Transcript 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
• 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