Analyzing Remediation Potential of Wastewater

Through Wetland Plants: A ReviewMisha Bhatia and Dinesh GoyalDepartment of Biotechnology, Thapar University, Patiala 147004, Punjab, India; dgoyal@thapar.edu (for correspondence)

Published online 00 Month 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ep.11822

Treatment of different wastewater using macrophytes-vegetated constructed wetland reveals its potential in terms ofsignificant reduction in BOD, COD, suspended solids, totalsolids, total nitrogen, heavy metals along with remediation ofxenobiotics, pesticides and polyaromatic hydrocarbons. Therhizosphere of macrophytes such as Phragmites, Typha,Juncus, Spartina and Scirpus serves as an active and dynamiczone for the microbial degradation of organic and sequestra-tion of inorganic pollutant resulting in successful treatment ofdomestic, textile and other effluents. Up to 2049–6648 mgmetal per gram dry weight of plant biomass are found toaccumulate in plant parts i.e. shoots and roots. Major metalremoval mechanisms are bioaccumulation in plant parts, phy-toextraction and phytostabilization. Different wastewaterstreated through this technology are industrial, domestic, dairy,pesticides, PAHs, and xenobiotics containing effluents. Load-ing limits of the wetland, removal efficiency, biomass disposaland variation in seasonal growth are some of the limiting fac-tors which can be overcome by stimulating the plant microbeinteraction through designer rhizospheres involving pigmenta-tion, biostimulation and genetic alterations of plant and asso-ciated microbial community. VC 2013 American Institute of

Chemical Engineers Environ Prog, 00: 000–000, 2013

Keywords: wastewater, bioaugmentation, designer rhizo-spheres, biostimulation, constructed wetlands

INTRODUCTION

Comprising over 70% of the Earth’s surface, water is themost precious natural resource that exists on our planet [1].Most water pollutants are eventually carried by rivers into thelarge water bodies no longer leaving them clean or pure; pos-ing human health risks. Water is referred to as polluted whenit is impaired by anthropogenic contaminants and either doesnot support a human use (like serving as drinking water) orundergoes a marked shift in its ability to support its constitu-ent biotic communities [2]. For water pollution two generalcategories exist: direct and indirect. The former include efflu-ent outfalls from factories, refineries, and waste treatmentplants etc., that emits fluid of varying quality directly intourban water supplies. The latter includes contaminants thatenter the water supply from soil= groundwater systems andfrom the atmosphere via rain water. Soils and ground waterscontain the residue of human agricultural practices (fertilizers,pesticides, etc.) and improperly disposed of industrial wastes[3]. Some major pollutants found in contaminated waters areheavy metals, xenobiotics, nutrients, organic matter and acidi-fying gases such as sulfur dioxide. The discharge of effluent

from domestic and industrial sources has detrimental effectson the aquatic ecosystem [4] as this outfall can deposit largeamount of organic matter, nutrients and pollutants leading toeutrophication (fertilization of surface water by nutrients thatwere previously scarce), temporary oxygen deficits and accu-mulation of pollutants into receiving waterways.

In the last few decades, researchers have tried to adoptan eco-technological approach to clean up or remediatewastewater using plants. This use of plants termed phytore-mediation (phyto meaning plant and remedium meaning toclean or restore) actually refers to diverse collection of natu-ral or genetically engineered plants for cleaning contami-nated environments [5]. Eventually combining the existingbiological and engineering strategies to improve the applic-ability of phytoremediation has come up in the form of con-structed wetlands (CW) using plants termed macrophyteswhich according to USEPA are aquatic plants, growing in ornear water that are emergent, submergent, or floating. Pres-ent review aims to sum up different aspects of constructedwetlands, design, construction and its applications for treat-ing various effluents. Some attempts to improve the modelsystem using novel techniques are also discussed.

CONSTRUCTED WETLANDS

The Ramsar convention brought wetlands to the attention ofthe world and proposed the following definition: Wetlands areareas of marsh, fern, peat land or water whether natural or artifi-cial, permanent or temporary, with water that is static or flowing,fresh, brackish or salt, including areas of marine water the depthof which at low tide does not exceed 6 m [6]. Constructed wet-lands are complex biological system that mimics natural self-cleansing processes [7] by reducing pollutant level to a dis-chargeable limit. In fact these can be treated as nature’s kidneys.Root morphology and depth are important plant characteristicsfor phytoremediation. A fibrous root system (found in grassese.g., Fescue), has numerous fine roots spread throughout thesoil and provides maximum contact with the soil due to the highsurface area of the roots. A tap root system (such as in alfalfa) isdominated by one larger central root. Root depth directlyimpacts the depth of soil that can be remediated or depth ofground water that can be influenced, as close contact is neededbetween the root and the contaminant or water [8]. Some com-mon plants used in wetlands are listed below in Table 1.

