An ISU professor has been researching different uses for lime sludge, the product left over after water has been treated for drinking.

Johannes van Leeuwen, professor of civil and construction engineering, has been working for the past year with Ames, Cedar Rapids and Des Moines on different methods of using the waste water treated for drinking.

When water is treated to make it soft, lime is added to the water, which settles out along with calcium and magnesium, said Phil Propes, superintendent of the Ames Water Treatment Plant. This mixture, called lime sludge, is sent to ponds to dry out and be taken away by contractors, he said.

Van Leeuwen said the question he posed for his research is, “How can we take the lime sludge and make it into a usable product?”

His research has resulted in several possible methods for getting rid of the lime leftovers.

One method is to substitute it for limestone, which van Leeuwen said has the same chemical properties, in the process of mixing cement.

“The four cement manufacturers use 1 million tons of limestone each year, and total production of lime sludge in Iowa is 100,000 tons per year, so it could easily be absorbed into cement production,” he said.

If lime sludge were used as a substitute for limestone, he added, the amount of mining would go down, which would save time and energy.

Another method being researched is a way to use the lime sludge to reduce emissions at coal-burning power plants. He said the lime sludge reacts with sulfur to remove sulfur dioxide from the air.

There are only two power plants in Iowa that would be able to use this system; the Muscatine power plant and the plant at Iowa State, van Leeuwen said.

“They are very keen and have been collaborating with us to find a way to use the lime sludge,” he said.

The Ames power plant wouldn’t benefit as it uses a low-sulfur coal, which doesn’t react with the lime, Van Leeuwen said.

Work has been conducted on the drying process of water treatment facilities, which takes a week, or even longer if it rains.

“A lot of the research is going to finding better drying methods,” van Leeuwen said.

Propes said the city of Ames produces 15 tons of lime sludge each day. That adds up to more than 5,000 tons per year.

Van Leeuwen said the demand from farmers, who use the leftovers to raise pH levels in the soil, isn’t great enough to use all of the sludge.

Eight percent of the total cost of water treatment goes to disposal of the sludge, and this cost is passed along to citizens through water bills, van Leeuwen said.

He said the Ames water facility alone spends $160,000 a year to get rid of the waste, Cedar Rapids spends $1 million per year, and that these numbers could potentially be lowered to save the city and residents money.

“If he can find other uses for the sludge, we gain because we get more ways to get rid of it,” Propes said.