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Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

Mawuli Dzakpasu
Mawuli Dzakpasu

The document summarizes a study assessing nutrient leaching and groundwater quality near an integrated constructed wetland treating domestic wastewater. Key findings include: 1) The constructed wetland was very effective at removing nutrients like ammonia, nitrates, and phosphates from wastewater, achieving over 80% removal on average. 2) Leachate from the wetland cells contained high levels of ammonia but generally low levels of nitrates and phosphates. 3) Low infiltration rates from the wetland may not immediately threaten groundwater quality. 4) Groundwater nutrient levels were generally low except near sites with peat in the soil, which saw slightly elevated ammonia levels.

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Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater Society of Wetland Scientists, European Chapter, Annual Meeting 26th May 28th May 2010 Mawuli Dzakpasu1, Oliver Hofmann2, Miklas Scholz2, Rory Harrington3, Siobh叩n Jordan1, Valerie McCarthy1 1 National Centre for Freshwater Studies, Dundalk Institute of Technology, Dundalk, Co. Louth, Ireland. 2Institute for Infrastructure and Environment, School of Engineering, University of Edinburgh, Edinburgh EH9 3JL, UK. 3 Water Services and Policy Division, Department of Environment, Heritage and Local Government, Waterford, Ireland.
Presentation Outline Introduction Objectives Materials and methods Results and discussions Conclusions Acknowledgements
Introduction Domestic wastewater may contain high levels of nutrients (N & P). Nutrients are significant pollutant sources. National and EU legislation require enhanced management of pollutant sources. Constructed wetlands have been used with rather positive but variable results.
Introduction Integrated Constructed Wetlands (ICW) are: Free water surface wetlands. Predominantly shallow emergent vegetated. Multi-celled with sequential through-flow.
Introduction The ICW concept explicitly integrates three basic objectives: 1. Sustained capacity to contain and treat water. 2. Landscape fit that enhances site aesthetic and economic values. 3. Enhancing biodiversity and habitats. ICW concept therefore addresses priority areas of the WFD.
Introduction Key questions for ICW: Are ICW systems a potential threat to receiving waters? Are local soil materials capable of providing effective protection to underlying and associated groundwater?
Research Objectives To evaluate nutrient removal rate in ICW treating domestic wastewater. To estimate rate of infiltration and nutrients leaching through the ICW cell beds. To assess groundwater nutrient concentration near the ICW.
Case Study Description Design capacity = 1750 pe. Total area = 6.74 ha Pond water surface = 3.25 ha ICW commissioned Nov. 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
Macrophyte Composition at ICW Phragmites australis Carex riparia Typha latifolia Iris pseudacorus Glyceria maxima
Overview of ICW Sections Overview of Sludge Pond Overview of Pond 1 Overview of Pond 3 Overview of ICW Outfall Overview of Pond 5
Materials and Methods Water Quality Monitoring 1. Wetland water sampling Automated composite samplers at each pond inlet. 24-hour flow-weighted composite samples are taken to determine the mean daily chemical water quality. Grab samples taken for other physical water quality.