A universally used plant species is Phragmites [30,31]commonly called reeds, which contribute to wastewatercleaning processes in many different ways: increasing thepermeability and porosity of substrate [32], creating microsites with reducing conditions by releasing oxygen from theroots [33,34] termed as ROL (Radial oxygen loss). Throughthese oxygenated and oxygen poor micro sites even resistantVC 2013 American Institute of Chemical Engineers

Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep July 2013 1

chemicals get affected [32]. The withered parts insulate theroot zone during the cold period. So in the temperate cli-mates the pollutant removal capacity is affected only slightlythe seasons [35]. Actually, the plant forms a thick root-mass,and by virtue of aerial stems transports oxygen to the rootzone, thus aiding microbial activity and microbial digestion.

A typical system can be divided into three sections: inlet,vegetation and outlet. Prior to inlet section is a presettlementtank with a continuous inflow. Vegetation section, the princi-pal component of constructed wetlands is composed ofplants having the ability to accumulate some compounds inlarge concentration as compared to environment and alsoremoves nutrients in wetlands [36–39]. It is composed ofgravel bed on sides and inside planted with macrophyteswhich lead to outlet section connected to the collection tank.HSSF (Horizontal subsurface flow) and VSSF (Vertical subsur-face flow) and hybrid system (using is the combination of avertical and horizontal flow subsurface) constructed wetlandor a acombination of any two concepts provides a means formore effective treatment efficiency [39].

Remediation ProcessOften termed green remediation, botano-remediation,

agro-remediation, vegetative remediation, it involves a con-tinuum of processes each occurring to differing degrees fordifferent conditions, media, contaminants, and plants [8].Five main processes have been identified in remediation pro-cess: Phytoextraction [40], Phytodegradation [41], Rhizofiltra-tion [42], Phytostabilization [43], Phytovolatilization [44,45].These processes tend to overlap to some degree and occurin varying proportions during phytoremediation [8].

Bioremediation using plants has been naturally coupledwith microbial remediation in the form of rhizospheric bacte-ria termed as “rhizoremediation”, where organics and nutri-ent removal is mostly performed by attached micro biota[34]. Rhizoremediation involves interactions of plant rootsand associated microbes to remediate elevated concentra-tions of some compounds; present as solid, liquid or gaseoussubstrates [46]. Such interactions offer very useful means fortreating water contaminated with recalcitrant organic com-pounds [47]. The success of a plant species as the spot of rhi-

zoremediation depends on (1) highly branched root systemto harbor large number of bacteria, (2) primary and second-ary metabolism, and (3) establishment, survival, and ecologi-cal interactions with other organisms [48]. Some co-metabolized (Cometabolism is defined as the oxidation ofnon growth substrates during the growth of an organism onanother carbon or energy source) recalcitrant pollutants suchas pesticides are only transformed and not effectively miner-alized by microorganisms [49]. Microbes living in the rhizo-sphere termed rhizomicrobia also promote plant health bystimulating root growth (regulators), enhancing water andmineral uptake and inhibiting growth of pathogenic andnon-pathogenic soil microbes [46,48]. Rhizomicrobia mayalso accelerate remediation processes by volatilizing organicssuch as PAHs or by increasing the humification of organicpollutants [50].

The rhizosphere of plants acts as a microcosm wheremicrobial activity is enhanced leading to active degradationof recalcitrant compounds and reduction in parameters likeBOD (Biological Oxygen Demand), COD (Chemical OxygenDemand), TS (Total Solids), and salt level from various efflu-ents like acid mine drainage, agricultural landfill and urbanstorm-water runoff. Some contaminants are also released intothe environment as a result of spills of fuel and solvents,military explosives, chemical weapons, agricultural uses (pes-ticides, herbicides), industrial (chemical, petrochemical), andwood treatment activities and get degraded in the root zoneof plants or taken up, followed by sequestration or volatiliza-tion. Organic pollutants that have been successfully phytore-mediated include organic solvents, for example,trichloroethylene [51], herbicides like atrazine [52], explosivessuch as trinitrotoluene, petroleum hydrocarbons, oil, gaso-line, BTEX [53], monoaromatic hydrocarbons, and PAHs, pol-yaromatic hydrocarbons, MTBE, PCBs [54]. Inorganicpollutants mostly occur as natural elements and human activ-ities such as mining and traffics promote their release intothe environment, leading to toxicity. Inorganics like planttrace elements (Cr and Zn), non-essential elements (Cd andHg) and radioactive isotopes cannot be degraded but aretransformed via stabilization or sequestration in harvestableplant tissues [46] as shown in Table 2.

