SWS Confab 2010

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, 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.

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)
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

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