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

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SWS Confab 2010

SWS Confab 2010

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

  • 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, Siobhán 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) R² = 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) R² = 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