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Optimizing Oxic Limestone Treatment of AMD using Automated Flushing Technologies

Optimizing Oxic Limestone Treatment of AMD using Automated Flushing Technologies Presented by Neil Wolfe, Hedin Environmental August 12, 2008 2008 Pennsylvania Abandoned Mine Reclamation and Coal Mining Heritage Conference.

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Optimizing Oxic Limestone Treatment of AMD using Automated Flushing Technologies

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  1. Optimizing Oxic Limestone Treatment of AMD using Automated Flushing Technologies Presented by Neil Wolfe, Hedin Environmental August 12, 2008 2008 Pennsylvania Abandoned Mine Reclamation and Coal Mining Heritage Conference

  2. Project funded through an innovative treatment grant from PA Department of Environmental Protection Bureau of Abandoned Mine Reclamation Grant administered by WPCAMR Technical components of project by Hedin Environmental

  3. Problem Statement

  4. Goals and Objectives • Quantify flushing effectiveness • Does it remove solids? • Does it prevent plugging? • Is it worth the cost? • Improve chemical performance • Produce compliant effluent • Improve efficiency • Reduce treatment cost • Limestone is the cheapest treatment chemical

  5. Evaluation of Existing Self-flushing Systems • Installed previously by Hedin Environmental • Jonathan Run (Beech Creek, Centre County) • Mitchell (Babb Creek, Tioga County)

  6. Jonathan Run Flushing Study Acidity - 280 mg/L Al - 45 mg/L Fe – 1 mg/L Mn – 8 mg/L Two parallel 30 CY roll off containers filled with ~33 tons limestone AASHTO #3 AASHTO #1 8” dosing siphons empty the containers in 3.6 minutes

  7. Mitchell Automated Flush System Acidity - 230 mg/L Al - 26 mg/L Fe – 9 mg/L Mn – 13 mg/L Mitchell Tank 50’ diameter concrete manure tank filled with 600 tons AASHTO #1 14” dosing siphon empties the tank in 15 minutes

  8. Construction of Experimental Flush Units Mitchell Site Two parallel 30 CY roll off containers filled with ~33 tons limestone Acidity - 230 mg/L Al - 26 mg/L Fe – 9 mg/L Mn – 13 mg/L Agri Drain SDS East Box West Box “Small” limestone

  9. Excavations of “fouled” limestone

  10. Cleaning of “fouled” limestone

  11. Findings thus far • Flushing maintains bed permeability • Flushing influences chemical performance • “Fouled” limestone can be cleaned • “Fouled” limestone can still treat water • Passive treatment of Al rich water is possible • Limestone based treatment is cheap

  12. Flushing maintains permeability

  13. Solids next to perforation

  14. Pore velocity doesn’t remove scale

  15. Flushing distributes solids

  16. Flushing removes only some of the solids *Preliminary

  17. Mitchell Tank Plumbing

  18. Flushing influences chemical performance Some flushing No flushing Fill and drain

  19. Interstitial goo

  20. Candy coated goodness

  21. “Fouled” limestone can be cleaned: The hose and excavator method

  22. “Fouled” limestone can be cleaned: Excavator only method

  23. “Fouled” limestone can be cleaned: Stone box method

  24. A temporary improvement • Cleaned limestone performance is less than that of new limestone, but close • Performance decline mirrors that of new limestone as well • Replenishment of limestone is important

  25. Chemical cleaning

  26. “Fouled” limestone can still treat water Performance spikes are due to cleaning events

  27. Passive treatment of Al rich water is possible • Typical good effluent: • pH 5.9 – 6.5; • alkalinity 10 – 40 mg/L CaCO3 (Net neutral to weakly net alkaline) • Dissolved metals < 2 mg/L • Particulate metals > 10 mg/L • Can get some Mn removal • High TSS requires settling • Never plug • Chemical failure before physical failure • Limestone becomes scaled

  28. Positive preliminary results from experimental system • West Box • Flow 2.5 gpm • Effluent pH 5.9 • Effluent Alkalinity 29 mg/L • 300 days of operation • Limestone was NOT cleaned • ~200 (g/m2)/day • ~0.2 ppd/ton

  29. Scheduled maintenance • Goal is to construct system that can still generate good effluent quality even after scale has formed on limestone • Maintenance (cleaning and replenishment) interval must be one year or more • A properly functioning system will dissolve limestone at a rate that makes replenishment necessary every few years.

  30. Oxic limestone treatment pros and cons • Pros • Compact footprint • Inexpensive • Cons • Little excess alkalinity • Limestone cleaning and replenishment requires long term funding commitment

  31. Limestone-based treatment is cheap What it costs – Based on experience thus far $0.12 per thousand gallons (O,M & R) $0.42 per thousand gallons (design & construct) $0.54 per thousand gallons (total cost) $587 per ton acidity removed (total cost) What you get Al and Fe removal, circum-neutral effluent For comparison Ziemkiewicz cites a cost of $291/ton acidity removed for in-stream lime dosing

  32. Questions?

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