nutrient retention in an integrated constructed wetland used to treat domestic wastewater
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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.
21st Irish Environmental Researchers’ Colloquium
6-8 April, 2011
Presentation outline
• Introduction
o Background
o Objectives
• Case study description
• Materials and methods
• Results
• Conclusions
• Acknowledgements
1
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
Integrated Constructed Wetlands are:
• Multi-celled with sequential through-flow.
• Free water surface flow wetlands.
• Predominantly shallow densely
emergent vegetated.
Background
3
Background
ICW
concept Biodiversity enhancement
ICW conceptual framework
Landscape fit
Water treatment
4
Background
Contaminant removal processes
BIOLOGICAL
PHYSICAL CHEMICAL
TREATED
WATER
INFLUENT
O2 UPTAKE AND TRANSFER
TO ROOT ZONE
5
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.
omodelling kinetics of nutrient removal in the ICW and the influence of water temperature.
6
• 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
Study site description
ICW layout 8
Study site description
Process overview of ICW 9
Materials and methods
• Automated composite
samplers at each pond inlet.
• 24-hour flow-weighted
composite water samples
taken to determine mean
daily chemical quality.
Wetland water sampling regime
10
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
Materials and methods
• Onsite weather station measures
elements of weather.
• Electromagnetic flow meters and allied
data loggers installed at each cell inlet. 12
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
Data analysis and modelling
C* = background concentrations (mg/L);
K = areal first-order removal rate constant (m/yr).
14
Results
ICW water budget
52.9%
47.1%
4.2%
56.7%
14.8%
64 ± 371.3 m3 day-1
139 ± 65.7 m3 day-1 39 ± 27.9 m3 day-1
124 ± 77.8 m3 day-1
149 ± 174.7 m3 day-1
11 ± 9.4 m3 day-1
15
Results
1
10
100
1000F
eb-0
8
May
-08
Au
g-0
8
No
v-0
8
Feb
-09
May
-09
Au
g-0
9
No
v-0
9
Feb
-10
May
-10
Au
g-1
0
No
v-1
0
Feb
-11
Co
nce
ntr
ati
on
(m
g/l
)
BOD influent BOD effluent
0
1
10
Feb
-08
May
-08
Au
g-0
8
No
v-0
8
Feb
-09
May
-09
Au
g-0
9
No
v-0
9
Feb
-10
May
-10
Au
g-1
0
No
v-1
0
Feb
-11
Co
nce
ntr
ati
on
(m
g/l
)
Nitrate influent Nitrate effluent
0.001
0.010
0.100
1.000
10.000
Feb
-08
May
-08
Au
g-0
8
No
v-0
8
Feb
-09
May
-09
Au
g-0
9
No
v-0
9
Feb
-10
May
-10
Au
g-1
0
No
v-1
0
Feb
-11
Co
nce
ntr
ati
on
(m
g/l
)
MRP influent MRP effluent
ICW influent and effluent nutrient concentrations
0
1
10
100
Feb
-08
May
-08
Au
g-0
8
No
v-0
8
Feb
-09
May
-09
Au
g-0
9
No
v-0
9
Feb
-10
May
-10
Au
g-1
0
No
v-1
0
Feb
-11
Co
nce
ntr
ati
on
(m
g/l
)
Ammonia influent Ammonia effluent
16
Results
Results
Nutrient mass loading and removal rates
Variable Loadings (kg/yr) Mass retained
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
Results
Areal first-order kinetic coefficients
for nutrient removal in ICW
Parameter K (m/yr) K20 (m/yr)
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
Results
Seasonal variation of nutrient removal
rate and hydraulic loading rate 19
0
5
10
15
0
20
40
60
80
100
Sp
ring
Su
mm
er
Au
tum
n
Win
ter
Sp
ring
Su
mm
er
Au
tum
n
Win
ter
Sp
ring
Sum
mer
Au
tum
n
Win
ter
2008 2009 2010
HL
R (
mm
/d)
Rem
oval
Rate
(%
)
BOD NH3-N NO3-N PO4-P HLRNH3-N NO3-N BOD5 PO4-P
Rem
ov
al
rate
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
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
We welcome your questions, suggestions, comments!
Thank you for your attention!
26
Contact:
mawuli.dzakpasu@dkit.ie
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