nutrient leaching and groundwater quality assessment near integrated constructed wetland treating...
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SWS Confab 2010TRANSCRIPT
Nutrient Leaching and Groundwater Quality
Assessment near Integrated Constructed
Wetland Treating Domestic Wastewater
Mawuli Dzakpasu1, Oliver Hofmann2, Miklas Scholz2, Rory Harrington3, Siobhán Jordan1, Valerie McCarthy1
Society of Wetland Scientists, European Chapter, Annual Meeting
26th May – 28th May 2010
1 National Centre for Freshwater Studies, Dundalk Institute of Technology, Dundalk, Co. Louth, Ireland. 2 Institute for Infrastructure and Environment, School of Engineering, University of Edinburgh, Edinburgh EH9 3JL, UK. 3 Water Services and Policy Division, Department of Environment, Heritage and Local Government, Waterford, Ireland.
Presentation Outline
• Introduction
• Objectives
• Materials and methods
• Results and discussions
• Conclusions
• Acknowledgements
• Domestic wastewater may contain high levels
of nutrients (N & P).
• Nutrients are significant pollutant sources.
• National and EU legislation require enhanced
management of pollutant sources.
• Constructed wetlands have been used with
rather positive but variable results.
Introduction
Integrated Constructed Wetlands (ICW) are:
• Multi-celled with sequential through-flow.
• Free water surface wetlands.
• Predominantly shallow emergent vegetated.
Introduction
Introduction
• The ICW concept explicitly integrates three basic
objectives:
1. Sustained capacity to contain and treat water.
2. Landscape fit that enhances site aesthetic and
economic values.
3. Enhancing biodiversity and habitats.
• ICW concept therefore addresses priority areas of the
WFD.
Introduction
Key questions for ICW:
• Are ICW systems a potential threat to receiving
waters?
• Are local soil materials capable of providing effective
protection to underlying and associated groundwater?
• To evaluate nutrient removal rate in ICW
treating domestic wastewater.
• To estimate rate of infiltration and nutrients
leaching through the ICW cell beds.
• To assess groundwater nutrient concentration
near the ICW.
Research Objectives
Case Study Description
• Design capacity = 1750 pe.
• Total area = 6.74 ha
• Pond water surface = 3.25 ha
• ICW commissioned Nov. 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
Carex riparia
Phragmites australis
Typha latifolia
Iris pseudacorus
Glyceria maxima
Macrophyte Composition at ICW
Overview of Sludge Pond
Overview of Pond 3
Overview of Pond 5 Overview of ICW Outfall
Overview of Pond 1
Overview of ICW Sections
Water Quality Monitoring
1. Wetland water sampling
• Automated composite samplers
at each pond inlet.
• 24-hour flow-weighted
composite samples are taken to
determine the mean daily
chemical water quality.
• Grab samples taken for other
physical water quality.
Materials and Methods
Materials and Methods
2. Groundwater sampling
• Eight piezometers placed within ICW.
• Piezometers placed along suspected
flow paths of contaminants.
• Piezometers are 3-5 m deep.
• Depth to water ~2 m
• Samples taken weekly.
• Water level measured before purging
piezometers.
Materials and Methods BH1
BH2
BH3
BH4
BH5
BH6
BH7
Location of piezometers
Sub-soil Geology
• Till – dominant
• Alluvium
• Peat (mainly near BH3, BH7)
• Coefficient of permeability
of 9.07x10-11 m/s
BH8
3. Leaching water monitoring
• Gravity pan lysimeters placed
below first three ponds.
• 920 mm diameter.
• 0.7 m below pond beds.
• Provide sample of infiltrating water
(quantity & quality).
• Samples collected over 24 hours by
attaching bottle to outlet pipe.
Materials and Methods
Materials and Methods
Location of lysimeters
L1 L2
L3
L4
L5
L6
L7
L8
Water Quality Analysis
• Nitrogen: TN, ammonia, nitrate.
• Phosphorus: TP, MRP.
• Organic matter: BOD5 ,COD, SS.
dissolved oxygen, pH, temperature, redox
potential, electrical conductivity, total and faecal
coliforms.
• Analysis done weekly according to
Standard methods (APHA, 1998).
Materials and Methods
Results and Discussions
Table 1: Influent Composition of ICW
Parameter ICW Influent
(mean concentrations)
Standard
Deviation
Number of
samples
COD (mg O2/L) 1178 642.1 101
BOD5 (mg O2/L) 853 552.5 99
Ammonia (mg/L NH4+) 34 10.5 108
Nitrate (mg/L NO3-) 6 5.7 98
Molybdate Reactive
Phosphate (mg/L PO43-)
4 2.3 102
Results and Discussions
Table 2: Effluent Composition from ICW
Parameter ICW Discharge
(mean concentrations)
Standard
Deviation
Number
of samples
COD (mg O2/L) 37 26.7 104
BOD5 (mg O2/L) 4.9 5.1 99
TSS (mg/L) 8.9 18.0 100
Ammonia (mg/L NH4+) 0.8 1.7 108
Nitrate (mg/L NO3-) 0.3 0.3 101
Molybdate Reactive
Phosphate (mg/L PO43-)
0.03 0.04 100
E. Coli (CFU/100mls) 2 2 5
Results and Discussions
0
20
40
60
80
100
120
Ammonia Nitrate Phosphate
Rem
ov
al
Eff
icie
ncy
(%
)
2008 2009
Fig. 1: Average annual treatment efficiency of ICW
MRP
Results and Discussions
y = 1.0014x - 0.997
R² = 0.9954
0
50
100
150
200
0 50 100 150 200
Rem
ov
al
Ra
te
(g/m
2/y
ear)
Loading Rate (g/m2/year)
y = 0.9845x - 0.3062
R² = 0.9954
0
10
20
30
40
50
0 10 20 30 40 50
Rem
ov
al
Ra
te
(g/m
2/y
ear)
Loading Rate (g/m2/year)
(C)
(A)
(B)
Fig. 2: Removal Vs loading rates for (A) Ammonia (B) Nitrate (C) MRP
0
2
4
6
8
10
12
14
16
18
20
Sludge Pond Pond 1 Pond 2
Co
nce
ntr
ati
on
(m
g/L
)
Ammonia Nitrates Phosphate
Fig. 3: Leaching water nutrient content
Results and Discussions
MRP
Results and Discussions
Fig. 4: Vertical flow to lysimeters
Fig. 5: Groundwater nutrient content
Results and Discussions
0
1
2
3
4
5
6
7
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
BH1 BH2 BH3 BH4 BH5 BH6 BH7 BH8
(Am
mo
nia
(m
g/L
)
Nit
rate
, M
RP
(m
g/L
)
MRP Nitrate Ammonia
Fig. 6: Groundwater head distribution (mOD)
• General flow
direction is north and
may discharge into
the river.
• High ammonia levels
in BH6 and BH7
might not be coming
from the ponds.
• Further studies
required to establish
the pollutant source.
BH7 BH5
BH6
BH4
BH2
BH1
BH3
BH8
• ICW are very effective in nutrient removal even at
high loading rates.
• Leaching pond water contain high ammonia levels
but nitrate and phosphate are generally low.
• Low infiltration rate may not constitute immediate
threat to groundwater.
• Low nutrient levels in groundwater except for
sample sites that have peat layer in the lithology.
Conclusions
Acknowledgements
• Dan Doody, Mark Johnston and
Eugene Farmer at Monaghan
County Council, Ireland.
• Susan Cook at Waterford
County Council, Ireland.