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Treatment Wetlands – Constructed Wetlands

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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  1. Treatment Wetlands – Constructed Wetlands Chapter 20

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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),

  7. Ohio State Wetland Research Center

  8. Treatment for Arizona CAFO (Feedlot)

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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)

  15. Developing country model

  16. Wetlands in Arizona

  17. 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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