A 16th-century method may revolutionize mine drainage treatment
June 24, 2013 8:00 AM
Bruce Leavitt, designer and developer of trompe, explains the system, which has been installed in Findlay.
Bruce Leavitt, designer and developer of trompe, designed to treat mine drainage, shows a tour how the aeration system works.
By Don Hopey Pittsburgh Post-Gazette
A technology dating to the 16th century and built with PVC piping available at any Home Depot or Lowe's soon will be used to enhance and possibly revolutionize the treatment of abandoned mine drainage, still Pennsylvania's biggest water quality problem.
The technology, called "trompe," an old French word meaning trumpet, is a water-powered air compressor with no moving parts. It has been adapted and developed by Bruce Leavitt, a mining hydrogeologist, to provide enhanced aeration of polluted mine water, which speeds the cleanup process.
Use of trompe technology is especially applicable to the hundreds of mine discharges flowing out of the Pittsburgh coal seam in Western Pennsylvania, said Mr. Leavitt, during a walking tour of a trompe-enhanced passive treatment system on the North Fork of Montour Run in Findlay, 2 miles south of the Pittsburgh International Airport.
"Trompe can reduce the size and cost of passive treatment systems for mine drainage," he said, "And it can take a treatment system that's not working, or not working well, and clean the water better."
PG graphic: Passive aeration of mine water (Click image for larger version)
A trompe is a device that uses falling water to compress air. According to a paper submitted by Mr. Leavitt at a mine discharge symposium in March 2011 in Morgantown, W.Va., mine discharge can be collected into a trompe system where it is allowed to fall down a vertical pipe. The water falls faster than the air bubbles trying to escape up the pipe and so traps and compresses the air. At the bottom of the vertical pipe the water enters a horizontal separation chamber where water flows into a discharge pipe and the air escapes into vertical chambers and from there is piped up to the first mine discharge pool.
That compressed air is piped through submerged heads to aerate the mine discharge water in a bubbling pond, oxidizing the suspended iron and causing it to form heavier, rusty-orange particles that fall out of the water column and collect on the bottom of the pond.
Last week, approximately 65 gallons of water a minute was flowing through the three trompes installed on the North Fork treatment project, generating 5 cubic feet a minute of compressed air, Mr. Leavitt said. Those trompes, each with a four-foot vertical fall pipe, can handle almost twice that flow.
It's long been known that aeration speeds up the oxidation of iron and chemical reactions that occur during the treatment of mine water drainage, which pollutes more than 2,500 miles of streams and rivers in Pennsylvania. Through the years aeration has been accomplished by cascade aeration, mechanical aeration using electricity or expensive chemical treatments.
By using the ancient trompe technology it's now possible to get the benefits of mechanical aeration without the use of expensive motors, electricity or any moving parts, Mr. Leavitt said.
"Anyplace you would need aeration, whether an active or passive system, can use something like this," Mr. Leavitt said. "It's going to generate a lot of oxygen transfer."
In the 17th century, a trompe was used instead of a bellows by the Spanish to introduce compressed air into medieval Catalan forges for iron production. Use of trompe technology peaked in the late 19th century and early 20th century when it was used to provide compressed air to cotton mill forges and other industrial operations.
In 1910, the Ragged Chute trompe, the biggest ever built -- it had a 345-foot-long vertical fall -- began operation near Cobalt, Ontario, where it generated compressed air to run rock drills at a silver mine and, Mr. Leavitt said, "as a side benefit provide ventilation to the miners."
Tim Danehy, principal of BioMost Inc., a mining reclamation services company and project designer and consultant on the North Fork site, said the passive treatment system, involving a series of five ponds and a wetland, cost $674,000 in 2008, and was built to last 25 years. The cost of adding the three trompes to make the treatment system more efficient was about $30,000.
"You could go to Lowe's and buy all that stuff and that's part of the idea; to keep it all low-tech and low-cost. Of course the bigger the trompe the more it costs," he said.
In addition to the Findlay passive treatment site, trompe aeration units have been installed at the Curley site in Fayette County and the Manner site in Clearfield County, where it is used to drive an air lift mixer for mine drainage treatment.
Industry representatives on the North Fork tour were impressed. Jim Kelly, from Arch Coal, said the technology has potential if the mine drainage contains significant carbon dioxide, and Greg Mergenthaler, manager of environmental compliance at Carter Roag Coal Co. in Randolph, W.Va., said the demonstration project is producing "excellent results," noting, "That's water that will support aquatic life."
Lois Uranowski, chief of the Ecological Services and Technology Transfer Branch at OSM, said the development of the trompe technology grew out of the federal office's 2010 Applied Science Program.
"That year we asked the question, 'How do we improve water treatment?' And we received this proposal from Bruce Leavitt that is practical, simple and easily installed. We've had a lot of interest from Appalachian states and all over."