Nitrogen Removal in Integrated Constructed Wetland Treating Domestic Wastewater
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Transcript of Nitrogen Removal in Integrated Constructed Wetland Treating Domestic Wastewater
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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