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Wetland Creation
• Why?• Can it be done?• Does a created
wetland serve the same ecological purposes as a natural wetland?
Why Build Treatment Wetlands?
• Improve water quality
• Secondarily, provide wildlife and other wetland functions.
Ecological Services
• biological filters• “nature’s kidneys”• “yada-yada-yada”-fact or more
environmental hype from tree huggers?
Not a new concept:– Germany in early 1950s– US in late 60s, dramatically increasing in
1970s
What’s the Goal?• Removal of contaminants from water
– contaminant-any undesirable constituent in the water that may directly or indirectly affect human or environmental health
– anything that degrades the water so that it cannot be used for its natural or intended purpose.
– might include:• toxic organics and metals• non-toxics-nutrients• thermal pollution
Uses
• Municipal wastewater
• Acid mine drainage (AMD)
• Landfill leachate
• Nonpoint urban/agriculture runoff
Municipal Wastewater Wetland
Acid Mine Drainage
Landfill Leachate Wetland
Agricultural Runoff Wetland
Types of Treatment Wetlands
1. natural wetlands-use for this often prohibited by laws created to protect them
2. surface flow wetlands
3. subsurface flow wetlands
What Can Be Treated?
• municipal wastewater (sewage)-residential and commercial sources; may range from single homes to regional scale– Iron Bridge wetland (FL) is 1200 A (480 ha)
• agricultural wastewater-runoff from cropland, pasture, milking and washing barns, and feedlots.
• industrial wastewater-pulp & paper manufacturing, food processing, slaughtering and rendering, chemical manufacturing, refining, and landfill leachate
Overview of Mechanisms of Contaminant Removal
Contaminant Removal Mechanisms
• Physical– especially good for sedimentation of particulates;
low velocity laminar flow– results in accumulation of solids– may be resuspended by wind-driven turbulence,
bioturbation (by humans or animals), and gas lifting (bubbling of methane, CO2, etc.)
• Biological• Chemical
Contaminant Removal Mechanisms
Biological-perhaps most important?– Plant uptake
• nutrients (NO3, PO4, ammonium)• toxics (bioremediation) e.g., lead, cadmium• rate of removal dependent on growth rate and
concentration of the contaminant in the tissue– woody plants sequester more and for longer times– herbaceous plants (e.g., Typha) have higher rates– Algae can be significant but are more susceptible to
toxicity of metals; however, have rapid turnover
• where does the contaminant go?– re-release; accumulation in peat
Contaminant Removal Mechanisms
Biological (continued)• Microbial processes
– may uptake contaminants in their biomass;– conversions by metabolic processes probably
more important• carbon -> CH4 or CO2; offgassing removes this C• inorganic Nitrogen (nitrate & ammonium)
– nitrate: denitrification facilitated by Pseudomonas spp.
NO3 -> N2; offgassing removes this N– ammonium: nitrification and denitrification facilitated by Nitrosomonas and Nitrobacter spp
NH4+ -> NO3 (aerobic) -> N2 (anaerobic)
Contaminant Removal Mechanisms• Chemical
– sorption (most important)• transfer of ions from solution phase (water) to solid
phase (soil)• includes adsorption and precipitation
– adsorption-attachment of ions to soil particles, either by cation exchange (weak attachment to negatively charged clay or organic particles); effective with ammonium and most trace metals (e.g., Cu2+)
» or chemisorption-stronger bonding attachment of some metals and organics to clays, iron or aluminum oxides, and organic matter; effective with phosphate
– precipitation-combine with iron and aluminium oxides forming new, stable, solid compounds; also production of highly insoluble metal sulfides, a way of immobilizing many toxic metals
Contaminant Removal Mechanisms• Chemical
– volatilization-diffusion from water to atmosphere
• e,g, ammonia (NH3) (aq) -> ammonia (gas)
iff pH > 8.5; if pH is less than that, N is in the form of ammonium which is not volatile
• many other organics are volatile
• increases air pollution?
Examples and Case Studies
Olentangy River Wetlands
at
The Ohio State University
It’s Good to be a
Buckeye!