passive aeration using a trompe
DESCRIPTION
Tim Danehy and Bruce Leavitt, Consulting Hydro-geologist, BioMost, “Passive Aeration Using a Trompe“ Water aeration is needed at many mine drainage treatment facilities to oxidize ferrous iron or to remove dissolved carbon dioxide. Typical aeration accomplished through surface diffusion, cascade aeration, mechanical aeration, or with chemical reagents such as hydrogen peroxide. Using an ancient device known as a Trompe, it is possible to achieve the benefits of mechanical aeration without the need for electricity, motors, or any moving parts.TRANSCRIPT
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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
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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
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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.
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What is a TROMPE? continued
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Trompe History
• Discovered in 17th century Italy.
• Defining component of the Catalan Forge
• Developed 1 to 16 oz pressure
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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.
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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.
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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.
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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.
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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).
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Aeration Removes CO2 and Increases pH
H+ + HCO3- ↔ H2O + CO2 (g)
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Aeration Tests
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Aeration Tests
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Aeration Tests
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Aeration Tests
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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
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3 TROMPES in Series
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North Fork Montour Run
Aeration of Pond 2 at 125 gpm flow with 3 TROMPES in series
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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.
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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
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Semi-Active Lime DissolutionWater powered Lime Dosers.Long Dissolution Channel.Lime Buildup in Channel or Ponds.Carbon Dioxide Reacts to Form Calcite.
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Add Pebble Quicklime
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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.
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MixWell
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Lime Particles from MixWell
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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.
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A-Mixer
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Lime Particles from A-Mixer
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Pebble Quicklime
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Significant Cost Reduction
$30,000/yr.
$13,900/yr. est.
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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!)
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Questions