Sludge Makes Sweet Tree Treat

Environment

A recent New Year's resolution to reduce the amount of process residuals going to its on‐site landfill has had excellent results for our Naheola, Alabama, consumer products mill and some sweetgum tree seedlings.

Facing the prospect of dwindling landfill space and a $30 million price tag to build a new one, Naheola's environmental team went looking for a place to put its process residuals.

"We started doing agricultural land application with our clarifier sludge and boiler ash and some lime mud and grits, but it's expensive, so we are looking for alternatives" says Shawn Williams, the mill's senior environmental engineer.

The mill then contacted large timber companies in the area to see if they would be interested in spreading the sludge and ash on their lands to promote tree growth.

"One of the companies asked if we had proof that it worked, so we established a partnership with Auburn University to find out," says Williams.

Putting it to the test

They set up 15 test plots on 10 acres of land using different mixtures of clarifier sludge and boiler ash, and in January 2016, planted their first "crop" of sweetgum seedlings. Sweetgums were chosen because they are native to the area and are faster‐growing hardwoods; the Naheola mill uses 60‐70 percent hardwood fiber in its operations.

The results have been impressive. After the first growing season, some of the 7‐inch seedlings had grown to 4 feet tall; in season two, some had reached a height of 7 feet. Virtually all the test plots that had the sludge/ash mixture were doing better than the control plot with no treatment.

"This is our first experiment with this soil mixture," says Steven Meadows, group manager – wood and fiber supply for the Naheola mill. "As we continue working with these materials, we could see even more beneficial effects."

Long‐term benefits

Williams is pleased that the success of the tests will provide another market for the mill's process residuals beyond applying them to agricultural lands. The application to timberlands isn't as frequent – it's spread after a tract of land has been cleared and then reapplied after the first tree thinning about a dozen years later. "But there's more timber acreage around here than we can ever cover with the amount of sludge and ash generated at the mill, so there's almost a continuous market for these residuals," Williams says.

And as for that New Year's resolution, by finding beneficial uses for process residuals, the mill has extended its landfill life by at least 20 years. In addition, says Williams, "Our pursuit of zero residuals to our landfill has good sustainability value. We can show our customers what we're doing, share our activities and results with other GP mills, and support the state of Alabama's recycling goal. It's a winner."