UNCC Research Improves Sand Filter Effectiveness

Simplicity is the primary objective of the rapid sand filter system James Amburgey, Ph.D., is developing at the University of North Carolina, Charlotte.

“The idea is to make it as simple as possible,” Amburgey said. “All that is needed is some PVC pipe, sand, and inexpensive treatment chemicals. The only way to practically deploy a system to the people of less developed countries is for it to be inexpensive and simple.”

Amburgey specializes in drinking and recreational water treatment. He has done work in the past with slow sand filters, but his latest research with rapid sand filters is demonstrating the ability to clean water much more effectively and 30 to 50 times faster.

“One significant challenge with sand filters is in removing Cryptosporidium oocysts,” Amburgey said. “One ‘crypto’ is five microns in diameter, but the gaps between grains of sand are approximately 75 microns. So, we have to get the crypto to stick to the sand grains.”

To achieve this, Amburgey developed a chemical pretreatment scheme based on ferric chloride and a pH buffer that is added to the water. In its natural state, Cryptosporidium is negatively charged, as are sand grains, so they repel one another. The chemical pretreatment changes the Cryptosporidium surface charge to near neutral, which eliminates the natural electrostatic repulsion and causes it to be attracted to and stick to the sand grains via van der Waals forces.

In research using a prototype of this system in his lab, Amburgey and his students have done preliminary tests on waters from local rivers, creeks, and wastewater treatment plants. Their results are typically greater than 99 percent removal for Cryptosporidium-sized particles.

“A common problem in drinking water treatment facilities is that changing water quality requires changes in the chemical pretreatment dosages,” Amburgey said. “Our tests, so far, have shown that this system utilizing only a single set of chemical pretreatment dosages is effective on all waters tested to date.”

Another advantage of the system is that it can be adapted by using local sands or crushed rock that are indigenous to a particular region of the world.

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