Constructed WetlandsConstructed Wetlands

Kim Garcia, Donna King, Matt Kluvo, Kendrick Wilson and Desale Zerai

http://www.hwr.arizona.edu/globe/support/wetlands

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

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

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.

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)

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

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.

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.

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

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

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

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

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

                                 

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

Sweetwater WetlandsSweetwater Wetlands

Sweetwater WetlandsSweetwater Wetlands

2ndary effluent Filter Backwash

from RRWWTP

Sweetwater WetlandsSweetwater Wetlands

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

Wetland Design & HydrologyWetland Design & Hydrology

- Basic understanding of environmental factors, and their interactions is important for the design and construction of a wetland.

- The wetland needs to be designed according to - contaminant - absorption - sedimentation - chemical process, etc

- In addition design principles need to address

- hydraulic load rate - residence time - plant density - inlet concentration C0

- 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

Constructed wetland typesConstructed wetland types

- Typically a constructed wetland can be

- surface flow ~ 0.4m - subsurface flow ~ 0.6m - horizontal - vertical

Mechanisms of waste removalMechanisms of waste removal

- Facultative ponds- Floating aquatic plants- Rooted plants

Design featuresDesign features

- Basic question - geographic - economic - Compartments - for resting - maintenance - unexpected events- Outlet considerations- Plant selection – Typha, Scirpus,Phragmites

Cold water wetlandsCold water wetlands

- Increasing - Major problems - ice formation - and its effect on microbes and plants

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

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

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)

Biomass Biomass

What happens to the plants after they absorb these pollutants?– Controlled burns– Decomposition – Harvested then burnt

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

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

Habitat CreationHabitat Creation

Though built to treat wastewater, constructed wetlands provide habitat for:– Birds– Mammals– Reptiles and Amphibians– Crustaceans– Fish

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

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

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?

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

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

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

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)

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

Mosquito Control MethodsMosquito Control Methods

Mosquito control in Sweetwater Wetlands

http://www.tucsonaudubon.org/birding/sweetwatermosquitoes.htm

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.