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Presentation at 2nd Irish International Conference on Constructed Wetlands for Wastewater Treatment & Environmental Pollution Control. 1-2 Oct. 2010
Citation preview
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. 2 Institute 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.
2nd Irish International Conference on Constructed Wetlands for
Wastewater Treatment and Environmental Pollution Control
1st – 2nd October 2010
Presentation outline
• Introduction
o Background
o Aim and objectives
• Case study description
• Materials and methods
• Results
• Conclusions
• Acknowledgements
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
Background
Integrated Constructed Wetlands (ICW) are:
• Multi-celled with sequential through-flow
• Free water surface flow wetlands
• Predominantly shallow densely
emergent vegetated
Background
ICW
concept Biodiversity enhancement
ICW conceptual framework
Landscape fit
Water treatment
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
Background
Nitrogen biogeochemical cycle in wetlands
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
Case study description
Location map of ICW site
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
Case study description
Process overview of ICW
• Automated composite
samplers at each pond inlet
• 24-hour flow-weighted
composite water samples
taken to determine mean
daily chemical quality
Materials and methods
Wetland water sampling regime
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
Materials and methods
Wetland hydrology
• 𝑄𝑖 − 𝑄𝑜 + 𝑄𝑐 + (𝑃 − 𝐸𝑇 − 𝐼)𝐴 =𝑑𝑉
𝑑𝑡
• Onsite weather station measures
elements of weather
• Electromagnetic flow meters and allied
data loggers installed at each cell inlet
Data analysis and modelling
𝑅𝑒𝑚𝑜𝑣𝑎𝑙 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = 𝐶𝑜 − 𝐶𝑒
𝐶𝑜× 100 (1)
𝐴𝑟𝑒𝑎𝑙 𝑅𝑒𝑚𝑜𝑣𝑎𝑙 𝑅𝑎𝑡𝑒 = 𝑞 × 𝐶𝑜 − 𝐶𝑒 (2)
𝑤ℎ𝑒𝑟𝑒:
𝑞 =𝑄
𝐴 and 𝑄 = 𝑄𝑖𝑛 + 𝑃 − 𝐸𝑇 − 𝐼 𝐴
Co = influent concentrations (mg-N/L)
Ce = effluent concentrations (mg-N/L)
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)
Data analysis and modelling
𝐼𝑛𝐶𝑒 − 𝐶∗
𝐶𝑜 − 𝐶∗= −
𝐾
𝑞 (3)
𝐾(𝑡) = 𝐾(20)𝜃(𝑡−20) (4)
log 𝐾 𝑡 = log 𝜃 𝑡 − 20 + log 𝐾 20 (5)
C* = background concentrations (mg/L);
K = areal first-order removal rate constant (m/yr.)
K(t) and K(20) = first-order removal rate constants (m/yr.);
t = temperature (oC); 𝜃 = empirical temperature coefficient
Results
Average rainfall and wastewater discharge at ICW
influent and effluent points (April, 2008 – May, 2010)
0
50
100
150
200
250
0
50
100
150
200
250
300
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Ra
infa
ll (
mm
/mon
th)
Dis
cha
rge
(m3/d
ay
)
Influent Effluent Rainfall
Materials and methods
ICW water budget
55.8 ± 11.3%
44.2 ± 11.3%
5.3 ± 2.7%
49.8 ± 23.3%
24.6 ± 12.7%
63 ± 371.3 m3 day-1
139 ± 65.7 m3 day-1 39 ± 27.9 m3 day-1
123 ± 61.8 m3 day-1
106 ± 112.2 m3 day-1
11 ± 9.4 m3 day-1
Nitrogen removal with cumulative wetland area
Results
0
1
10
100
0% 1% 15% 29% 68% 96% 100%
Influent Sludge
pond
Pond 1 Pond 2 Pond 3 Pond 4 Pond 5
Nit
rogen
(m
g-N
/L)
Ammonia Nitrate
1
10
100
Summer Autumn Winter Spring Summer Autumn Winter
2008 2009
Nit
rogen
(m
g-N
/L)
Ammonia Nitrate
* * *
* * *
*
Seasonal variations of influent nitrogen to ICW * Indicates significant seasonal variation (P < 0.01, n = 18)
Results
0
1
10
Summer Autumn Winter Spring Summer Autumn Winter
2008 2009
Nit
rogen
(m
g-N
/L)
Ammonia Nitrate
Seasonal variations of effluent nitrogen from ICW * Indicates significant seasonal variation (P < 0.01, n = 18)
* * *
* * *
*
Results
0
2
4
6
8
10
12
0
20
40
60
80
100
Summer Autumn Winter Spring Summer Autumn Winter
2008 2009
HL
R (
mm
/d)
Rem
ov
al
Eff
iien
cy (
%)
Ammonia Nitrate HLR
Seasonal variations of nitrogen removal
efficiency and hydraulic loading rate
Results
y = 0.988x - 1.551
R² = 0.99
0
600
1200
1800
0 600 1200 1800
Rem
oval
Rate
(mg m
-2 d
-1)
Loading Rate (mg m-2 d-1)
a) Ammonia
y = 0.952x - 0.111
R² = 0.99
0
250
500
750
1000
0 250 500 750 1000
Rem
oval
Rate
(mg m
-2 d
-1)
Loading Rate (mg m-2 d-1)
b) Nitrate
Areal nitrogen loading and removal rates
Results
Areal first-order nitrogen removal rate
constants in ICW
Parameter
K (m/yr) K20 (m/yr)
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
Results
y = -0.081x + 15.56
R² = 0.0004
0
60
120
0 5 10 15 20 25
KA (
m/y
r)
Water temperature (oC)
y = -0.098x + 11.98
R² = 0.0009
0
40
80
0 5 10 15 20 25
KN (
m/y
r)
Water temperature (oC)
Water temperature and reaction rate constants
(a) Ammonia
(b) Nitrate
Results
y = 0.05x + 2.23
R² = 0.77
0
60
120
0 500 1000 1500 2000
KA (
m/y
r)
Loading rate (mg m-2 d-1)
y = 0.09x + 4.23
R² = 0.66
0
50
100
0 200 400 600 800 1000
KN (
m/y
r)
Loading rate (mg m-2 d-1)
(a) Ammonia
(b) Nitrate
Nitrogen loading rate and reaction rate constants
Results
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
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.
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