UF research: oyster shells hold promise as water cleanser

June 30, 2004

GAINESVILLE, Fla. — As living organisms, oysters help filter and clean seawater. Now, scientists may be able to broaden that natural cleansing ability by using the bivalves’ shells to rid fresh water of pollutants.

University of Florida and Korean researchers have developed and successfully tested a new process to convert waste oyster shells into a compound that cleanses water of phosphorus, a common pollutant in urban, agricultural and industrial runoff. The environmentally beneficial recycling technique appears to offer a way to use the millions of oyster shells produced annually as an unwanted byproduct of today’s mariculture operations – shells that until now have had few other uses.

“We see initial applications in Korea, but conceivably this could be applied anywhere in the world where you have intense mariculture,” said Ben Koopman, a UF environmental engineering professor and one of six authors of an article about the technique that appeared this spring in the journal Resources Conservation and Recycling.

Koopman said oyster shells contain large amounts of calcium carbonate, or limestone. In research beginning in 2000, a Korean research team headed by Chan-Won Lee, a professor of environmental engineering at Kyungnam National University in Korea, found that heating the shells at very high temperatures in a nitrogen-rich atmosphere for about an hour efficiently converts their contents into a form of calcium oxide. The compound is very similar to another compound, quick lime, used worldwide as a phosphorus remover and water softener, Koopman said.

Subsequent experiments in Korea and at UF revealed that the crushed-up oyster shell forces the phosphorus to leave the solution, become small particles and “precipitate out,” or fall to the bottom of the tank, where it can then be collected and discarded. The experiments also revealed the oyster compound could remove high concentrations of phosphorus from heavily polluted water “within a matter of minutes,” Koopman said. That might make it ideal for cleaning industrial wastewater, which typically has the highest concentrations of the mineral, he said.

And since the ingredients are free, a preliminary analysis suggests the process is competitive cost wise with traditional water-cleaning chemicals, he said. Recycling the oyster shells into the water treatment compound makes particular sense because intense mariculture often spurs coastal growth, he added. “You have more wastewater that has phosphorus in it that you need to remove,” he said.

Koopman can be reached at 352-392-7104 or by email at bkoop@ufl.edu.