Nitrogen Removal in Integrated Constructed Wetland Treating Domestic Wastewater
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Nitrogen Removal in Integrated Constructed Wetland Treating Domestic Wastewater

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Presentation at 2nd Irish International Conference on Constructed Wetlands for Wastewater Treatment & Environmental Pollution Control. 1-2 Oct. 2010

Presentation at 2nd Irish International Conference on Constructed Wetlands for Wastewater Treatment & Environmental Pollution Control. 1-2 Oct. 2010

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  • 1. 2nd Irish International Conference on Constructed Wetlands for Wastewater Treatment and Environmental Pollution Control 1st – 2nd October 2010 Nitrogen Removal in Integrated Constructed Wetland Treating Domestic Wastewater Mawuli Dzakpasu1, Oliver Hofmann2, Miklas Scholz2, Rory Harrington3, Siobhán Jordan1, Valerie McCarthy1 1 Centre for Freshwater Studies, Dundalk Institute of Technology, Dundalk, Co. Louth, Ireland. 2Institute for Infrastructure and Environment, School of Engineering, The University of Edinburgh, Edinburgh EH9 3JL. 3 Water Services and Policy Division, Department of Environment, Heritage and Local Government, Waterford, Ireland.
  • 2. Presentation outline • Introduction o Background o Aim and objectives • Case study description • Materials and methods • Results • Conclusions • Acknowledgements
  • 3. Background • Constructed wetlands used to remove wide range of pollutants • High removal efficiency (70% up) recorded for several pollutants e.g. COD, BOD5, TSS • Nitrogen removal efficiencies usually low and variable
  • 4. Background Integrated Constructed Wetlands (ICW) are: • Free water surface flow wetlands • Predominantly shallow densely emergent vegetated • Multi-celled with sequential through-flow
  • 5. Background Water treatment ICW Landscape fit concept Biodiversity enhancement ICW conceptual framework
  • 6. Background • Application of ICW as main unit for large-scale domestic wastewater treatment is novel • Limited information to quantify nitrogen removal processes in full scale industry-sized ICW
  • 7. Background Nitrogen biogeochemical cycle in wetlands
  • 8. Research aim and objectives Aim • To evaluate the nitrogen (N) removal performance of a full scale ICW Objectives • To compare annual and seasonal N removal efficiencies of the ICW • To estimate the areal N removal rates and determine areal first-order kinetic coefficients for N removal in the ICW • To assess the influence of water temperature on N removal performance of the ICW
  • 9. Case study description Location map of ICW site
  • 10. Case study description • Design capacity = 1750 pe. • Total area = 6.74 ha • Pond water surface = 3.25 ha • ICW commissioned Oct. 2007 • 1 pump station • 2 sludge ponds • 5 vegetated cells • Natural local soil liner • Mixed black and grey water • Flow-through by gravity • Effluent discharged into river
  • 11. Case study description Process overview of ICW
  • 12. Materials and methods Wetland water sampling regime • Automated composite samplers at each pond inlet • 24-hour flow-weighted composite water samples taken to determine mean daily chemical quality
  • 13. Materials and methods Water quality analysis • Water samples analysed for NH3-N and NO3-N using HACH Spectrophotometer DR/2010 49300-22 • NH3-N determined by HACH Method 8038 • NO3-N determined by HACH Method 8171 • Dissolved oxygen, temperature, pH, redox potential, measured with WTW portable multiparameter meter
  • 14. Materials and methods Wetland hydrology • − + + ( − − ) = • Onsite weather station measures elements of weather • Electromagnetic flow meters and allied data loggers installed at each cell inlet
