This document summarizes a study on nutrient retention in an integrated constructed wetland used to treat domestic wastewater. The study evaluated nutrient removal over 3 years of full-scale operation, establishing a water balance and comparing annual and seasonal nutrient removal rates. Results showed removal rates consistently over 90% for parameters like BOD5, NH3-N, NO3-N, and PO4-P. Removal rates were slightly influenced by seasonality and hydrological regime. Temperature coefficients indicated slight temperature dependence. The constructed wetland effectively treated wastewater and retained nutrients.

1. 21st Irish Environmental Researchers’ Colloquium
6-8 April, 2011
Nutrient Retention in an Integrated Constructed
Wetland used to Treat Domestic Wastewater
Mawuli Dzakpasu1 , Oliver Hofmann2, Miklas Scholz3,
Rory Harrington4, Siobhán Jordan1, Valerie McCarthy1
1 Centre for Freshwater Studies, Dundalk Institute of Technology, Dundalk, Co. Louth, Ireland.
2 School of the Built Environment, Edinburgh Napier University, Edinburgh EH10 5DT, UK
3 Civil Engineering Research Group, the University of Salford, Newton Building, Salford M5 4WT, UK.
4 Water and Environment section, Waterford County Council, Kilmeadan, Co. Waterford, Ireland.

2. Presentation outline
• Introduction
o Background
o Objectives
• Case study description
• Materials and methods
• Results
• Conclusions
• Acknowledgements
1

3. Background
• Constructed wetlands are used to treat several
categories of wastewater worldwide.
• Nutrient removal efficiencies are generally
lower and more variable.
• Irish integrated constructed wetlands (ICW)
concept has developed over last decade.
2

4. Background
Integrated Constructed Wetlands are:
• Free water surface flow wetlands.
• Predominantly shallow densely
emergent vegetated.
• Multi-celled with sequential through-flow.
3

5. Background
Water treatment
ICW
Landscape fit concept Biodiversity enhancement
ICW conceptual framework 4

6. Background
O2 UPTAKE AND TRANSFER
TO ROOT ZONE
INFLUENT CHEMICAL
PHYSICAL
TREATED
BIOLOGICAL WATER
Contaminant removal processes 5

7. Objectives
• To evaluate nutrient removal in ICW over a 3-year
full-scale operation by:
o establishing a water balance of the system, using
hydrological variables of inflow, outflow,
precipitation, evapotranspiration, runoff, storage,
and assess its effects on nutrient treatment.
o comparing annual and seasonal nutrient removal
rates of the ICW.
o modelling kinetics of nutrient removal in the
ICW and the influence of water temperature.
6

8. Study site description
• Total area = 6.74 ha
• Pond water surface = 3.25 ha
• Commissioned Oct. 2007
• 1 pump station
• 2 sludge ponds
• 5 vegetated cells
• Natural local soil liner
• Current load = 800 pe.
• Mixed black and grey water
ICW layout 8

9. Study site description
Process overview of ICW 9

10. 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.
10

11. Materials and methods
Water quality analysis
• Water samples analysed for NH3-N,
NO3-N and PO4-P using HACH
spectrophotometer DR/2010 49300-22.
• N-allylthiourea BOD5 determined with
WTW GmbH OxiTop system.
• Dissolved oxygen, temperature, pH, redox
potential measured with WTW GmbH
portable multiparameter meter. 11

12. Materials and methods
• Onsite weather station measures
elements of weather.
• Electromagnetic flow meters and allied
data loggers installed at each cell inlet. 12

13. Data analysis and modelling
Ci and Ce= influent and effluent nutrient concentrations (mg/L),
Qi and Qe = influent and effluent volumetric flow rate of water (m3/d).
q = hydraulic loading rate (m/yr); Q = volumetric flow rate in
wetland (m3/d); A = wetland area (m2); P = precipitation rate (m/d);
ET = evapotranspiration rate (m/d); I = infiltration rate (m/d).
13

14. Data analysis and modelling
C* = background concentrations (mg/L);
K = areal first-order removal rate constant (m/yr).
14

15. Results
39 ± 27.9 m3 day-1 139 ± 65.7 m3 day-1
14.8% 52.9%
124 ± 77.8 m3 day-1
47.1%
149 ± 174.7 m3 day-1
64 ± 371.3 m3 day-1 56.7%
4.2%
11 ± 9.4 m3 day-1
ICW water budget 15

16. Concentration (mg/l) Concentration (mg/l)
10
0
1
10
1000
1
100
Feb-08
Feb-08
May-08
May-08
Aug-08
Aug-08
Nov-08
Nov-08
Feb-09
Results
Nitrate influent
BOD influent
Feb-09
May-09
May-09
Aug-09 Aug-09
Nov-09 Nov-09
Feb-10 Feb-10
May-10 May-10
BOD effluent
Aug-10 Aug-10
Nitrate effluent
Nov-10 Nov-10
Feb-11 Feb-11
Concentration (mg/l) Concentration (mg/l)
10
0
1
100
Results
0.001
0.010
0.100
1.000
10.000
Feb-08
Feb-08 May-08
May-08 Aug-08
Aug-08 Nov-08
Nov-08 Feb-09
MRP influent
Ammonia influent
Feb-09
May-09
May-09
Aug-09
Aug-09
Nov-09
Nov-09
Feb-10
Feb-10
May-10 May-10
Aug-10
MRP effluent
Aug-10
16
Nov-10 Nov-10
Ammonia effluent
ICW influent and effluent nutrient concentrations
Feb-11 Feb-11

17. Results
Nutrient mass loading and removal rates
Loadings (kg/yr) Mass retained
Variable
Influent Effluent (%) (kg/yr)
BOD5 8275.8 123.3 98.5 8152.4
NH3-N 1025.5 42.2 92.4 983.4
NO3-N 116.8 9.7 88.4 107.1
PO4-P 110.3 6.5 94.3 103.9
17

18. Results
Areal first-order kinetic coefficients
for nutrient removal in ICW
K (m/yr) K20 (m/yr)
Parameter θ
Mean SD n Mean SD n
BOD5 10.5 6.69 194 9.3 5.96 194 0.982
NH3-N 10.0 7.34 204 13.2 9.11 204 1.025
NO3-N 6.0 4.47 195 5.3 3.97 195 0.979
PO4-P 9.5 8.53 197 12.7 11.04 197 1.026
18

19. Results
100 15
Removal Rate (%)
80
HLR (mm/d)
Removal rate
10
60
40
5
20
0 0
Autumn
Autumn
Autumn
Summer
Summer
Summer
Spring
Spring
Spring
Winter
Winter
Winter
2008 2009 2010
BOD5
BOD NH3-N
NH3-N NO3-N
NO3-N PO4-P
PO4-P HLR
Seasonal variation of nutrient removal
rate and hydraulic loading rate 19

20. Conclusions
• Removal rates consistently > 90 %.
• Removal rates slightly influenced by seasonality.
• Removal rates influenced by hydrological regime.
• Slightly minimal temperature coefficients indicate
slight temperature dependence.
20

21. Acknowledgements
• Monaghan County Council, Ireland for funding
the research.
• Dan Doody, Mark Johnston and Eugene Farmer
at Monaghan County Council and Susan Cook at
Waterford County Council for technical support.
21

22. Thank you for your attention!
We welcome your questions,
suggestions, comments!
Contact:
mawuli.dzakpasu@dkit.ie 26