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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 • 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 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 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 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), Ohio State Wetland Research Center Treatment for Arizona CAFO (Feedlot) 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 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 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 Contami Site nant Process BOD5 Stems and Leaves Roots Bed media (gravel/sand) Microbial respiration Microbial respiration Microbial respiration Settling Nitrogen Leaves Algae in water column Roots Soil Bed media Volatilization (as N2 and N2O) NO3 and NH4+ -> Soluble Organic Nitrogen Ammonium -> Nitrate Nitrate -> N2, N20, or NH4+ Settling Phosphorus Stems and Leaves Roots\ Bed media (gravel/sand) Microbial Respiration Microbial Respiration Uptake Sedimentation/Burial Adsorption 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 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) Developing country model Wetlands in Arizona 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