Constructed Wetlands

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Constructed Wetlands

  1. 1. Turning problems into assets:protecting coastal resources withconstructed wetlandsProf. Ron CarrollAssoc. DeanDirector-Science, River Basin CenterOdum School of EcologyUniversity of Georgia-Athens
  2. 2. Principal Collaborators• Laurie Fowler: international water law and policy, UGA• Prof. David Gattie: Environmental Engineering, UGA• Dr. Dianne Sanzone: Research Head, Energy andEnvironment, Batelle Labs• Prof. Manuel Spinola: Ecologist, National Univ. of CostaRica•Prof. William Tolner: Environmental Engineering, UGA
  3. 3. Problem StatementThe coastal zone is at the receiving endof excess nitrogen and phosphoruscausing fish kills and human health riskfrom…• blooms of toxic algae• dead zones due to depleted oxygen
  4. 4. The sources of these excess nutrients arestorm water run off, sewage and septicsystems, irrigation with fertilizers, all ofwhich also contaminate the coastal zonewith• pathogens• pesticides• other toxic chemicals
  5. 5. Due to highnitrogen andphosphorus…in wastewater fromsewage, septicsystems, livestock , andfertilizer run off withirrigation
  6. 6. “Dead zones” shown in red are a worldwide problem,especially along densely populated coastal zones
  7. 7. Coastal pollution from these non-pointsources will likely get worse in the U.S.because more than half the nation’spopulation lives in coastal counties and thesecounties generally experience the highestgrowth rates.
  8. 8. We need a better solution…..According to the American Society of CivilEngineers (2009) our wastewatertreatment systems should receive a gradeno better than D-.“Many systems have reached the end oftheir useful design lives. Older systems areplagued by chronic overflows during majorrainstorms ….and are bringing about thedischarge of raw sewage into U.S. surfacewaters.”
  9. 9. To be successful the “solution”must be…• broadly effective at meetingwater quality standards• affordable and cost-effectiveto build and manage• resilient to environmentalchange
  10. 10. To be successful the “solution”must be…• adaptable to new conditions• scalable to meet demandsfrom growing populations• accepted by the communityContinued
  11. 11. Constructed treatmentwetlands meet theseconditions
  12. 12. How they work: the surface flow designShallow zone Deep pools
  13. 13. Constructed wetlands with alternatingshallow aerobic and deep anaerobic cellsand sized properly….• reduce N and P below TMDL standards forswimmable streams• increase dissolved oxygen and greatlydecrease organic carbon• eliminate pathogenic bacteria and viruses
  14. 14. Constructed wetlands are often seen as acommunity assetFor example, the constructed wetlands of ClaytonCounty, Georgia are listed among the top five birdingspots in the mid-Atlantic
  15. 15. Attractive floweringplants can be used toincrease the aestheticsof the wetland
  16. 16. Overview of Panhandle Treatment Wetlandsin Jonesboro GA. Our principal research site.
  17. 17. Panhandle wetlands consist of twosequences of 8 treatment cells andone sequence of 6 cells. Each cell isabout 15m wide by 30m long anddivided into two deep pool areas,separated by a shallow area withdense cattails.The design allows a comparison oftreatment effectiveness along atransect.
  18. 18. Jenny Pahl at first treatment cell. Complete coverage byduckweed indicates high nitrogen levels…but nomosquitoes
  19. 19. Duckweed benefits• accumulates heavy metals• stores nitrogen (as protein)• fast growth (doubling time in days)• metabolites strongly inhibit mosquitolarval development
  20. 20. Note the very large number of baby duckweedwaiting for new space.
  21. 21. By cell 3 or 4 nitrate nitrogen, ammonia Nand phosphorus are at or below TMDLlimits for swimmable streams
  22. 22. N-fixing Azolla (red) in bottom pondindicates low levels of effluent nitrogen
  23. 23. Pathogenic, disease causing, bacteria and viruses areeliminated when the flow rate through the wetland isgreater than three days. Generally, flow rates are muchlonger in constructed wetlands.Pseudomonas auruginosa,a human respiratorypathogen sometimes foundIn wetlands.
