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Metal distribution and stability in constructed wetland sediment
Anna Sophia Knox1, Michael H Paller, Eric A Nelson
1Savannah River National Lab., Savannah River Site, 773-42A, Aiken, SC 20808, USA. anna.knox@srnl.doe.gov
Journal of Environmental Quality
|September 16, 2006
Summary
The A-01 wetland treatment system effectively removes copper and other metals from wastewater, with metals accumulating in the sediment layers over time. These metals are generally well-retained in the sediment, indicating successful long-term storage.
Area of Science:
- Environmental Engineering
- Ecotoxicology
- Water Treatment
Background:
- The A-01 wetland treatment system (WTS) utilizes giant bulrush for metal removal from National Pollution Discharge Elimination System (NPDES) effluent.
- Surface flow wetlands are employed for treating industrial wastewater containing heavy metals.
Purpose of the Study:
- To assess the effectiveness of the A-01 WTS in removing copper (Cu) and other metals.
- To investigate the accumulation, remobilization, and retention of metals within the wetland sediments over a five-year period.
Main Methods:
- Monitoring of metal concentrations (Cu, Zn, Pb) in water before and after treatment.
- Analysis of metal concentrations in different sediment layers (floc, organic, inorganic).
- Sequential extraction to determine potentially mobile fraction (PMF) and recalcitrant factor (RF) for metal remobilization and retention.
- Calculation of distribution coefficients (Kd) to evaluate metal exchangeability.
Main Results:
- The A-01 WTS achieved 60-80% reduction in Cu, Zn, and Pb concentrations in the effluent.
- Significant accumulation of Cu in wetland sediments, particularly in the floc and organic layers, over five years.
- High retention of Cu, Zn, and Pb was observed in organic and inorganic sediment layers (high RF), indicating strong binding.
- Manganese (Mn) showed lower retention in the floc layer.
- Distribution coefficients (Kd) were lower for Cu and Zn than for Pb, suggesting a more exchangeable fraction for Pb.
Conclusions:
- The A-01 WTS is effective in reducing metal concentrations in wastewater effluent.
- Wetland sediments act as a long-term sink for metals like Cu, Zn, and Pb, with strong retention mechanisms.
- Understanding metal binding and mobility in sediments is crucial for assessing the long-term efficacy and environmental impact of wetland treatment systems.
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