Passive Aeration Using a Trompe

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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.

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Passive Aeration Using a Trompe

  1. 1. Use of TROMPEs in Mine Drainage Treatment Bruce Leavitt1, Tim Danehy2, and Bryan Page2 1 Consulting Hydrogeologist 2776 S-Bridge Rd Washington, Pa. 15301 2 BioMost Inc. 434 Spring Street Ext. Mars, PA 16046
  2. 2. What is a TROMPE?  Water powered air compressor  Has no moving parts  Can be built from available plastic pipe  Does not require any electricity  Does not need much maintenance.  Produces about 1 cfm / 25 gpm
  3. 3. 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.
  4. 4. What is a TROMPE? continued
  5. 5. Trompe History • Discovered in 17th century Italy. • Defining component of the Catalan Forge • Developed 1 to 16 oz pressure
  6. 6. 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.
  7. 7. When is Aeration Needed?  When ferrous iron is present and  When the raw water has a low dissolved oxygen content.  When the raw water has elevated carbon dioxide.
  8. 8. Ferrous Iron Oxidation  Many mine drainage treatment facilities require aeration for iron oxidation.  Fe2+ + ¼ O2 + H+ → Fe3+ + ½ H2O  Based 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.
  9. 9. 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.
  10. 10. 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).
  11. 11. Aeration Removes CO2 and Increases pH H+ + HCO3 - ↔ H2O + CO2 (g)
  12. 12. Aeration Tests
  13. 13. Aeration Tests
  14. 14. Aeration Tests
  15. 15. Aeration Tests
  16. 16. TROMPE Design  TROMPES operate in a narrow flow range  Flow is dependent on pipe diameter  Four feet of head is required between inlet and outlet  Maximum pressure is dependent on the length of the return pipe  TROMPES can be constructed in parallel or series to meet flow and air requirements  TROMPES generate about 1 cfm / 25 gpm
  17. 17. 3 TROMPES in Series
  18. 18. North Fork Montour Run Aeration of Pond 2 at 125 gpm flow with 3 TROMPES in series
  19. 19. Oxygen Transfer  Oxygen 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.
  20. 20. 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
  21. 21. Semi-Active Lime Dissolution  Water powered Lime Dosers.  Long Dissolution Channel.  Lime Buildup in Channel or Ponds.  Carbon Dioxide Reacts to Form Calcite.
  22. 22. Add Pebble Quicklime
  23. 23. MixWell patent 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.
  24. 24. MixWell
  25. 25. Lime Particles from MixWell
  26. 26. A-Mixer patent 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.
  27. 27. A-Mixer
  28. 28. Lime Particles from A-Mixer
  29. 29. Pebble Quicklime
  30. 30. Significant Cost Reduction $30,000/yr. $13,900/yr. est.
  31. 31. Acknowledgments  Office of Surface Mining  PA DEP – Moshannon DMO  Montour Run Watershed Association  Allegheny Count Airport Authority  Gongaware Environmental Services  Kathy Leavitt (for allowing me to trompe around the back yard!)
  32. 32. Questions

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