  24. 24. Cañas wetland projectA developing country feasibilitystudy
  25. 25. Cañas, Costa Rica, Project TeamsUniversity of Georgia• Two ecology faculty plus students• Two environmental engineering faculty plus students• Two environmental design faculty plus studentsEARTH university, Costa Rica• Two environmental sciences faculty plus studentsNational University of Costa Rica• Two conservation ecologists plus students
  26. 26. Cañas, Costa Rica, is a small townrepresentative of other towns inthe seasonally dry Pacific side ofCentral America.Like all towns in this region, wastewater is poorly treated, if at all.
  27. 27. The Cañas River runsthrough the town andempties its polluted watersinto the head of the Gulf ofNicoya, a major domesticand export fisheriesresource.
  28. 28. We have initiated a feasibility study of lowcost options for cleaning and reusing Cañaswaste water while producing value-addedmarket assets.These assets include• Methane from anaerobic waste stabilizationponds• Biomass stock for renewable energy (ethanol ormethane) from constructed wetlands.
  29. 29. Waste stabilization (or oxidation) lagoons are the only sewage treatment facilities
  30. 30. Drainage ditch empties into the Cañas River
  31. 31. Circle encompasses area for constructed wetland. Cañas river is to the right.
  32. 32. Downstream tilapia farm.Nutrient rich effluent also contains male hormone ( syntheticandrogen).
  33. 33. The large amount of biomassproduced in constructed wetlandsis a source of renewable energy.Cattails and ethanol
  34. 34. Cattails play an important functional rolein contributing to restoration of waterquality by taking up N and P andproviding surface area for microbialdegradation of organic carbon anddestruction of pathogens.But, because their growth is so prolific,they must be periodically cut or burnedto maintain flow and prevent stagnantareas that would breed mosquitoes.
  35. 35. We propose harvesting cattails tomeet management objectives and,importantly, to produce significantrevenue.To accomplish this, the wetlandsmust be designed to allow harvestingwithout disrupting their function.
  36. 36. Parallel wetlands allow one to be drained andharvested while the other continues to function.
  37. 37. Our constructed wetland design for the Sewanee Utility District on theCumberland Plateau, Tennessee. Similar parallel wetlands would bedesigned for the Cañas project.
  38. 38. To get a sense of the revenue potentialfrom harvesting cattails and fermentingthem into ethanol, we can make acomparison to average ethanol yieldsfrom Iowa corn.
  39. 39. Ethanol from Iowa corn100 acres yields 32,364 gal.** Must add fertilizer, pesticides andfossil fuel
  40. 40. Ethanol from southeastern cattails inconstructed wetlands….100 acres yields approximately 102,287gal., three times the yield of Iowa corn.** Without fertilizer, pesticides or fossil fuel
  41. 41. At $2.40 per gallon (20ll market price), 100acres of constructed wetland cattails in thesoutheastern U.S.produces $245,487 gross revenue.
  42. 42. THE TAKE HOME MESSAGES…..WITH THE RIGHT DESIGN AND MANAGEMENT,CONSTRUCTED WETLANDS….• ARE BROADLY EFFECTIVE AT REMOVING EXCESSNUTRIENTS, AS MUCH AS HALF TON OF NITROGEN• AND DESTROYING PATHOGENS, PHARMACEUTICALS, ANDMANY TOXIC CHEMICALS• RESTORE OXYGEN AND REDUCE ORGANIC MATTER IN THETREATED WASTE WATER• DO NOT CREATE MOSQUITO PROBLEMS
  43. 43. • ARE SEEN AS AN AMMENITY BY THE COMMUNITY• ARE RELATIVELY AFFORDABLE AND EASY TO MANAGE• CAN PRODUCE SIGNIFICANT REVENUE FROMETHANOL AND SOMETIMES FROM METHANEConstructed wetlands (con’t)
  44. 44. THROUGH THEIR EFFECTIVEIMPROVEMENT OF WATER QUALITY,CONSTRUCTED WETLANDS CAN PROVIDESIGNIFICANT PROTECTION OF COASTALWATERS.THE STRONG ASSETS THAT ARE GENERATEDTHROUGH COMMUNITY SUPPORT ANDBIOMASS RENEWABLE ENERGY HELPENSURE THE LONG TERM VIABILITY OF THEWETLANDS AND THEIR PROTECTIVE ROLE.

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