Materials and Methods 2. Groundwater sampling Eight piezometers placed within ICW. Piezometers placed along suspected flow paths of contaminants. Piezometers are 3-5 m deep. Depth to water ~2 m Samples taken weekly. Water level measured before purging piezometers.
Materials and Methods BH1 BH2 BH4 BH3 Sub-soil Geology BH8 Till dominant Alluvium BH7 Peat (mainly near BH3, BH7) BH5 Coefficient of permeability of 9.07x10-11 m/s BH6 Location of piezometers
Materials and Methods 3. Leaching water monitoring Gravity pan lysimeters placed below first three ponds. 920 mm diameter. 0.7 m below pond beds. Provide sample of infiltrating water (quantity & quality). Samples collected over 24 hours by attaching bottle to outlet pipe.
Materials and Methods L3 L2 L1 L5 L4 L8 L6 L7 Location of lysimeters
Materials and Methods Water Quality Analysis Nitrogen: TN, ammonia, nitrate. Phosphorus: TP, MRP. Organic matter: BOD5 ,COD, SS. dissolved oxygen, pH, temperature, redox potential, electrical conductivity, total and faecal coliforms. Analysis done weekly according to Standard methods (APHA, 1998).
Results and Discussions Table 1: Influent Composition of ICW ICW Influent Standard Number of Parameter (mean concentrations) Deviation samples COD (mg O2/L) 1178 642.1 101 BOD5 (mg O2/L) 853 552.5 99 Ammonia (mg/L NH4+) 34 10.5 108 Nitrate (mg/L NO3-) 6 5.7 98 Molybdate Reactive 3-) 4 2.3 102 Phosphate (mg/L PO4
Results and Discussions Table 2: Effluent Composition from ICW ICW Discharge Standard Number Parameter (mean concentrations) Deviation of samples COD (mg O2/L) 37 26.7 104 BOD5 (mg O2/L) 4.9 5.1 99 TSS (mg/L) 8.9 18.0 100 Ammonia (mg/L NH4+) 0.8 1.7 108 Nitrate (mg/L NO3-) 0.3 0.3 101 Molybdate Reactive 0.03 0.04 100 Phosphate (mg/L PO43-) E. Coli (CFU/100mls) 2 2 5
Results and Discussions 120 Removal Efficiency (%) 100 80 60 40 20 0 Ammonia Nitrate Phosphate MRP 2008 2009 Fig. 1: Average annual treatment efficiency of ICW
Results and Discussions 200 Removal Rate y = 1.0014x - 0.997 150 (g/m2/year) R族 = 0.9954 100 (A) 50 0 0 50 100 150 200 Loading Rate (g/m2/year) (C) 50 Removal Rate 40 y = 0.9845x - 0.3062 (g/m2/year) R族 = 0.9954 30 20 (B) 10 0 0 10 20 30 40 50 Loading Rate (g/m2/year) Fig. 2: Removal Vs loading rates for (A) Ammonia (B) Nitrate (C) MRP
Results and Discussions 20 18 Concentration (mg/L) 16 14 12 10 8 6 4 2 0 Sludge Pond Pond 1 Pond 2 Ammonia Nitrates Phosphate MRP Fig. 3: Leaching water nutrient content
Results and Discussions Fig. 4: Vertical flow to lysimeters
Results and Discussions 0.8 7 0.7 6 Nitrate, MRP (mg/L) (Ammonia (mg/L) 0.6 5 0.5 4 0.4 3 0.3 0.2 2 0.1 1 0.0 0 BH1 BH2 BH3 BH4 BH5 BH6 BH7 BH8 MRP Nitrate Ammonia Fig. 5: Groundwater nutrient content
BH1 BH2 BH4 BH3 General flow BH8 direction is north and may discharge into the river. High ammonia levels BH5 in BH6 and BH7 BH7 might not be coming from the ponds. Further studies required to establish the pollutant source. BH6 Fig. 6: Groundwater head distribution (mOD)
Conclusions ICW are very effective in nutrient removal even at high loading rates. Leaching pond water contain high ammonia levels but nitrate and phosphate are generally low. Low infiltration rate may not constitute immediate threat to groundwater. Low nutrient levels in groundwater except for sample sites that have peat layer in the lithology.
Acknowledgements Dan Doody, Mark Johnston and Eugene Farmer at Monaghan County Council, Ireland. Susan Cook at Waterford County Council, Ireland.
Thank you for your attention Contact: mawuli.dzakpasu@dkit.ie

