mixed it in a blender. Then they purified and freeze-dried the material so it became a porous, reusable substance. The resulting sponge is more than 99 percent air — its large pores allow water to flow in and out, while the metal catalyst particles within the material work to remove any color present.

Funding for this work is from the Guangdong Provincial Department of Science and Technology, the U.S. Department of Agriculture’s National Institute of Food and Agriculture, and the Bureau of Guangdong Forestry.


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