Published on January 7, 2008
Constructed Wetlands : Constructed Wetlands Kim Garcia, Donna King, Matt Kluvo, Kendrick Wilson and Desale Zerai http://www.hwr.arizona.edu/globe/support/wetlands Introduction: Introduction 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 Reuse: Water 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 of New 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-Treatment: SAT 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 Effluent 0 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 Conditions: Redox 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 Nitrogen: Nitrogen 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 Phytoremediation: 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: Phytoremediation Processes Various Plant Types: Various Plant Types Phytoremediation Effects: Phytoremediation Effects “A major effect of [wastewater] treatment with plants was elimination of the disturbing smell …” c Water Hyacinth – Heavy Metals Cattail, Reed – Nitrogen, TSS, BOD, COD Degradation Releases Sweetwater Wetlands: Sweetwater Wetlands Sweetwater Wetlands: Sweetwater Wetlands 2ndary effluent Filter Backwash from RRWWTP Sweetwater Wetlands: Sweetwater Wetlands Constructed Wetland Design: Constructed 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 & Hydrology: Wetland Design & Hydrology - Basic understanding of environmental factors, and their interactions is important for the design and construction of a wetland. Slide20: - The wetland needs to be designed according to - contaminant - absorption - sedimentation - chemical process, etc Slide21: - In addition design principles need to address - hydraulic load rate - residence time - plant density - inlet concentration C0 Slide23: - 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 types: Constructed wetland types - Typically a constructed wetland can be - surface flow ~ 0.4m - subsurface flow ~ 0.6m - horizontal - vertical Mechanisms of waste removal: Mechanisms of waste removal - Facultative ponds - Floating aquatic plants - Rooted plants Design features: Design features - Basic question - geographic - economic - Compartments - for resting - maintenance - unexpected events - Outlet considerations - Plant selection – Typha, Scirpus,Phragmites Cold water wetlands: Cold 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 Wetlands: Vertical-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 Wetlands: Surface-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 Creating: Advantages to Creating Education Outreach Schools, k-12 + Internships Research Recreation Walking Trail Birding Wildlife Habitat Migratory Birds Opportunities for variety of wildlife Habitat Creation: Habitat Creation Though built to treat wastewater, constructed wetlands provide habitat for: Birds Mammals Reptiles and Amphibians Crustaceans Fish Wildlife: Wildlife 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: Wildlife 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: Ethical 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? Wildlife: Wildlife 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: Wildlife 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: Potential 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 Control: Mosquito 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 Sweetwater: Mosquito 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 Methods: Mosquito 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.