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Heavy metals removal from mine runoff using compost bioreactors.
David Christian1, Edmund Wong, Ronald L Crawford
1Department of Biological & Agricultural Engineering, University of Idaho, Moscow, ID 83844, USA.
Environmental Technology
|February 1, 2011
Summary
Permeable bioreactors effectively treat mine runoff, removing most metals like Al, As, and Pb. Laboratory bioreactors showed superior metal reduction via sulfate-reducing bacteria compared to field-scale systems.
Area of Science:
- Environmental Engineering
- Geochemistry
- Microbiology
Background:
- Permeable bioreactors are increasingly recognized for mine wastewater treatment.
- Mine runoff poses environmental challenges due to metal contamination.
Purpose of the Study:
- To evaluate the performance of a field-scale permeable bioreactor (ML bioreactor) treating mine runoff.
- To compare the metal removal efficiency and mechanisms of the field-scale bioreactor with a laboratory-scale bioreactor.
- To investigate the role of bacterial sulfate reduction in metal precipitation.
Main Methods:
- A field-scale bioreactor with compost, straw, and gravel was operated at the Mother Load mine.
- A laboratory-scale bioreactor with a similar matrix treated similar mine runoff.
- Metals (Al, As, Cd, Fe, Ni, Pb, Zn, Mn) were assayed in both systems.
- Evidence of bacterial sulfate reduction and metal sulfide formation was examined.
Main Results:
- Both bioreactors efficiently removed Al, As, Cd, Fe, Ni, Pb, and Zn, but not Mn.
- Bacterial sulfate reduction and metal sulfide complex formation were observed in both systems.
- The laboratory bioreactor demonstrated higher proportions of immobile metal reduction than the ML bioreactor.
- Adsorption was identified as the primary metal removal mechanism in the ML bioreactor.
Conclusions:
- Permeable bioreactors are effective for removing various metals from mine runoff.
- Bacterial sulfate reduction plays a significant role in metal immobilization.
- Hydraulic residence time fluctuations in field-scale bioreactors can impact metal removal efficiency and mechanisms.
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