Constructed Wetlands

1. Constructed Wetlands Kim Garcia, Donna King, Matt Kluvo, Kendrick Wilson and Desale Zerai http://www.hwr.arizona.edu/globe/support/wetlands

2. 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

3. 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

4. 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.

5. 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)

6. 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

7. 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.

8. 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.

9. 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

10. 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

11. 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

12. Phytoremediation Processes

13. Various Plant Types

14. 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

15. Sweetwater Wetlands

16. Sweetwater Wetlands • 2ndary effluent • Filter Backwash from RRWWTP

17. Sweetwater Wetlands

18. 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

19. Wetland Design & Hydrology - Basic understanding of environmental factors, and their interactions is important for the design and construction of a wetland.

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

21. - In addition design principles need to address - hydraulic load rate - residence time - plant density - inlet concentration C0

23. - 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

24. Constructed wetland types - Typically a constructed wetland can be - surface flow ~ 0.4m - subsurface flow ~ 0.6m - horizontal - vertical

28. Mechanisms of waste removal - Facultative ponds - Floating aquatic plants - Rooted plants

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

30. Cold water wetlands - Increasing - Major problems - ice formation - and its effect on microbes and plants

31. 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

32. 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

33. 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)

34. Biomass • What happens to the plants after they absorb these pollutants? • Controlled burns • Decomposition • Harvested then burnt

35. 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

36. Advantages to Creating • Education Outreach • Schools, k-12 + • Internships • Research • Recreation • Walking Trail • Birding • Wildlife Habitat • Migratory Birds • Opportunities for variety of wildlife

37. Habitat Creation • Though built to treat wastewater, constructed wetlands provide habitat for: • Birds • Mammals • Reptiles and Amphibians • Crustaceans • Fish

38. 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

39. 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

40. 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?

41. 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

42. 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

43. 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

44. 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)

45. 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

46. Mosquito Control Methods • Mosquito control in Sweetwater Wetlands http://www.tucsonaudubon.org/birding/sweetwatermosquitoes.htm

47. 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.