Table 1. List showing common macrophytes used in constructed wetlands

Family Plant Common name Reference

Poaceae Poa pratensis Kentucky Bluegrass [9]Phragmites spp. Reed [10–12]Oryza sativa Common rice [13]Paspalum distichum Knotgrass [11]Phalaris arundinacea Reed canary grass [14]Glyceria fluitans Floating Sweet-grass [14]Spartina spp. Coralgrass [15]

Cyperaceae Schoenoplectus spp. Club-rush [16]Cyperus spp Papyrus sedges [16]Carex spp. Sedges [17]Scirpus spp Bullrush [18,19]

Salicaceae Populus spp Poplar Trees [20]Salix spp Willow Trees [20]

Typhaceae Sparganium erectum Bur-reed [14]Typha latifolia Cattail [21]

Alismataceae Sagittaria spp. Common Arrowhead [22]Amaranthaceae Kochia spp Forage Kochia [23]Ceratophyllaceae Ceratophyllum spp. Coontail [24]Fabaceae Medicago sativa Alfalfa [9]Junaceae Juncus spp. Rush [25]Lemnaceae Lemna minor Duckweed [26,27]Pontederiaceae Eichhornia crassipes Water Hyacinths [27,28]Potamogetonaceae Potamogeton spp. American pondweed [29]

Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep2 July 2013

Tab

le2.Rem

edia

tion

pote

ntial

ofdiffe

rentm

eta

lsusi

ng

wetlan

dpla

nts

Meta

lVegeta

ted

pla

nts

Rem

oval

mech

an

ism

Rem

oval

stati

stic

sC

ase

stu

dy

Refe

ren

ces

Pb,Cd

Typ

ha

dom

inge

nsi

s,Le

mm

am

inor

Bio

accu

mula

tion

by

pla

nts

Pote

ntial

meta

lre

moval

rate

sar

e3–8

mg

Pb=m

2day

and

2–4

mg

Cd=m

2day

Wetlan

dm

icro

cosm

s[2

6]

Zn,Pb,Cd

Ph

ragm

ites

Meta

lto

lera

nce

,upta

ke

and

accu

mula

tion

Zn

insh

oots

:47

2049mg

g2

1

d.w

tZn

inro

ots

:100–6684mg

g2

1d.w

tPb

insh

oots

:2.5

–80mg

g2

1

d.w

tPb

inro

ots

:8.4

–830mg

g2

1

d.w

tCd

insh

oots

:0.3

–7.4

mgg

21

d.w

tCd

inro

ots

:2.5

–49mg

g2

1

d.w

t

Meta

lac

cum

ula

tion

inse

ed-

lings

from

two

diffe

rent

sourc

es

under

gla

ss-h

ouse

conditio

ns

[10]

Zn,Pb,Cd

Typ

ha

lati

foli

aH

eav

ym

eta

lupta

ke

Leav

es:

Zn:22–122,Pb:4–7–

40

and

Cd:0

–2–0–8==g

g~d.

wt

Soil-s

edim

ents

:Zn:86–3009,

Pb:26–18894

and

Cd:l–

4–

26==gg-i

d.w

tRoots

:Zn:46–946,Pb:25–

3628

and

Cd:10–17==g

gd.w

t

Seedlings

were

gro

wn

inth

em

eta

ltreat

mentso

lutions

or

inth

em

eta

l-co

nta

min

ated

media

under

labora

tory

conditio

ns

[10]

Cu

Ph

ragm

ites

au

stra

lis

Phyto

extrac

tion

Bio

conce

ntrat

ion

fact

or

(BCF)

incr

eas

ed

from

349

to1931

on

incr

eas

ing

Copper

con-

centrat

ion

from

7.8

5to

78.5

mm

Hydro

ponic

experim

entat

dif-

fere

ntCu

conce

ntrat

ions

[55]