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Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

  • 1. Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater Society of Wetland Scientists, European Chapter, Annual Meeting 26th May 28th May 2010 Mawuli Dzakpasu1, Oliver Hofmann2, Miklas Scholz2, Rory Harrington3, Siobh叩n Jordan1, Valerie McCarthy1 1 National Centre for Freshwater Studies, Dundalk Institute of Technology, Dundalk, Co. Louth, Ireland. 2Institute for Infrastructure and Environment, School of Engineering, University of Edinburgh, Edinburgh EH9 3JL, UK. 3 Water Services and Policy Division, Department of Environment, Heritage and Local Government, Waterford, Ireland.
  • 2. Presentation Outline Introduction Objectives Materials and methods Results and discussions Conclusions Acknowledgements
  • 3. Introduction Domestic wastewater may contain high levels of nutrients (N & P). Nutrients are significant pollutant sources. National and EU legislation require enhanced management of pollutant sources. Constructed wetlands have been used with rather positive but variable results.
  • 4. Introduction Integrated Constructed Wetlands (ICW) are: Free water surface wetlands. Predominantly shallow emergent vegetated. Multi-celled with sequential through-flow.
  • 5. Introduction The ICW concept explicitly integrates three basic objectives: 1. Sustained capacity to contain and treat water. 2. Landscape fit that enhances site aesthetic and economic values. 3. Enhancing biodiversity and habitats. ICW concept therefore addresses priority areas of the WFD.
  • 6. Introduction Key questions for ICW: Are ICW systems a potential threat to receiving waters? Are local soil materials capable of providing effective protection to underlying and associated groundwater?
  • 7. Research Objectives To evaluate nutrient removal rate in ICW treating domestic wastewater. To estimate rate of infiltration and nutrients leaching through the ICW cell beds. To assess groundwater nutrient concentration near the ICW.
  • 8. Case Study Description Design capacity = 1750 pe. Total area = 6.74 ha Pond water surface = 3.25 ha ICW commissioned Nov. 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
  • 9. Macrophyte Composition at ICW Phragmites australis Carex riparia Typha latifolia Iris pseudacorus Glyceria maxima
  • 10. Overview of ICW Sections Overview of Sludge Pond Overview of Pond 1 Overview of Pond 3 Overview of ICW Outfall Overview of Pond 5
  • 11. Materials and Methods Water Quality Monitoring 1. Wetland water sampling Automated composite samplers at each pond inlet. 24-hour flow-weighted composite samples are taken to determine the mean daily chemical water quality. Grab samples taken for other physical water quality.
  • 12. Materials and Methods 2. Groundwater sampling Eight piezometers placed within ICW. Piezometers placed along suspected flow paths of contaminants. Piezometers are 3-5 m deep. Depth to water ~2 m Samples taken weekly. Water level measured before purging piezometers.
  • 13. Materials and Methods BH1 BH2 BH4 BH3 Sub-soil Geology BH8 Till dominant Alluvium BH7 Peat (mainly near BH3, BH7) BH5 Coefficient of permeability of 9.07x10-11 m/s BH6 Location of piezometers
  • 14. Materials and Methods 3. Leaching water monitoring Gravity pan lysimeters placed below first three ponds. 920 mm diameter. 0.7 m below pond beds. Provide sample of infiltrating water (quantity & quality). Samples collected over 24 hours by attaching bottle to outlet pipe.
  • 15. Materials and Methods L3 L2 L1 L5 L4 L8 L6 L7 Location of lysimeters
  • 16. Materials and Methods Water Quality Analysis Nitrogen: TN, ammonia, nitrate. Phosphorus: TP, MRP. Organic matter: BOD5 ,COD, SS. dissolved oxygen, pH, temperature, redox potential, electrical conductivity, total and faecal coliforms. Analysis done weekly according to Standard methods (APHA, 1998).
  • 17. Results and Discussions Table 1: Influent Composition of ICW ICW Influent Standard Number of Parameter (mean concentrations) Deviation samples COD (mg O2/L) 1178 642.1 101 BOD5 (mg O2/L) 853 552.5 99 Ammonia (mg/L NH4+) 34 10.5 108 Nitrate (mg/L NO3-) 6 5.7 98 Molybdate Reactive 3-) 4 2.3 102 Phosphate (mg/L PO4
  • 18. Results and Discussions Table 2: Effluent Composition from ICW ICW Discharge Standard Number Parameter (mean concentrations) Deviation of samples COD (mg O2/L) 37 26.7 104 BOD5 (mg O2/L) 4.9 5.1 99 TSS (mg/L) 8.9 18.0 100 Ammonia (mg/L NH4+) 0.8 1.7 108 Nitrate (mg/L NO3-) 0.3 0.3 101 Molybdate Reactive 0.03 0.04 100 Phosphate (mg/L PO43-) E. Coli (CFU/100mls) 2 2 5
  • 19. Results and Discussions 120 Removal Efficiency (%) 100 80 60 40 20 0 Ammonia Nitrate Phosphate MRP 2008 2009 Fig. 1: Average annual treatment efficiency of ICW
  • 20. Results and Discussions 200 Removal Rate y = 1.0014x - 0.997 150 (g/m2/year) R族 = 0.9954 100 (A) 50 0 0 50 100 150 200 Loading Rate (g/m2/year) (C) 50 Removal Rate 40 y = 0.9845x - 0.3062 (g/m2/year) R族 = 0.9954 30 20 (B) 10 0 0 10 20 30 40 50 Loading Rate (g/m2/year) Fig. 2: Removal Vs loading rates for (A) Ammonia (B) Nitrate (C) MRP
  • 21. Results and Discussions 20 18 Concentration (mg/L) 16 14 12 10 8 6 4 2 0 Sludge Pond Pond 1 Pond 2 Ammonia Nitrates Phosphate MRP Fig. 3: Leaching water nutrient content
  • 22. Results and Discussions Fig. 4: Vertical flow to lysimeters
  • 23. Results and Discussions 0.8 7 0.7 6 Nitrate, MRP (mg/L) (Ammonia (mg/L) 0.6 5 0.5 4 0.4 3 0.3 0.2 2 0.1 1 0.0 0 BH1 BH2 BH3 BH4 BH5 BH6 BH7 BH8 MRP Nitrate Ammonia Fig. 5: Groundwater nutrient content
  • 24. BH1 BH2 BH4 BH3 General flow BH8 direction is north and may discharge into the river. High ammonia levels BH5 in BH6 and BH7 BH7 might not be coming from the ponds. Further studies required to establish the pollutant source. BH6 Fig. 6: Groundwater head distribution (mOD)
  • 25. Conclusions ICW are very effective in nutrient removal even at high loading rates. Leaching pond water contain high ammonia levels but nitrate and phosphate are generally low. Low infiltration rate may not constitute immediate threat to groundwater. Low nutrient levels in groundwater except for sample sites that have peat layer in the lithology.
  • 26. Acknowledgements Dan Doody, Mark Johnston and Eugene Farmer at Monaghan County Council, Ireland. Susan Cook at Waterford County Council, Ireland.
  • 27. Thank you for your attention Contact: mawuli.dzakpasu@dkit.ie