By: Audella EidAdvisor: Dr. R. Zurayk

Constructed Wetlands for Wastewater treatment

What are constructed wetlands ?

CW are complex, integrated systems

in which water, plants, microorganisms,

and the environment all interact to

improve water quality.

CW have been used in Europe since

the 1960’s.

Municipal wastewater treatment

Acid mine drainage

Agricultural point and non-point discharges

Storm water treatment

Usage of CW

Important Characteristics of CW

Inexpensive

Low-maintenance

Easy operation

High removal efficiencies under various temp, pH, hydraulic and biological loading rates.

Types of CW

Subsurface Flow (SF) wetland

Free-water surface (FWS) wetland

Are earthen basins or channels filled with shallow

water and emergent vegetation.

Wastewater is exposed to the atmosphere.

Recommended for lower strength wastewater,

stormwater treatment or where nitrogen removal is

required.

Free-water surface (FWS)

Subsurface Flow wetland (SF)

Is composed of a cement cell filled with a porous media such as rock or gravel. Wastewater percolated through a porous

medium that supports the root system of the vegetation.

Water flows below the porous surface and is not exposed to the environment.

Recommended for residential homes, schools and

other areas where the exposed wastewater

treatment site may not be suitable.

Decrease chance of exposure, odor and insect

vectors.

SF ( cont’d)

Treatment of wastewater

CW treat wastewater using the following processes:

Filtration

Sedimentation

Physical or chemical immobilization

Chemical and biological decomposition

Absorption and assimilation of excess nutrient by

plants

In each of the two systems march plants aid in:

the treatment of water by improving conditions for

the microorganisms living in the cells.

and by acting as a filter to absorb some trace

metals.

How do they operate?

Plants and microorganisms play a key function

in the cleaning of the wastewater.

Plant roots transpire oxygen and thus aerate the

water.

Large populations of aerobic and anaerobic

bacteria grow within the rhizosphere (which is the

small area surrounding the root zone).

These microbes are the primary source of

treatment, breaking down the complex dissolved

organic and nutrient pollutants into simpler forms that

the plants use as food.

How do they operate?(cont’d1 )

Aerobic conditions in the root zones of the

plants also facilitates growth of large

microorganisms (protozoa) that are essential to

the removal of bacteria, such as fecal

coliforms.

The most common plant used for subsurface

flow is the common reed (Phragmites

australis).

How do they operate?(cont’d2)

The Gharzouz experience

The Gharzouz Reed Bed

The choice of using a constructed wetland for

wastewater treatment was based on:

environmental feasibility social acceptance economic feasibility previous removal efficiencies

Environmental feasibility

The place is relatively

isolated with a lot of land

around it and a large area for

the wetland construction.

The possibility of using the

effluent in irrigating of the

olive and other trees that is

present in the area.

Social acceptance

The community is a

relatively very small

ranging from 15 to 50

people at different times.

They accepted the

implication of this

technique

Economic feasibility

The budget available for

wastewater treatment is

not very high.

The difference in costs

between construction of

a wetland and using a

mechanical method.

Previous removal efficiency

Previous studies that

showed high reduction

rates of BOD , SS and

nitrates.

The previous pilot tests

that were done on this

system (in AUB and other

places in Lebanon) and

proved to be efficient in

reducing BOD and other

measures.

Characteristics of the gravel bed

Constructed

wetland

Area

(m2)

height

(m)

Volume

(m3)

Flow rate

Q

(m3/day)

Retention

time t

(days)

BOD loading

rate

g/m2/day

Cell 1 87 0.7 61 5 4.3 9.6

Cell 2 70 0.7 49 5 3.5 2.5

t= V*Porosity of the gravel bed (assumed to be 35%)/Q&BOD loading rate =Co(avg)*Q /A

MONITORING

Methodology

15 samples of wastewater were collected from

June 1999 till March 2000.

Analysis was carried out using standard method

for COD, BOD, TSS, TDS, Nitrates, Ammonia,

Phosphates, Sulfates, conductivity, pH, Fecal

coliforms, Total Coliforms

RESULTS AND DISCUSSION

COD Removal Rates

437.5335 299

500

730

415

800

2000

720

500

750

550

1000

1800

570

5 20 16 33 35 30 70 15 55 30 40 20 25 95 250

500

1000

1500

2000

2500

July

July

Augus

t

Augus

t

Augus

t

Septe

mbe

r

Septe

mbe

r

Septe

mbe

r

Oct

ober

Novem

ber

Decem

ber

Decem

ber

Janu

ary

Febru

ary

Mar

ch

Samples

inff

lue

nt a

nd e

fflu

ent

va

lue

s (m

g/l)

0102030405060708090100

per

cen

t re

mov

al

influent Effluent 2 COD removal in cell 2

BOD Removal Rates

60

23

159

156178

179183168

202155

188202

148

108

149140159

1333

10 833 29 26

1.4 11 17.5 16

48

18

0

50

100

150

200

250

July

July

Augus

t

Augus

t

Augus

t

Septe

mber

Septe

mber

Septe

mber

Octob

er

Novem

ber

Decem

ber

Decem

ber

Janu

ary

Febru

ary

Mar

ch

Samples

influ

ent

and

eff

luen

t va

lues

(m

g/l)

