1. SOME RECENT ADVANCES IN PASSIVE TREATMENT OF MINED DRAINAGE Arthur W. Rose Pennsylvania State University

2. Topics  Advances in last 10 years since ADTI Handbook  Acidity  Oxic limestone drains  Upflow limestone beds, automated flushing  Sizing and flushing of vertical flow ponds  Sulfate-reducing bioreactors  Steel slag and chitin as reactants  Economic recovery of Fe sludge

3. ACIDITY  A key parameter for evaluating and sizing passive systems  Combines effects of pH, Fe, Mn, Al, alkalinity  Acidity by Standard Methods 1998 is a net acidity  Acidity can be calculated from pH,Fe,Mn,Al and alkalinity if suspended solids are low

4. Oxic Limestone Drains Useful for large flows of low-metal AMD (few mg/L) May be helped by periodic flushing Bed of limestone fragments Soil or cover Aerated AMD Cover retains CO2 and improves effluent alkalinity

5. Iron Removal  Net alkaline – aerate, degas CO 2  Net acid – use low-pH Fe oxidation by aerating and providing large surface area for microbes, then react with limestone

6. FLUSHING LIMESTONE BED Limestone Bed Flushing Control Capable of treating high-Al-Fe AMD Siphon or Smart-Drain-System Improved by occasional “washing” of limestone Can be designed in upflow mode

7. Flushing Limestone Bed Flushing control can be -Manual - <5% of Al is flushed -An automatic siphon started when pond is full -An Agridrain Smart Drain System using solar panel to operate a clock and open valve Flushing can remove 50% of accumulated precipitate See Hedin Environmental website

8. Smart Drainage System Flushing Siphon Timed Flusher

9. Vertical Flow Ponds (VFP’s, SAPS) water compost limestone Compost reduces ferric Fe and accomplishes sulfate-reduction Limestone neutralizes acidity Outflow goes to pond in which Fe oxidizes and precipitates Inflow

10. Sizing of VFP’s  Early VFP’s were designed with 12-24 hr. retention in limestone (ALD’s)  Some VFP’s release acid effluent despite long retention times  Field data shows a maximum acidity loading rate of 35 g/m 2 /day to generate alkaline effluent  Modeling shows this limit is explained by slow limestone reaction at pH greater than about 6, and CO 2 pressure  Design VFP’s with loading of 25-35 g/m 2 /d

11. Problems of VFP’s 1. Al >10-20 mg/L precipitates and coats limestone fragments  Manual flushing (monthly)  Automatic flushing (siphon or Smartdrain)  Add preceding flushed limestone pond 2. High influent Fe precipitates on top of compost and plugs flow  Capture in oxidation pond(s) before VFP, using low-pH iron oxidation  Add preceding flushed limestone pond

12. Problems of VFP’s (cont.) 3. Effluent is acidic despite long retention time  VFP is too small (use 35 g/m 2 /d)  Actual flow exceeds design flow (accurate flows and acidities needed for design) 4. Effluent is acidic, short retention time from testing  Short circuiting thru compost (along outside of cleanout pipes, thin compost, riprap thru compost, broken pipes).

13. Reliability of Large Passive Systems  Some consider passive treatment of more than minor flow and metals to be unreliable – Field evidence.  Most “failures” were not properly designed or constructed.  Some large systems do work.  Need concerted effort to evaluate “failures” and successes – Underway?  Use results to improve design.

14. SULFATE-REDUCING BIOREACTOR  Like VFP but only a single layer of compost mixed with fine limestone  Sulfate reduction is a major provider of alkalinity  Al precipitates as fine dispersed material that does not plug or coat limestone  Heavy metals removed as sulfide  Usually must be larger than VFP

15. SLAG BEDS  Some steel slag has high CaO, generates very alkaline water (1000 mg/L)  Run good water into slag bed and mix high alkalinity effluent with AMD  Use beds and dams of slag to neutralize AMD  Still experimental

16. CHITIN BEDS  Chitin (skeleton of crabs and other crustaceans) has finely interlayered CaCO3, chitin (organic matter) and N source. Lab and pilot tests show excellent neutralization and metal removal.  Still experimental

17. METAL RECOVERY  Hedin Environmental is selling selected Fe sludge, after processing, as pigment  Process is commercially profitable  Stream Restoration has recovered Mn oxides and sold small amounts for pigment, ceramics, etc.

18. Written Review  Available on ADTI website- wvwri.nrcce.wvu.edu/programs/adti /index.cfm  Paper in 2010 ASMR Proceedings

19. CONCLUSIONS o Many large passive systems have not performed to expectations, but reasons are becoming understood o Better design and construction, plus new technologies, allow passive treatment of a wider range of AMD