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Treatment Wetlands – Constructed Wetlands. Chapter 20. History. German scientists used constructed basins with macrophytes to purify wastewater US researchers in the 1970s examined use of natural wetlands to treat wastewater EPA provides strong support for treatment wetlands. Approaches.

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Treatment Wetlands – Constructed Wetlands

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Treatment wetlands constructed wetlands l.jpg

Treatment Wetlands – Constructed Wetlands

Chapter 20


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History

  • German scientists used constructed basins with macrophytes to purify wastewater

  • US researchers in the 1970s examined use of natural wetlands to treat wastewater

  • EPA provides strong support for treatment wetlands


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Approaches

  • Natural wetlands – dump wastewater into existing wetlands “nature’s kidneys”

    • Before legal protection of wetlands

  • Constructed wetlands – built to mimic natural wetlands, not part of natural systems

    • Surface-flow – standing water most of the year

    • Subsurface-flow – water flows through porous substrate supporting one or two macrophytes


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Classification by Vegetation

  • 1. Free-floating macrophyte systems – water hyacinth, duckweed

  • 2. Emergent macrophyte – Phragmites, Typha

  • 3. Submerged macrophyte

  • 4. Forested

  • 5. Multispecies algal systems


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Early Studies

  • Max-Planck Institute, Germany – 1950s – created gravel bed macrophyte system, reduced bacteria, inorganic and organic chemicals, led to subsurface constructed wetlands across Europe

  • University of Florida – early 1970s – secondarily treated wastewater added to cypress domes at 2.5 cm/week. Lowered nutrients, heavy metals, microbes and viruses. Productivity increased.

  • University of Michigan – mid-1970s – dumped up to 5,000 m3/d of secondarily treated wastewater into a fen. Lowered ammonia N and total dissolved P, Cl didn’t change


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Wetland Types by Source

Municipal wastewater

Mine drainage – low pH, high iron, sulfate, aluminum, and trace metals

Stormwater and nonpoint source – seasonal, sporadic, variable flows.

Landfill leachate – collect and treat runoff from lined landfills, to reduce ammonium and COD

Agricultural wastewater – wastewater from concentrated animal feeding operations (CAFOs),


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Ohio State Wetland Research Center


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Treatment for Arizona CAFO (Feedlot)


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Wetland Design

– to integrate natural processes as much as possible

Hydrology – basis for biological and chemical conditions response

Hydroperiod and depth

Seasonal pulses

Hydraulic loading and detention rate

Optimum detention time from 5-14 days for municipal water


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Basin morphology

slopes of 6:1 to 10:1

Variety of depths allows multiple treatments

Deep – denitrification, increase sediment retention

Shallow - allows for more soil/water interaction and emergent vegetation

Series of cells can be used to enhance treatment


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Other Wetland Design Factors

  • Chemical loading

    • Important for nutrients and other chemicals – Fe, Selenium

  • Substrate/Soils

    • Organic matter important due to cation exchange capacity

    • Texture important in determining if it will be subsurface or overflow

  • Vegetation – few plants thrive in high nutrient conditions

    • Typha, Scipus, Phragmites, Lemna, Eichhornia crassipes


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Contaminant

Site

Process

BOD5

Stems and LeavesRootsBed media (gravel/sand)

Microbial respirationMicrobial respirationMicrobial respirationSettling

Nitrogen

LeavesAlgae in water columnRootsSoilBed media

Volatilization (as N2 and N2O)NO3 and NH4+ -> Soluble Organic NitrogenAmmonium -> NitrateNitrate -> N2, N20, or NH4+Settling

Phosphorus

Stems and LeavesRoots\Bed media (gravel/sand)

Microbial RespirationMicrobial RespirationUptakeSedimentation/BurialAdsorption


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Management

Plant removal – several times a year increases nutrient/chemical removal, stimulates growth

Mosquito control – use of mosquito fish (Gambusia affinis) and bacterial insecticides (Bacillus thuringensis (Bt), Bacillus sphaericus and Lagenidium giganteum)

Pathogen transmission – chlorination of municipal water, sampling


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Other benefits

Surface flow increases wildlife, may help in land building

Costs

Cost/ha decreases as size of wetland increases ($200,000/ha for 1-ha, $60,000/ha for 10-ha, $19,000/ha for 100-ha)

Generally cheaper than chemical treatments

Release much less CO2 than chemical treatment (Table 20-10)


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Developing country model


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Wetlands in Arizona


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Links

For treatment of manure waste

  • www.epa.gov/seahome/ manure/src/wetlands.htm

    Constructed wetland CADD drawings

  • www.sc.nrcs.usda.gov/ technical/constwet.html

    Images from Purdue

  • www.ces.purdue.edu/ onsite/alternatives.htm

    Wetlands for farm waste

  • msa.ars.usda.gov/.../ nsl/wqe_unit/wetlands.html

    For fecal sludge treatment in Thailand

  • www.sandec.ch/FaecalSludge/ pages/FSM-construc...

    In Arizona

  • http://ag.arizona.edu/OALS/ALN/aln45/wetlands.html#wetlands6anchor

    Remediation of mine tailings

    www.uc.edu/news/ wetlands.htm

    www.enviromine.com/ wetlands/Welcome.htm


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