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Selenium Reduction in Constructed Wetland Treatment
Systems: Naturally Attenuating Problematic
Pollutants
Katie A. Bland, P.E. Burns & McDonnell
Senior Environmental Engineer
Overview
• What are Constructed Wetlands? • Why the Power Industry? • Westar Energy Pilot Project • Pilot Project Results • Full Scale Design/Construction • Path Forward
• Constructed Wetland Treatment System – “An artificial wetland created or restored…..for
anthropogenic discharge such as wastewater, stormwater runoff, or sewage treatment. Natural wetlands act as a biofilter, removing sediments and pollutants such as heavy metals from the water, and constructed wetlands can be designed to emulate these features.”
Constructed Wetland Treatment System
• Three General Systems – Free Water Cell – Vertical Flow Wetland – Vegetated Submerged Bed Wetland
Constructed Wetland Treatment System
• Free Water Surface Wetland
Constructed Wetland Treatment System
• Vertical Flow Bed Wetland
Constructed Wetland Treatment System
• Vegetated Submerged Bed Wetland
Constructed Wetland Treatment System
• Stormwater • Mine drainage • Domestic sewage • Landfill leachate • Fairly new to the power industry
CWTS in the Power Industry
A promising technology…
CWTS in the Power Industry
• Polishing FGD Wastewater
• Landfill leachate/CCR Contact Water
• Polishing Biological • Coal Pile Runoff • Stormwater
Westar Jeffrey Energy Center
Westar Jeffrey Energy Center
• Polishing FGD Wastewater – FGD Scrubber upgrade complete in 2008 – Low chlorides – Dewatering/solids removal already in place – Land available – Multiple options considered
• Multiple options considered, with some being complex mechanical systems with high capital costs
• Wide range in cost between CWTS and ZLD
Westar Jeffrey Energy Center
Constructed Wetland Project Jeffrey Energy Center
Plant Reuse
Makeup Lake
Pilot Wetland
Water / Material Balance
Constructed Wetland Project Jeffrey Energy Center
Pilot Wetland Construction Complete
Free Water Surface Cell
Vegetated Submerged Bed
Vertical Flow Bed Wetland Cell
Ecological Risks
Selenium and Mercury Ecological Exposure
Laboratory Column Studies
Pilot Constructed Wetland Results
CONSTITUENT MASS LOAD REDUCTION
AVERAGE INFLUENT
(ug/L)
AVERAGE EFFLUENT
(ug/L)
Mercury 83% 1.2 <0.2
Selenium 92% 114 12*
Boron 42% 3,459 2,120
Fluoride 93% 11,209 1,551
*Selenium: 31% non-detect ( < 5 ug/L )
Some Lessons Learned…
• Topsoil – Selenium • Economically viable • It works!
Full Scale Design/Construction
• Considerations for the full scale design – Further mitigate ecological risk – Flexibility of operation – Extensive Modeling
• Plant Water Balance • CORMIX
– Beneficial Reuse • Cooling tower feed
– Test Pad
Full Scale Design/Construction
• Design Incorporated Ecological Risk Assessment
• Very Long HRT in CWTS - 30+ Days • Synthetics & Upflow • Constructability Challenges
Isolate Mercury and
Selenium
Full Scale Design/Construction
Treatment Soil
Single Sided Geocomposite and Gravel Drains
Compacted Clay Liner (1x10-7 cm/sec)
Tier 1 Soil
Gravel/Sand Drainage Layer
Geotextile
60 MIL HDPE
Full Scale Design/Construction
Full Scale Design/Construction
Full Scale Design/Construction
• Earthwork completed in December of 2013 • Mechanical installation complete in May
2014 • Startup of system is ongoing
Full Scale Design/Construction
Full Scale Design/Construction
Wetlands = Opportunity
• CWTS effectively treats metals including Selenium and other constituents…
Potassium (K)
Aluminum (Al)
Fluoride (F)
Nitrogen (N)
Barium (Ba)
Boron (B)
Chromium (Cr)
Iron (Fe)
Molybdenum (Mo)
Selenium (Se)
Mercury (Hg)
Wetlands = Opportunity
• CWTS provide a green treatment solution that is appealing to the public and local stakeholders
• Edison Electric Award Winner 2014 • Economically appealing • Effective for metals reduction
