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 nant SiteProcess BOD 5 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 CO 2 than chemical treatment (Table 20-10)

Developing country model

Wetlands in Arizona

Links For treatment of manure waste manure/src/wetlands.htm Constructed wetland CADD drawings technical/constwet.html Images from Purdue onsite/alternatives.htm Wetlands for farm waste msa.ars.usda.gov/.../ nsl/wqe_unit/wetlands.html For fecal sludge treatment in Thailand pages/FSM-construc... In Arizona Remediation of mine tailings wetlands.htm wetlands/Welcome.htm