Nutrient Retention in an Integrated Constructed Wetland used to Treat Domestic Wastewater

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:

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