Use of TROMPEs in Mine Drainage Treatment

Bruce Leavitt1, Tim Danehy2, and Bryan Page2

1 Consulting Hydrogeologist 2776 S-Bridge Rd Washington, Pa. 153012 BioMost Inc. 434 Spring Street Ext. Mars, PA 16046

What is a TROMPE?

Water powered air compressorHas no moving partsCan be built from available plastic pipeDoes not require any electricityDoes not need much maintenance. Produces about 1 cfm / 25 gpm

Principals of Operation

Falling water in a pipe entrains air.The high velocity water carries the air down the

pipe to an air separation chamber.Compressed air is separated from the water by

gravity.The air is collected for use.The water is discharged.

What is a TROMPE? continued

Trompe History

• Discovered in 17th century Italy.

• Defining component of the Catalan Forge

• Developed 1 to 16 oz pressure

Trompe History Continued

• Rediscovered by Charles Taylor, Canada

• Ragged Chutes Compressor delivered 128 psi to the area mines

• Was in continuous operation for over 70 years with only two maintenance shutdowns.

When is Aeration Needed?

When ferrous iron is present andWhen the raw water has a low dissolved

oxygen content.When the raw water has elevated carbon

dioxide.

Ferrous Iron Oxidation

Many mine drainage treatment facilities require aeration for iron oxidation.

Fe2+ + ¼ O2 + H+ → Fe3+ + ½ H2OBased on this equation 1 mg of DO will

oxidize 7 mg of ferrous iron.The time required for this reaction to occur

is dependent on oxygen transfer to the water and the pH of the water.

Effect of pH

After Dietz 2008

• The higher the pH the faster iron is oxidized.

• As iron is oxidized the pH is lowered lengthening the time required for oxidation.

• This increase in detention time requires a commensurate increase in pond size.

Effect of Carbon Dioxide

Mine drainage from underground mines frequently contains excess carbon dioxide.

The effect of this excess carbon dioxide is to lower the pH of the raw water.

Aeration of mine water will remove the excess carbon dioxide and could increase pH (Kirby et al., 2009).

Aeration Removes CO2 and Increases pH

H+ + HCO3- ↔ H2O + CO2 (g)

Aeration Tests

Aeration Tests

Aeration Tests

Aeration Tests

TROMPE Design

TROMPES operate in a narrow flow rangeFlow is dependent on pipe diameterFour feet of head is required between inlet

and outletMaximum pressure is dependent on the

length of the return pipeTROMPES can be constructed in parallel or

series to meet flow and air requirementsTROMPES generate about 1 cfm / 25 gpm

3 TROMPES in Series

North Fork Montour Run

Aeration of Pond 2 at 125 gpm flow with 3 TROMPES in series

Oxygen TransferOxygen transfer to water is dependent on:

– Air flow– Bubble size (fine bubbles have more surface

area)– Depth of aeration (10 feet is recommended)

Disc aeration heads used in sewage treatment produce fine bubbles.

Periodic cleaning is required.

Single TROMPE Cost

Gallons per Minute

Approximate Pipe Cost

Approximate Installation Cost Total Cost

20 to 100 $3,000 $9,400 $12,400

500 - 1000 $15,700 $16,800 $32,500

500 - 3000 $21,800 $24,268 $46,068

Semi-Active Lime DissolutionWater powered Lime Dosers.Long Dissolution Channel.Lime Buildup in Channel or Ponds.Carbon Dioxide Reacts to Form Calcite.

Add Pebble Quicklime

MixWellpatent pending

Raw water is feed to the bottom of the MixWell.

Lime or lime slurry is added to the annulus and sinks to the bottom.

The lime is agitated by the raw water.

Only small particles rise to the discharge.

MixWell

Lime Particles from MixWell

A-Mixerpatent pending

Compressed Air supplied by Trompe.

Airlift created in 12 inch pipe.

Circulation in tank keeps small particles suspended.

Airlift provides oxygen for iron oxidation.

A-Mixer

Lime Particles from A-Mixer

Pebble Quicklime

Significant Cost Reduction

$30,000/yr.

$13,900/yr. est.

Acknowledgments

Office of Surface MiningPA DEP – Moshannon DMOMontour Run Watershed AssociationAllegheny Count Airport AuthorityGongaware Environmental ServicesKathy Leavitt (for allowing me to trompe

around the back yard!)

Questions