Constructed Wetlands.ppt
Transcript of Constructed Wetlands.ppt
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Constructed WetlandsConstructed Wetlands
Kim Garcia, Donna King, Matt Kluvo, Kendrick Wilson and Desale Zerai
http://www.hwr.arizona.edu/globe/support/wetlands
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IntroductionIntroduction Dwindling Water
Supplies Water Shortages Water Reuse
– “Natural” Technology– 30 Year Record in
Global Water Treatment~500 sub-surface systems in Europe~600 surface flow systems in North America
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Water ReuseWater Reuse Reclamation of wastewater provides
– An alternative water source for Irrigation• Parks, Medians, schools and • Golf Courses
– Water Treatment• Secondary Wastewater • Backwash Water from WW Treatment Plant• Stormwater Runoff
– Riparian Habitat for Migratory birds
– Production ofNew Problems
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Treatment Methods Treatment Methods Soil-Aquifer Treatment
– The use of soil as a filter to reclaim wastewater Phytoremediation
– the use of plants to enhance the degradation of pollutants in wastewater.
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Soil-Aquifer Treatment (SAT)Soil-Aquifer Treatment (SAT)
Relies on natural processes
– Percolation– Adsorption
Affected By– Degree of Pre-treatment– Depth to Groundwater and distance to
recovery wells– Operating schedules of percolation basins
(Wet / Dry periods)
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SAT Pre-TreatmentSAT Pre-Treatment
What is It?– WW treatment prior to wetland application
• Filtration, chlorination, denitrification, biological treatment
Impacts WQ of Recharge Basin influent– Total Oxygen Demand– Biodegradable matter – Dissolved Organic
Carbon– Redox Conditions in saturated zone
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Total Oxygen Demand (TOD)Total Oxygen Demand (TOD) Greatest Impacts of Pre-Treatment is on Total
Oxygen Demand – Secondary Effluent
>20mg NH3-N/L TOD > 100mg/L
– Nitrified/Denitrified Effluent0 mg NH3-N/L and 8 mg DOC/L TOD < 5mg/L
Aerobic conditions can be maintained with effluents that have low total oxygen demand.
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Redox ConditionsRedox Conditions
Controlled by Pre-treatment– Through the regulation of the TOD of
the applied effluents– TOD influences redox conditions in the
saturated zone. • If dissolved oxygen is removed during percolation
through the vadose zone, anoxic conditions are likely to develop in the saturated zone…”
• Again, Aerobic conditions can be maintained with effluents that have low total oxygen demand.
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Dissolved Oxygen Content (DOC)Dissolved Oxygen Content (DOC)
Impacts – Disinfection By-Products– Anthropogenic Compounds
• Trace organics Removal
– Most DOC removed through top 10’ of soil – Long term monitoring has shown a slow
continuous reduction in DOC• Changes in specific UV Absorbance indicate
continuing microbial transformations
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NitrogenNitrogen Removal
– Pre-Treatment– SAT Alone
• Anoxic or anaerobic conditions necessary~> 50% removal
• Limited by – amount of biodegradable organic carbon• ANAMMOX – Ammonia Oxidation under anoxic conditions in
vadose zone converts ammonia to – Wetlands Treatment
• SAT + Phytoremediation • Much better removal • Plants provide an abundant carbon source (CO2) for to
promote degradation during infiltration
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PhytoremediationPhytoremediation
The use of plants to degrade a variety of pollutants present in wastewater.
