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

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
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• Onsite weather station measures
elements of weather
• Electromagnetic flow meters and allied
data loggers installed at each cell inlet

15. Data analysis and modelling
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Co = influent concentrations (mg-N/L)
Ce = effluent concentrations (mg-N/L)
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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
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=− (3)
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C* = background concentrations (mg/L);
K = areal first-order removal rate constant (m/yr.)
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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