Zn,Pb

Typ

ha

Acc

um

ula

tion

intiss

ues,

pre

cipitat

ion

asiron-

hydro

xid

es

inro

ot

zones

0–99%

and

0–64%

reduct

ion

for

Zn

and

Pb,re

spect

ively

,in

pond

1an

d94–99%

for

Zn

and

25–6

0%

for

Pb

inpond

2,69%

rem

oval

rate

sofsu

lfat

ein

eac

h

Series

ofsu

bsu

rfac

eflow

ponds

filled

with

spent

mush

room

subst

rate

con-

stru

cted

atN

avan

,Ir

ela

nd

[56]

Cu

Scir

pu

sca

lifo

rnic

us

Copper

imm

obiliz

atio

nin

wetlan

dSh

oots

and

roots

of

S.ca

lifo

r-n

icu

sso

rbed

0.6

%an

d1.9

%,re

spect

ively

,ofco

p-

per

ente

ring

the

syst

em

Eig

ht-ac

reco

nst

ruct

ed

wetlan

dtreat

mentsy

stem

rece

ivin

gco

pper-

conta

min

ated

wat

er

[19]

N,P

Ph

ragm

ites

N-

reduct

ion,P-

imm

o-

biliz

atio

n,physi

cal

settle

mentofso

lids

51%

reduct

ion

for

tota

lN

,13%

tota

lP,

84–90%

for

sus-

pended

solids

and

49%

for

BO

D

Const

ruct

ed

surf

ace

flow

wet-

lands

atIr

ela

nd

[57]

Cu

Ph

ragm

ites

au

stra

lis

Meta

lto

lera

nce

,U

pta

ke,

Acc

um

ula

tion

Cu

conce

ntrat

ions

inth

ePM

shoots

were

hig

her

than

inth

eFS,

WB

and

PB

shoots

,butlo

wer

than

inth

eH

Ksh

oots

Tw

om

ine

site

s(P

arys

UK

and

Belg

ium

)conta

min

ated

with

Cu

and

thre

e‘c

lean

’si

tes

(UK

,H

ong

Kong)w

ere

[58]

Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep July 2013 3

Tab

le2.

Con

tin

ued

Meta

lV

egeta

ted

pla

nts

Rem

oval

mech

an

ism

Rem

oval

stati

stic

sC

ase

stu

dy

Refe

ren

ces

studie

dunder

field

and

gla

sshouse

conditio

ns.

Cd,Cu,Zn

Jun

cus

Phyto

extrac

tion,

Phyto

stab

iliz

atio

nPla

ntbio

accu

mula

tion

was

only

obse

rved

for

Cd,Cu,

and

Zn,bein

gsi

milar

for

Cd

atth

etw

osi

tes

and

signifi

-ca

ntly

hig

her

for

Cu

and

Zn,

nin

ean

dfo

ur

tim

es

hig

her,

resp

ect

ively

Est

uar

ine

environm

ent

[25]

Cr,

Pb,Zn,Cu

Spa

rtin

aa

lter

nifl

ora

,P

hra

gmit

esa

ust

rali

sM

eta

lupta

ke

Cu:300

mic

rog=g

inle

aves,

<200

mic

rog=g

inst

em

sZn:500

mic

rog=g

inse

di-

ments

,Cu:200

mic

rog=g

Meta

lco

nce

ntrat

ions

low

er

inst

em

sth

anin

leav

es,

and

Cr,

Pb,an

dZn

were

low

er

inP.

aust

ralis

than

inS.

alte

rnifl

ora

Meta

l-co

nta

min

ated

salt

mar

shes

study

[59]

Pb,Zn

Ph

ragm

ites

,Typ

ha

lati

fo-

lia,

Pa

spa

lum

dis

tich

um

Reduct

ion

inTSS

,Pb,

Zn,Cd,Cu

%99,98,75,83,an

d68%

reduc-

tion

inPb,Zn,Cd,Cu,an

dTSS

,re

spect

ively

Reduct

ion

rate

sofco

nta

mi-

nan

tsin

atreat

mentw

et-

land,So

uth

Chin

a

[18]

Cr

Typ

ha

lati

foli

a,

Ph

rag-

mit

esa

ust

rali

sAbio

tic

reduct

ion,pre

-ci

pitat

ion

and

accu

-m

ula

tion

ofCr

(III

)in

the

sedim

ents

Cr

(VI)

rem

oval

rate

sw

ere

0.0

05

to0.0

17

mg

L21

d2

1,

0.0

003–0.0

8m

gL2

1d

21,

and

0.0

04–0.1

3m

gL2

1d

21

for

the

control,

T.

lati

foli

a,

and

P.

au

stra

lis

mic

roco

sms,

resp

ect

ively

.