Heavy MetalsTrace metals
NutrientsOrganics
PathogensDiagram courtesy USEPA Office of Solid Wastehttp://clu-in.org/download/citizens/citphyto.pdf
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Phytoremediation ProcessesPhytoremediation Processes
Phytoextraction or Phytoconcentration
contaminant is concentrated in roots, stem and leaves
Phytodegradation breakdown of the contaminant molecule by plant enzymes which act as to help catalyze
Rhizosphere Biodegradation
plant roots release nutrients to microorganisms which are active in biodegradation of the contaminant molecule
Volatilization transpiration of organics through leaves of the plant
Stabilization plant converts the contaminant into a form which is not bioavailable, or the plant prevents the spreading of a contaminant plume
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Various Plant TypesVarious Plant Types
Water Hyacinths Eichhornia crassipesForage Kochia Kochia spp
Poplar Trees Populus sppWillow Trees Salix spp
Alfalfa Medicago sativaCattail Typha latifolia
Coontail Ceratophyllum demersvm LBullrush Scirpus spp
Reed Phragmites spp. American pondweed Potamogeton nodosusCommon Arrowhead Sagittaria latifolia
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Phytoremediation EffectsPhytoremediation Effects
“A major effect of [wastewater] treatment with plants was elimination of the disturbing smell …”
cWater Hyacinth – Heavy MetalsCattail, Reed – Nitrogen, TSS,
BOD, CODDegradation
Releases
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Sweetwater WetlandsSweetwater Wetlands
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Sweetwater WetlandsSweetwater Wetlands
2ndary effluent Filter Backwash
from RRWWTP
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Sweetwater WetlandsSweetwater Wetlands
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Constructed Wetland DesignConstructed Wetland Design
Design Consideration – SubSurface Flow Systems
• Common in Europe– Surface Flow Systems
• More common in US/North America
• Marsh-like– Vertical Flow Systems
• New design used to overcome oxygen depletion problem and boost nitrification
Tucson Electric Park Detention Basin
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Wetland Design & HydrologyWetland Design & Hydrology
- Basic understanding of environmental factors, and their interactions is important for the design and construction of a wetland.
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- The wetland needs to be designed according to - contaminant - absorption - sedimentation - chemical process, etc
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- In addition design principles need to address
- hydraulic load rate - residence time - plant density - inlet concentration C0
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- E.g. One can roughly calculate the area needed for a domestic sewage using the ff equation (Vymazal et.al, 1998)
A = Qd(lnCo – lnCt) / KBOD
where A = area Qd= ave flow (m3/day) Co & Ct = influent & effluent BOD (mg/L) KBOD = 0.10
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Constructed wetland typesConstructed wetland types
- Typically a constructed wetland can be
- surface flow ~ 0.4m - subsurface flow ~ 0.6m - horizontal - vertical
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Mechanisms of waste removalMechanisms of waste removal
- Facultative ponds- Floating aquatic plants- Rooted plants
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Design featuresDesign features
- Basic question - geographic - economic - Compartments - for resting - maintenance - unexpected events- Outlet considerations- Plant selection – Typha, Scirpus,Phragmites
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Cold water wetlandsCold water wetlands
- Increasing - Major problems - ice formation - and its effect on microbes and plants
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Where? What, Wetland?Where? What, Wetland? Surface Flow
– best when large scale excess nutrient pollution problem– Farms+Fertilzer= algae blooms – Eutrophication =no oxygen fo fish– Mississippi Delta/Gulf of Mexico– Decomposition– Releases nutrients back into environment
Vertical flow– Safer and more effective at removing the more directly
harmful toxic trace metals– can chose specific plants– Can remove soil too
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Vertical-Flow Treatment WetlandsVertical-Flow Treatment Wetlands
Plants & Soil– Separate from Natural Environment – Can remove Soil and Plants during
harvest time (iron lines)Contaminated Water Lots of Control Expensive Compared to Surface Flow
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Surface-Flow Treatment WetlandsSurface-Flow Treatment Wetlands
Natural Flow Treatment Wetlands– Attempts to recreate a natural wetland– Water source is controlled. – More useful on large scale– Effective when excess nutrients– Trace metals remain in soil after harvest
(root to stem ratio)
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Biomass Biomass
What happens to the plants after they absorb these pollutants?– Controlled burns– Decomposition – Harvested then burnt
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How Aquatic Plants Remediate How Aquatic Plants Remediate
Reduction-Oxidation in oxygenated Rhizosphere (toxic trace metals)
Accumulation of excess nutrients (N,P) into plant tissue
S, Fe, Cu, Se
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Advantages to CreatingAdvantages to Creating Education Outreach
– Schools, k-12 + – Internships– Research
Recreation– Walking Trail– Birding
Wildlife Habitat– Migratory Birds– Opportunities for variety of
wildlife
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Habitat CreationHabitat Creation
Though built to treat wastewater, constructed wetlands provide habitat for:– Birds– Mammals– Reptiles and Amphibians– Crustaceans– Fish
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WildlifeWildlife
Birds– Variety of migratory and
non-migratory species– Major food sources include
submerged plants, plant seeds, grasses, fish, aquatic invertebrates, and terrestrial invertebrates that inhabit reeds and willows.
