Constructed Wetlands http www hwr arizona eduglobesupportwetlands Kim
Constructed Wetlands http: //www. hwr. arizona. edu/globe/support/wetlands Kim Garcia, Donna King, Matt Kluvo, Kendrick Wilson and Desale Zerai
Introduction Dwindling Water Supplies l Water Shortages l Water Reuse l – “Natural” Technology – 30 Year Record in Global Water Treatment ~500 sub-surface systems in Europe ~600 surface flow systems in North America
Water Reuse l 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 of New Problems
Treatment Methods l Soil-Aquifer Treatment – The use of soil as a filter to reclaim wastewater l Phytoremediation – the use of plants to enhance the degradation of pollutants in wastewater.
Soil-Aquifer Treatment (SAT) l Relies on natural processes – Percolation – Adsorption l Affected By – – – Degree of Pre-treatment Depth to Groundwater and distance to recovery wells Operating schedules of percolation basins (Wet / Dry periods)
SAT Pre-Treatment l What is It? – WW treatment prior to wetland application • l 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) l Greatest Impacts of Pre-Treatment is on Total Oxygen Demand – Secondary Effluent >20 mg NH 3 -N/L TOD > 100 mg/L – Nitrified/Denitrified Effluent 0 mg NH 3 -N/L and 8 mg DOC/L TOD < 5 mg/L Aerobic conditions can be maintained with effluents that have low total oxygen demand.
Redox Conditions l 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) l Impacts – Disinfection By-Products – Anthropogenic Compounds • Trace organics l 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
Nitrogen l 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 (CO 2) for to promote degradation during infiltration
Phytoremediation The use of plants to degrade a variety of pollutants present in wastewater. Heavy Metals Trace metals Nutrients Organics Pathogens Diagram courtesy USEPA Office of Solid Waste http: //clu-in. org/download/citizens/citphyto. pdf
Phytoremediation Processes Phytoextraction or contaminant is concentrated in roots, stem Phytoconcentration and leaves Phytodegradation breakdown of the contaminant molecule by plant enzymes which act as to help catalyze Rhizosphere plant roots release nutrients to Biodegradation 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 Types Water Hyacinths Eichhornia crassipes Forage Kochia spp Poplar Trees Populus spp Willow Trees Salix spp Alfalfa Medicago sativa Cattail Typha latifolia Coontail Ceratophyllum demersvm L Bullrush Scirpus spp Reed Phragmites spp. American pondweed Potamogeton nodosus Common Arrowhead Sagittaria latifolia
Phytoremediation Effects l “A major effect of [wastewater] treatment with plants was elimination of the disturbing smell …” c l Water Hyacinth – Heavy Metals l Cattail, Reed – Nitrogen, TSS, BOD, COD l Degradation Releases
Sweetwater Wetlands
Sweetwater Wetlands l 2 ndary effluent l Filter Backwash from RRWWTP
Sweetwater Wetlands
Constructed Wetland Design Consideration – Sub. Surface 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 & 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 C 0
- E. g. One can roughly calculate the area needed for a domestic sewage using the ff equation (Vymazal et. al, 1998) A = Qd(ln. Co – ln. Ct) / KBOD where A = area Qd= ave flow (m 3/day) Co & Ct = influent & effluent BOD (mg/L) KBOD = 0. 10
Constructed wetland types - Typically a constructed wetland can be - surface flow ~ 0. 4 m - subsurface flow ~ 0. 6 m - horizontal - vertical
Mechanisms of waste removal - Facultative ponds - Floating aquatic plants - Rooted plants
Design features - Basic question - geographic - economic - Compartments - for resting - maintenance - unexpected events - Outlet considerations - Plant selection – Typha, Scirpus, Phragmites
Cold water wetlands - Increasing - Major problems - ice formation - and its effect on microbes and plants
Where? What, Wetland? l Surface Flow – – – l 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 Wetlands l Plants & Soil – Separate from Natural Environment – Can remove Soil and Plants during harvest time (iron lines) l Contaminated Water l Lots of Control l Expensive Compared to Surface Flow
Surface-Flow Treatment Wetlands l 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 l What happens to the plants after they absorb these pollutants? – Controlled burns – Decomposition – Harvested then burnt
How Aquatic Plants Remediate l Reduction-Oxidation in oxygenated Rhizosphere (toxic trace metals) l Accumulation of excess nutrients (N, P) into plant tissue l S, Fe, Cu, Se
Advantages to Creating l Education Outreach – Schools, k-12 + – Internships – Research l Recreation – Walking Trail – Birding l Wildlife Habitat – Migratory Birds – Opportunities for variety of wildlife
Habitat Creation l Though built to treat wastewater, constructed wetlands provide habitat for: – Birds – Mammals – Reptiles and Amphibians – Crustaceans – Fish
Wildlife l 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
Wildlife l 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 Wetlands http: //www. azstarnet. com/dailystar/snmedia/18572
Ethical Considerations l 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?
Wildlife l 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 habitat http: //www. mdc. mo. gov/landown/wetland/wetmng/18. htm
Wildlife l Invertebrates – Insects and crustaceans – Detritus feeders • Very important to treating the water • Help to break down nutrients and contaminants. Detritus feeder along the bottom. http: //www. mesa. edu. au/friends/seashores/deposit_feeders. html
Potential Risks Involved l 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 Control l 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 Sweetwater l Sweetwater Wetlands • Clearing away of overgrowth, I. e. brush and aquatic plants • Controlled burns • Larvacide • Use of adult pesticide when necessary
Mosquito Control Methods l Mosquito control in Sweetwater Wetlands http: //www. tucsonaudubon. org/birding/sweetwatermosquitoes. htm
Summary l Overall, mosquito problems can be dealt with using a combination of mosquito control solutions. l Benefits to wildlife, including endangered migratory bird species are important despite mosquito risk.
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