  • 15. Data analysis and modelling − = × 100 (1) Co = influent concentrations (mg-N/L) Ce = effluent concentrations (mg-N/L) = × − (2) ℎ: = and = + − − q = hydraulic loading rate (m/yr.); Q = volumetric flow rate in wetland (m3/d); A = wetland area (m2); Qin = volumetric flow rate of influent wastewater (m3/d); P = precipitation rate (m/d); ET = evapotranspiration rate (m/d); I = infiltration rate (m/d)
  • 16. Data analysis and modelling − ∗ ∗ =− (3) − C* = background concentrations (mg/L); K = areal first-order removal rate constant (m/yr.) () = (20) (−20) (4) K(t) and K(20) = first-order removal rate constants (m/yr.); t = temperature (oC); = empirical temperature coefficient log = log − 20 + log 20 (5)
  • 17. Results 300 250 250 Rainfall (mm/month) 200 Discharge (m3/day) 200 150 150 100 100 50 50 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Influent Effluent Rainfall Average rainfall and wastewater discharge at ICW influent and effluent points (April, 2008 – May, 2010)
  • 18. Materials and methods 39 ± 27.9 m3 day-1 139 ± 65.7 m3 day-1 24.6 ± 12.7% 55.8 ± 11.3% 123 ± 61.8 m3 day-1 44.2 ± 11.3% 106 ± 112.2 m3 day-1 63 ± 371.3 m3 day-1 49.8 ± 23.3% 5.3 ± 2.7% 11 ± 9.4 m3 day-1 ICW water budget
  • 19. Results 100 Nitrogen (mg-N/L) 10 1 0 0% 1% 15% 29% 68% 96% 100% Influent Sludge Pond 1 Pond 2 Pond 3 Pond 4 Pond 5 pond Ammonia Nitrate Nitrogen removal with cumulative wetland area
  • 20. Results 100 Nitrogen (mg-N/L) * 10 * * * * * * 1 Summer Autumn Winter Spring Summer Autumn Winter 2008 2009 Ammonia Nitrate Seasonal variations of influent nitrogen to ICW * Indicates significant seasonal variation (P < 0.01, n = 18)
  • 21. Results 10 Nitrogen (mg-N/L) * * 1 * * * * * 0 Summer Autumn Winter Spring Summer Autumn Winter 2008 2009 Ammonia Nitrate Seasonal variations of effluent nitrogen from ICW * Indicates significant seasonal variation (P < 0.01, n = 18)
  • 22. Results 100 12 Removal Effiiency (%) 80 10 HLR (mm/d) 8 60 6 40 4 20 2 0 0 Summer Autumn Winter Spring Summer Autumn Winter 2008 2009 Ammonia Nitrate HLR Seasonal variations of nitrogen removal efficiency and hydraulic loading rate
  • 23. Results 1800 Removal Rate (mg m-2 d-1) y = 0.988x - 1.551 1200 R² = 0.99 600 a) Ammonia 0 0 600 1200 1800 Loading Rate (mg m-2 d-1) Removal Rate 1000 (mg m-2 d-1) 750 y = 0.952x - 0.111 R² = 0.99 500 250 b) Nitrate 0 0 250 500 750 1000 Loading Rate (mg m-2 d-1) Areal nitrogen loading and removal rates
  • 24. Results Areal first-order nitrogen removal rate constants in ICW K (m/yr) K20 (m/yr) Parameter  Mean SD n Mean SD n Ammonia 14 16.5 120 15 17.3 101 1.005 Nitrate 11 12.5 101 10 11.3 101 0.984 n = sample number, SD = standard deviation
  • 25. Results 120 y = -0.081x + 15.56 KA (m/yr) R² = 0.0004 60 (a) Ammonia 0 0 5 10 15 20 25 Water temperature (oC) 80 y = -0.098x + 11.98 KN (m/yr) R² = 0.0009 40 (b) Nitrate 0 0 5 10 15 20 25 Water temperature (oC) Water temperature and reaction rate constants
  • 26. Results 120 y = 0.05x + 2.23 KA (m/yr) R² = 0.77 60 (a) Ammonia 0 0 500 1000 1500 2000 Loading rate (mg m-2 d-1) 100 y = 0.09x + 4.23 KN (m/yr) R² = 0.66 50 (b) Nitrate 0 0 200 400 600 800 1000 Loading rate (mg m-2 d-1) Nitrogen loading rate and reaction rate constants
  • 27. Conclusions • High removal rates recorded at all times of the year • Removal efficiency consistently > 90 % • Removal rates slightly influenced by seasonality • Strong linear correlations between areal loading and removal rates: NH3-N (R2 = 0.99, P < 0.01, n = 120) and NO3-N (R2 = 0.99, P < 0.01, n = 101) • Low temperature coefficients are indications that variability in N removal was independent of water temperature
  • 28. Acknowledgements • Monaghan County Council, Ireland for funding the research. • Dan Doody, Mark Johnston and Eugene Farmer at Monaghan County Council, Ireland, and Susan Cook at Waterford County Council, Ireland, for technical support.
  • 29. Thank you for your attention! We welcome your questions, suggestions, comments! Contact: mawuli.dzakpasu@dkit.ie