Gre

enhouse

and

bench

-sca

lem

icro

cosm

experim

ent

[21]

SeP

hra

gmit

es,

Typ

ha

Phyto

extrac

tion,

Phyto

stab

iliz

atio

n25–74mg

L21

reduct

ion

intreat

ed

wat

er

Est

ablish

ed

outd

oor

SSF

wetlan

d[6

0]

Cu,Cd,N

i,Pb,

Zn

Ph

ragm

ites

au

stra

lis

Adso

rption

After

thre

ecy

cles

of

adso

rption-e

lution,th

ead

sorp

tion

capac

ity

regai

ned

com

ple

tely

and

deso

rption

effi

ciency

of

meta

lar

ound

90%

Reed

bio

mas

suse

das

bio

-so

rbentfr

om

aqueous

solu

tion

[61]

Hg

Tra

nsg

enic

Spa

rtin

aa

lter

nifl

ora

Conve

rtin

gio

nic

Hg

into

ele

menta

ryH

gan

dvola

tiliza

tion

from

the

pla

nt

––

[15]

Mn,N

i,Cu,

Zn,Pb

Scir

pu

sli

ttora

lis

Meta

lupta

ke

by

pla

nt

Acc

um

ula

tion

ofM

n,N

i,Cu,

Zn,Pb

upto

494.9

2,56.3

7,

144.9

8,207.9

5,an

d93.0

8ppm

dry

wtin

90

day

stim

e

Meta

lac

cum

ula

tion

studie

dunder

wat

er-

logged

and

field

conditio

ns

for

90

day

s

[18]

Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep4 July 2013

Tab

le2.

Con

tin

ued

Meta

lVegeta

ted

pla

nts

Rem

oval

mech

an

ism

Rem

oval

stati

stic

sC

ase

stu

dy

Refe

ren

ces

Pb,M

n,Cr

Scir

pu

sa

mer

ica

nu

s,T

yph

ala

tifo

lia

Acc

um

ula

tion

inpla

nt

par

tsN

ear

ly100

%Rem

oval

ofPb,

Cr

and

71-1

00

%fo

rM

nduring

6-8

day

sof

experim

enta

tion

Acc

um

ula

tion

ofm

eta

lsby

invi

tro

rais

ed

pla

nts

insu

pple

-m

ente

dM

Sm

edia

[62]

Cu,Zn,Cd

Typ

ha

Act

ivity

ofth

ein

dig

e-

nous

soil

mic

roflora

and

pla

ntenzy

mes

–Const

ruct

ed

wetlan

d[6

3]

Cd,Cu,Zn,

Pb,Cr,

Ni,

Al,

Fe,M

n

Ph

ragm

ites

Acc

um

ula

tion

inpla

nt

par

ts12–62

mg

m-2

y-1

accu

mula

-tion

ofm

eta

lsin

VSS

Fin

leav

es

and

38–88

mg

m-2

y-

1in

stem

s23–56

mg

m-2

y-1

accu

mu-

lation

ofm

eta

lsin

HSS

Fin

leav

es

and

38–88

mg(m

22

yr2

1)

inst

em

s

Com

bin

ed

CW

inBelg

ium

treat

ing

dom

est

icw

aste

wat

er

[12]

Zn

Spa

rtin

ad

ensi

flora

Heav

ym

eta

lupta

ke

100–4800

ppm

Zn

Gla

sshouse

experim

ent

[64]

As,

Cu,Fe,M

n,

Pb,Zn

Spa

rtin

am

ari

tim

a,

Spa

rtin

ad

ensi

flora

Phyto

stab

iliz

atio

n,

Bio

accu

mula

tion

Zn

intiss

ues:

27

to1249

ppm

and

from

42

to2326

ppm

for

S.densi

flora

and

S.m

ari-

tim

aCu

intiss

ues:

22

to2546

ppm

and

from

27

to4933

ppm

for

S.densi

flora

and

S.m

aritim

aPb:0.1

to217

ppm

and

from

0.1

to292

ppm

for

S.densi

flora

and

S.m

aritim

e

To

study

meta

lac

cum

ula

tion

by

spar

tina

speci

es

intw

om

arsh

es

with

diffe

rentle

vels

ofpollution

[65]