– Since many birds are migratory, the variety and number depends on the time of year.
Birders at the Sweetwater Wetlands locating waterfowl
http://www.azstarnet.com/dailystar/snmedia/18572
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WildlifeWildlife Birds (cont’d)
– Sweetwater Wetlands home to 125 species of birds
• Least Grebe (Tachybaptus dominicusand)
• Chestnut-sided warbler (Dendroica pensylvanica)
• Harris Hawk (Parabuteo unicinctus)
• Variety of duck species• Red-winged, yellow-headed,
and Brewer’s blackbirds• Song sparrows• Albert’s towhees• Shore and wading birds
Red-winged blackbird at Sweetwater Wetlandshttp://www.azstarnet.com/dailystar/snmedia/18572
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Ethical ConsiderationsEthical Considerations
Potential downside of birds in constructed wetlands– Contribute feces, which adds to the
nutrient-rich water being treated• Study at the Eastern Municipal Water District's Multipurpose
Demonstration Wetland near Hemet, California showed that bird feces did not cause significant problems for wastewater treatment.
– Is it ethical to encourage rare birds to inhabit contaminated water before it is completely treated?
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WildlifeWildlife
Mammals– Otter, water vole, water shrew, mink,
rats, etc.– In some constructed wetlands,
where previous conditions were not conducive to mammals, the distribution of wetland mammals is very limited.
– In the Sweetwater Wetlands, only mammals present are Arizona cotton rats (Sigmodon arizonae) and pack rats.
Muskrat in wetland habitathttp://www.mdc.mo.gov/landown/wetland/wetmng/
18.htm
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WildlifeWildlife
Invertebrates– Insects and crustaceans– Detritus feeders
• Very important to treating the water• Help to breakdown nutrientsand contaminants.
Detritus feeder along the bottom.http://www.mesa.edu.au/friends/seashores/deposit_feeders.html
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Potential Risks InvolvedPotential Risks Involved
Mosquitoes– Risk of West Nile virus, malaria, and other
mosquito-transmitted diseases– Constructed wetlands are by nature prime
mosquito habitat– Two types
• Stagnant water mosquitoes• Floodwater mosquitoes
– Constructed wetlands more conducive to stagnant water mosquitoes
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Mosquito ControlMosquito Control
Methods:– Steep concrete slopes– Deep bottoms– Introduction of larvivorous fish
• Mosquitofish (Gambusia affinis)– Very easily adaptable– Can cause other environmental problems by out
competing other fish species– Non mosquito-conducive plants– Mosquito-specific bacteria (Bacillus
thuringiensis and Bacillus sphaericus)
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Mosquito Control at SweetwaterMosquito Control at Sweetwater
Sweetwater Wetlands• Clearing away of overgrowth, I.e. brush and
aquatic plants• Controlled burns• Larvacide• Use of adult pesticide when necessary
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Mosquito Control MethodsMosquito Control Methods
Mosquito control in Sweetwater Wetlands
http://www.tucsonaudubon.org/birding/sweetwatermosquitoes.htm
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Summary Summary
Overall, mosquito problems can be dealt with using a combination of mosquito control solutions.
Benefits to wildlife, including endangered migratory bird species are important despite mosquito risk.