nutrient leaching and groundwater quality assessment near integrated constructed wetland treating...

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Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater Mawuli Dzakpasu 1 , Oliver Hofmann 2 , Miklas Scholz 2 , Rory Harrington 3 , Siobhán Jordan 1 , Valerie McCarthy 1 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.

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Page 1: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

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.

Page 2: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

Presentation Outline

• Introduction

• Objectives

• Materials and methods

• Results and discussions

• Conclusions

• Acknowledgements

Page 3: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

• 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

Page 4: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

Integrated Constructed Wetlands (ICW) are:

• Multi-celled with sequential through-flow.

• Free water surface wetlands.

• Predominantly shallow emergent vegetated.

Introduction

Page 5: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

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.

Page 6: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

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?

Page 7: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

• 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

Page 8: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

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

Page 9: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

Carex riparia

Phragmites australis

Typha latifolia

Iris pseudacorus

Glyceria maxima

Macrophyte Composition at ICW

Page 10: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

Overview of Sludge Pond

Overview of Pond 3

Overview of Pond 5 Overview of ICW Outfall

Overview of Pond 1

Overview of ICW Sections

Page 11: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

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

Page 12: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

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.

Page 13: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

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

Page 14: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

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

Page 15: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

Materials and Methods

Location of lysimeters

L1 L2

L3

L4

L5

L6

L7

L8

Page 16: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

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

Page 17: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

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

Page 18: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

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

Page 19: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

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

Page 20: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

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

Page 21: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

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

Page 22: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

Results and Discussions

Fig. 4: Vertical flow to lysimeters

Page 23: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

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

Page 24: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

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

Page 25: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

• 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

Page 26: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

Acknowledgements

• Dan Doody, Mark Johnston and

Eugene Farmer at Monaghan

County Council, Ireland.

• Susan Cook at Waterford

County Council, Ireland.

Page 27: Nutrient Leaching and Groundwater Quality Assessment near Integrated Constructed Wetland Treating Domestic Wastewater

Thank you for your attention

Contact:

[email protected]