Cd,Zn,Cr,

Cu,

Ni,

Pb

Ph

ragm

ites

Meta

lm

obility

and

upta

ke

Plu

mes:

19–117

lg

kg

21

DM

Cd,98–408

lgkg

21

DM

for

Cr,

3.1

–7.0

mg

kg

21

DM

for

Cu,0.5

–2.3

mg

kg

21

DM

for

Ni,

0.4

–4.5

mg

kg

21

DM

for

Pb,36–132

mg

kg

21

DM

for

Zn

Inte

rtid

alm

arsh

es

inth

eSc

held

test

uar

y[6

6]

Al,

Fe,M

nP

hra

gmit

esa

ust

rali

sM

eta

lac

cum

ula

tion

Root:

Al(O

H) 3>

Al 2O

3>

Fe

3O

4>

MnO

2>

FeO

OH

Heav

ym

eta

lsin

the

sedim

ent

ofco

nst

ruct

ed

wetlan

ds

[67]

Cd,Zn,Cr,

Cu,

Ni,

Pb

Ph

ragm

ites

au

stra

lis

Acc

um

ula

tion

inpla

nt

par

tsRhiz

om

es>

Stem

s>

Leav

es

Experim

enta

lco

nst

ruct

ed

wet-

land

(CW

)si

ted

inCas

tel-

novo

Bar

iano

[68]

Cu,Zn

Typ

ha

lati

foli

a,

Ph

rag-

mit

esa

ust

rali

sAcc

um

ula

tion

inpla

nt

par

tsCu,Zn:80

and

91%

for

unpla

nte

dco

ntrol,

83

and

92%

for

cattai

l,an

d83

and

92%

for

reed

wetlan

d

Riv

er

wat

er

conta

min

ated

by

swin

eco

nfined-h

ousi

ng

opera

tions

[69]

Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep July 2013 5

Tab

le2.

Con

tin

ued

Meta

lVegeta

ted

pla

nts

Rem

oval

mech

an

ism

Rem

oval

stati

stic

sC

ase

stu

dy

Refe

ren

ces

Al,

As,

B,Ba,

Cd,Co,Cr,

Cu,Fe,M

n,

Mo,N

i,Pb,

Se,Sn

,V,U

,Zn

Ph

ragm

ites

Acc

um

ula

tion

inpla

nt

par

tsRoots>

Rhiz

om

es>

Leav

es

>St

em

sConst

ruct

ed

wetlan

ds

with

horizo

nta

lsu

b-s

urf

ace

flow

(HF

CW

s)desi

gned

for

treat

mentofm

unic

ipal

sew

-ag

ein

the

Cze

chRepublic

[70]

Cd,Cr,

Cu,H

g,

Mn,N

i,Pb,

Zn

Ph

ragm

ites

Acc

um

ula

tion

inpla

nt

par

tsRootCd:1

.13

60.0

8,Cr:

6.9

76

0.1

9,Cu:1

4.9

86

0.9

3,

Hg:5.2

26

0.3

8,M

n:4

75.

80

611.9

1,N

i:9.1

26

0.2

0,

Pb:1

6.5

46

0.9

7,Zn

:104.1

06

9.2

8Rhiz

om

eCd:1

.00

60.0

8,Cr:1.5

26

0.0

6,Cu:4

.33

60.3

2,H

g:3

.19

60.2

6,

Mn:3

7.5

16

2.8

2,N

i:1.6

76

0.1

4,Pb:1

5.3

06

0.9

3,

Zn:3

2.6

76

2.3

6St

emCd:0

.68

60.0

6,Cr:0.4

06

0.0

4,Cu:2

.31

60.

28,

Hg:1

.05

60.

12,M

n:2

7.9

26

2.3

4,N

i:0.4

86

0.0

8,Pb:

9.8

76

0.8

0,Zn:1

0.04

60.8

7Le

afCd:1

.05

60.1

0,Cr:0.

696

0.04

,Cu:4

.13

60.1

9,H

g:1

.73

60.2

3,M

n:3

08.3

06

11.

