Enhancing O 2 Transfer in Subsurface-flow Constructed Wetlands

1. Enhancing O2 Transfer in Subsurface-flow Constructed Wetlands T. P. Chan, N. R. Shah, T. J. Cooper, J. E. Alleman,R. S. Govindaraju School of Civil Engineering Purdue University May 16, 2005

2. Project Involvement INDOT: Financial support & technical guidance JTRP & Purdue: Research sponsorship ‘Hydraulic’ project: to track and evaluate flow rates and fate ‘Environmental’ project: to track wastewater treatment efficacy J.F. New: Sub-contracted design engineering for wetlands Indiana Department of Health: Wetland discharge permitting RQAW: Design engineering Heritage: Project construction

3. Basic Lagoon

4. Aerated Lagoon Floating Mechanical Aerator

5. Subsurface-Flow CW

6. Typical Wetland Plants

7. O2 Media Media Media O2 O2 O2 Plant Root O2 O2 Media Media O2 O2 Plant Root O2 O2 O2 O2 Plant Root O2 O2 Media O2 Media Media O2 O2 Media O2

8. Extensive bacterial Colonization of root tip surface area!

9. Media Media Media Plant Root • Constructed Wetland • Plants release oxygen via photosynthetic activity • High microbial activity on, and adjacent, to plant roots • However, oxygen may still be a critical limiting factor Media Media Plant Root Plant Root Media Media Media Media

10. Fill-and-Draw CW 'Draw' O2 Clean Water Waste

11. Fill-and-Draw CW 'Fill' Clean Water Waste

12. Fill-and-Draw CW 'Draw' O2 Clean Water Waste

13. Challenges at Rest Areas • Remote location • Rural locale • Away from existing sewer and POTW • High wastewater strength • Low-flush toilets • High variability in wastewater flow • Large increase in traffic volume during rush hours and holidays • Limited personnel

14. Project Location

15. Project Overview • Unique challenges • Long (3+ miles) sewer line to the city POTW • Low flush toilets; flow restrictive faucets • High strength wastes (BOD, Ammonia) • Odor problem at city lift station • Surcharges by the city • Pretreatment using constructed subsurface wetlands • Biofield (and city sewer) for effluent disposal

16. Greenfield Wetland System

17. Septic Tanks

18. Wetland Cells 1 & 2

19. Wetland Cells 1 & 2 Vegetated subsurface flow wetland Vertical filter

20. @ Outlet of Cells 1 & 2

21. Wetland Cell 3

22. Biofield

23. Automatic Sampler

24. Flow Meters

25. First Year in Operation • Wetland cells planted on August 12, 2003 • October 2003 – June 2004 • Startup period • Overflow mode • North side only • Mid June 2004 – present • Draw-and-fill mode (time-based) • Full Operation beginning in October

26. Daily Rainfall and Flow Totals Tailing response to rainfall - Daily Cycle - Weekly Cycle - Seasonal Cycle

27. D Outflow from Cells 1 & 2 No overflow Overflow at filling cell Draw-and-fill mode: 12-hour cycle during Saturday – Monday 24-hours cycle during Tuesday – Friday

28. Hydraulic Retention Time

29. Dynamic Modeling • Complex flow scheme • Changing water levels • Recirculation • Overflows • Simplifying assumptions • Treat wetland cells as giant buckets • Instantaneous overflow • Estimate HRT • Basis for design of similar systems

31. Hydraulic Retention Time *The value in parenthesis is the estimated HRT as if in the over-flow mode.

32. Wetland Performance • - Definite pattern of increased performance… • Obvious correlation with increased plant and root density • However, lagging ammonia removal problem!! • Strong suggestion that oxygen is limited! TSS % Removal BOD NH3 Days of Operation

33. Wetland Performance

34. Continuing/Future Activities • Continuing data collection and analysis • “Tweaking” the system for optimum treatment effectiveness • Additional of a surge tank • Development of hydraulic and treatment process model • Modifying existing wetland design guidelines, tailored to rest area application

35. The END … Visit our website: https://engineering.purdue.edu/ResearchGroups/Wetland

41. Wastewater Treatment Clean Water Waste ?

42. o o o Basic Lagoon Clean Water Waste • Very simple!

43. o Clean Water Waste o o Basic Lagoon O2 O2 O2 O2 O2 O2 O2 • Very simple! • However, mixing depends on wind! • Therefore, sometimes poorly mixed • Poor mixing means poor aeration • Oxygen supply will then be poor • Lagoon may stink!!

44. o Clean Water Waste o o Aerated Lagoon O2 O2 • Improved aeration • Better oxygen supply • Better biological kinetics • Smaller lagoon

45. Constructed Wetland (CW) Clean Water Waste

46. Characteristics Clean Water Waste • Constructed Wetland • Wetland plants tolerate routine submergence • High plant density • High plant root mass • High rate plant root release of oxygen • High bacterial growth on plant root surfaces • High biochemical degradation of waste

47. How Does it Work? Enhanced?Biometabolism Clean Water Waste

48. How to Increase DO? • Direct aeration • Rapid changes in water level • Expose thin water films and biofilms on the wetland substrate and plant roots to air • Large surface area  rapid and substantial oxygenation of the rhizosphere. • Greenfield rest area • Fill-and-Draw concept

49. Flow Data • Variability in flow • Daily Cycle • Weekly Cycle • Monthly Cycle • Extreme events: • High traffic volume during holidays • Rainfall • > 2-fold increase in daily flow • Effects of ET and rainfall • 1 mm ET / rainfall 300 gal decrease / increase in flow volume

50. Wetland Performance • Ponding • Lack of air-filled layer between water table and peat moss layer • Limited root growth • Invasive plant species • Overflows during the fill cycle • Short-circuiting