0.0

20.0

40.0

60.0

80.0

100.0

% p

erce

nt

rem

oval

Influent Effluent 2 Removal in cell 2

Nitrates removal rates

0 0 01.2 0.63

5.45.75

10.7

4.8

8

1111

17

3.23 0.54.7

10.3

1.23 31.62.10.250.951.61.62.61.31.12.3

0

2

4

6

8

10

12

14

16

18

July

July

Augus

t

Augus

t

Augus

t

Septe

mbe

r

Septe

mbe

r

Septe

mbe

r

Oct

ober

Novem

ber

Decem

ber

Decem

ber

Janu

ary

Febru

ary

Mar

ch

Samples

influ

ent

and

eff

lue

nt N

O3

-N

valu

es

(mg/

l)

0

20

40

60

80

100

% p

erc

ern

t re

mo

val

Influent Effluent 2 Nitrates removal in cell 2

Ammonia Removal Rates

2747

66.450

38

118 111

170

217

344

90117.5

203

105.5

211

0

50

100

150

200

250

300

350

400

July

July

Augus

t

Augus

t

Augus

t

Septe

mber

Septe

mber

Septe

mber

Octob

er

Novem

ber

Decem

ber

Decem

ber

Janu

ary

Febru

ary

Mar

ch

Samples

inff

lue

nt a

nd e

fflu

ent

va

lue

s o

f N

H3-

N (

mg/

l)

0

20

40

60

80

100

% p

erc

ent

re

mo

val

Influent Effluent 2 Ammonia removal in cell 2

Phosphate Removal Rate

3 4.6 5.3

0.9

10

1.9 1.74.85

128.5

5

26

4428.3

18

05

101520253035404550

July

July

Augus

t

Augus

t

Augus

t

Septe

mbe

r

Septe

mbe

r

Septe

mbe

r

Oct

ober

Novem

ber

Decem

ber

Decem

ber

Janu

ary

Febru

ary

Mar

ch

Samples

influ

ent

and

eff

lue

nt P

O4

valu

es

(mg/

l)

0

20

40

60

80

100

% p

erc

ent

re

mo

val

Influent Effluent 2 Phosphates removal in cell 2

TSS Removal Rate

140

3660

108

6476

76

148272148

132136128

328180

0

50

100

150

200

250

300

350

July

July

Augus

t

Augus

t

Augus

t

Septe

mbe

r

Septe

mbe

r

Septe

mbe

r

Oct

ober

Novem

ber

Decem

ber

Decem

ber

Janu

ary

Febru

ary

Mar

ch

Samples

TS

S v

alu

es

(mg/

l)

0

20

40

60

80

100

% p

erc

ent

re

mo

val

Influent Effluent 2 SS removal in cell 2

Total Coliform Removal Rate

0

34000

98800

50800

172800

136000

177600

107200

184000

332800

57200

67600

3208069600

103600

0

50000

100000

150000

200000

250000

300000

350000

July

July

Augus

t

Augus

t

Augus

t

Septe

mbe

r

Septe

mbe

r

Septe

mbe

r

Oct

ober

Novem

ber

Decem

ber

Decem

ber

Janu

ary

Febru

ary

Mar

ch

Samples

TC

val

uu

es

(col

onie

s/m

l)

0

20

40

60

80

100

% p

erc

ent

re

mo

val

Influent Effluent 2 Removal rate in cell 2

Fecal Coliform Removal Rate

022000

55200

88400

4240017600 24400

89600

120000

60800

168000163200

251200318000

50000

0

50000

100000

150000

200000

250000

300000

350000

July

July

Augus

t

Augus

t

Augus

t

Septe

mbe

r

Septe

mbe

r

Septe

mbe

r

Oct

ober

Novem

ber

Decem

ber

Decem

ber

Janu

ary

Febru

ary

Mar

ch

Samples

FC

va

lue

s (

colo

nie

s/m

l)

0

20

40

60

80

100

% p

erc

ent

re

mo

val

Influent Effluent 2 Removal rate in cell 2

Comparison of the percent removal rates between previous studies and the current

one

Parameter Currentstudy

Previousstudies

BOD 86 82 - 85

TSS 97 23- 90

Nitrogen 55 54

Ammonia 80 0-70

Phosphorus 89 46

Total coliforms 99.8 35 – 91

Fecalcoliforms

99.9 35 - 90

Comparison between typical performance data and Gharzouz data

Parameter AverageMg/l

TypicalMg/l

COD (Mg/l) 34 < 65

BOD (Mg /L) 23 < 25

P (Mg /L) 1.1 < 1-4

TSS (Mg /L) 4.5 < 15

LIMITATIONS AND CONCERNS

Limitations

Large land area requirements.

Lack of a consensus on design specifications.

Long term effectiveness is not known. Wetland

aging may contribute to a decrease in

contaminant removal rates over time.

When metals are key contaminant, CW do not

destroy them; but only restrict their mobility.

Performance may be more variable and less

predictable than other treatment methods.

Limitations (Cont’d)

COSTS

COSTS

Constructedwetland

MechanicalTreatment

Laborcosts

500 US $

Constructioncosts

4000 US $

Mechanical andcivil works

20,000 US $

yearly maintenance2500 US $

TOTAL4500 US $

TOTAL22,500 US $

The Gharzouz experience indicates that CW

may be an appropriate, low-cost alternative

for small rural communities!

CONCLUSION

THANK YOU