47,N

i:1.6

96

0.1

5,Pb:1

3.2

06

0.7

4,Zn:2

8.40

61.7

2

Phra

gm

ites

aust

ralis

and

the

corr

esp

ondin

gw

ater,

sedi-

mentsa

mple

sfr

om

the

mouth

area

ofth

eIm

era

Meridio

nal

eRiv

er

(Sic

ily,

Ital

y)

[71]

Pb,Cu,Zn

Ph

ragm

ites

––

–[7

2]

Zn

Ph

ragm

ites

au

stra

lis,

Aco

rns

cala

mu

s,Sc

ir-

pu

sta

ber

na

emon

tan

i

Acc

um

ula

tion

inpla

nt

par

tsSc

irpus

tabern

aem

onta

ni:

Rem

oval

effect

sw

ere

31,0

50.8

4m

g=kg

(10,2

06.6

7m

g=kg

inab

ove-g

round

par

tsan

d20,8

44.

17

mg=kg

inunder-

gro

und

par

ts)

Aco

-ru

sca

lam

us

and

Phra

gm

ites

aust

ralis,

the

hig

hest

accu

-m

ula

tion

conce

ntrat

ions

of

zinc

ion

were

54,1

30.6

7m

g=kg

(16,7

74.0

0m

g=kg

inab

ove-g

round

par

tsan

d37,3

56.6

7m

g=kg

inunder-

gro

und

par

ts)

and

25,4

23.3

4m

g=kg

(4506.6

7m

g=kg

inab

ove-g

round

par

tsan

d20,9

16.6

7m

g=kg

inunder-

gro

und

par

ts)

Hydro

ponic

ally

culture

d[7

3]

Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep6 July 2013

Tab

le2.

Con

tin

ued

Meta

lVegeta

ted

pla

nts

Rem

oval

mech

an

ism

Rem

oval

stati

stic

sC

ase

stu

dy

Refe

ren

ces

Cu,Zn,Cd,Pb

Ph

ragm

ites

au

stra

lis

Phyto

extrac

tion

Cu,Zn,Cd:so

il>

Phra

gm

ites

aust

ralis

ofae

rial

par

t>-

phra

gm

ites

aust

ralis

of

underg

round

par

tPb:So

il>

Phra

gm

ites

aust

ralis

ofae

rial

par

t�phra

gm

ites

aust

ralis

of

underg

round

par

t

Riv

er

wetlan

dsy

stem

[74]

Cd,Cr,

Cu,Fe,

Ni,

Pb

Ph

ragm

ites

cum

mu

nis

,T

yph

aa

ngu

stif

oli

a,

Cyp

eru

ses

cule

ntu

s

Acc

um

ula

tion

inpla

nt

par

tsP.

cum

munis

was

inth

eord

er

ofFe

(2813)>

Mn

(814.4

0)

>Zn

(265.8

0)>

Pb

(92.8

0)

>Cr

(75.7

5)>

Cu

(61.7

7)

>N

i(4

5.6

9)>

Cd

(4.6

9)

T.

angust

ifolia:

Fe>

Mn>

Zn

>Cr>

Pb>

Cu>

Ni>

Cd

C.esc

ule

ntu

s:Fe>

Mn>

Zn

>Pb>

Ni>

Cu>

Cr>

Cd

Pla

nts

gro

wn

inaq

ueous

solu

tion

[75]

Cr,

Cu,Pb,Fe,

Zn

Spa

rtin

aa

lter

nifl

ora

Phyto

extrac

tion

Cr:

3.0

ppm

,Cu:7.0

ppm

,Fe:

410

ppm

,Pb:0.5

ppm

,Zn:2

8ppm

indry

soil

Sedim

ents

invar

ious

loca

tions

inBay

ou

d’Inde

inSo

uth

-w

est

Louis

iana

aw

aterw

ay(indust

rial

and

munic

ipal

was

test

ream

s)

[76]

Cd

Typ

ha

an

gust

ifoli

aH

ypera

ccum

ula

tion

inpla

nts

Cd

conc

inRoot-

1962.3

16

32.7

0m

gL2

1Cd

conc

inLe

af2

39.6

66

1.7

6m

gL2

1

Lab

scal

egre

en-h

ouse

study

[77]

Al,

Fe,Zn,Pb

Typ

ha

dom

inge

nsi

sRhiz

ofiltra

tion

Pb21

>Fe31>

Al31>

Zn21

Rai

sing

pla

nts

hydro

ponic

ally

and

tran

spla

nting

them

into

meta

l-pollute

dw

aters

[78]

As,

Cd,Pb

Typ

ha

ori

enta

lis

Tole

rance

Acc

um

ula

tion

–G

reenhouse

study

[79]

