Researcher Finds Scrap Tires Useful For Filtering Wastewater

Every year, the United State produces millions of scrap tires, and finding adequate uses for these castoffs is a continuing challenge for researchers, regulators and communities.

Dr. Yuefeng Xie, associate professor of environmental engineering at Penn State-Harrisburg, has developed a method that uses crumb rubber to filter wastewater, according to a Nov. 17 announcement by the university.

"My research has found that crumb rubber derived from waste tires can be used as a filter media," Xie said. "The crumb rubber could be used for treating wastewater, ship ballast water and stormwater."

Crumb rubber is produced by chopping up and grinding up waste tires to a desired size, cleaning the rubber and removing any metal particles. It is currently being used in highway pavement, athletic track surfaces, playgrounds, landfill liners, compost bulking agents, various manufactured products, energy recovery and as artificial reefs for aquatic life.

For traditional wastewater filtration, gravity downflow granular filters using sand or anthracite as a medium are commonly used. One major problem with these filters is that upon backwashing the particles, the larger ones settle at a greater rate than the smaller ones. The Penn State researcher said that this causes the top of the filter bed to hold the smallest medium particles and the bottom to hold the largest, with the small medium particles or top layer of the filter tending to become clogged quickly.

In his research, Xie has found that crumb rubber is not a rigid material; instead it can be easily bent or compressed. Through the crumb rubber method, the larger solids are removed at the top layer of the filter, and the smaller solids are removed at a lower level, greatly minimizing the clogging problem.

Several studies conducted by Xie show that the crumb-rubber filter is much more cost effective than conventional sand or anthracite filters. Because of substantially higher water filtration rates and lighter weight in comparison to sand or anthracite, crumb-rubber filters also may be used in a mobile-treatment unit for disaster relief operations, he said.

Because the crumb rubber is compressible, the porosity of the particles is decreased, which resembles an ideal filter medium configuration, the researcher stated. It can then be used at higher filter rates while performing similarly to other media now in use. The crumb rubber media provide better effluent qualities, and larger media allow longer filter runs at higher flow rates.

Yuefeng Xie:

This article originally appeared in the 11/01/2006 issue of Environmental Protection.

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