Cr,

Cd,Pb

Typ

ha

an

gust

ifoli

aH

eav

ym

eta

lupta

ke

–Potexperim

ent

[80]

Co,Cr,

Ni

Spa

rtin

aPhyto

stab

iliz

atio

nBio

accu

mula

tion

Co

intiss

ues:

B0.1

–35.8

and

from

B0.1

–43.4

lgg

21

for

S.densi

flora

and

S.m

aritim

aCr

intiss

ues:

2–18.8

and

from

B0.1

–25.2

lgg-1

for

S.densi

flora

and

S.m

aritim

aTis

sue

Ni:

B0.5

–11.1

and

from

B0.5

–15.6

lgg-1

for

S.densi

flora

and

S.m

aritim

e

Meta

lco

nta

min

ated

site

study

[81]

Cr,

Ni,

Zn

Typ

ha

dom

inge

nsi

sH

eav

ym

eta

lupta

ke

BFs:

Cr

0.1

81,N

i0.2

47,Zn

0.8

57

TFs:

Cr

0.1

52,N

i0.0

30,Zn

0.1

97

Prim

ary

treat

mentw

etlan

d(w

aste

wat

er

from

indust

rial

pro

cess

es

and

sew

age

from

the

fact

ory

)

[82]

Hg

Jun

cus

ma

riti

mu

s,Sc

ir-

pu

sm

ari

tim

us

Phyto

stab

iliz

atio

nPhyto

accu

mula

tion

–H

g-c

onta

min

ated

salt

mar

shse

dim

entch

em

ical

environm

ent

[83]

Cr

Spa

rtin

aa

rgen

tin

ensi

sH

ypera

ccum

ula

tion

–G

lass

house

experim

ent

[84]

Zn,Cd,Cu

Ph

ragm

ites

au

stra

lis

Meta

lac

cum

ula

tion

–[8

5]

Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep July 2013 7

Combinations of the various phytoremediation processesmay occur simultaneously or in sequence for a particularcontaminant, or different processes may act on different. Theidentifying characteristics associated with wastewater arehigh BOD and COD value, suspended and dissolved solids,heavy metals and xenobiotics. Biological characteristicsinclude coliforms, and other types of bacteria. When suchwater was subjected to a standardized retention time in aconstructed wetland, the pollutant=contaminant load comesdown to allowable limits to be discharged into environment.For fecal coliforms one log to two log reductions have beenachieved. Removal of nitrogen in the form of ammonia andorganic nitrogen requires a supply of oxygen for nitrification,which comes from plant roots that don’t penetrate com-pletely. The reduction obtained in BOD is 85.71%, COD86.14%, TSS 87.58%, TS 87.64%, total N 81.55% along grow-ing in constructed wetland for distillery effluent [90].Removal of heavy metals occurs mainly by binding to soils,sediments and particulate matter or precipitation as insolublesalts and uptake by bacteria, algae and plants. The majorproportion of heavy metal removal is accounted for by bind-ing processes within wetlands [91]. Because of their positivecharge, the heavy metals are readily adsorbed, complexedand bound with suspended particles, which subsequentlysettle on the substrate. The precipitation of heavy metals asinsoluble salts such as carbonates, bicarbonates, sulfides andhydroxides is another process that leads to their long termremoval. These salts are formed as a result of reactionbetween heavy metals with other chemicals and lead to pre-cipitation and settling of metal salts [92]. Some wetland plantspecies have been found to have a property of heavy metaltolerance, for example, Typha latifolia, Glyceria fluitans andPhragmites australis. Tables (2–4) depicts the capacity ofremediation potential of different macrophytes to variouscontaminants.

From the review of literature as compiled in above tables,an inference can be easily made about the trend of differentmetals being remediated by wetland plants. Major metals tobe remediated in constructed wetlands are Pb [7,26,70], Zn[7,71], Cd [7,26,70]), Cu [71], Cr [71].These metals can betermed as most common heavy metal pollutant present inwastewater=soil followed by Al > As > B > Ba > Co > Fe> Hg > Mn > Ni > P, Mo > N > As > Se > Sn > U > V.

The presence of these metals can be attributed to dis-charge of industrial, gases, effluents and solid waste into theenvironment. The above case studies have been done in labscale, pilot scale, glass house or hydroponically grown cul-tures later treated with metal spiked water. Most of the litera-ture cited over time explains the data on metalaccumulations in various plant parts (root, stem, leaves) andin soil=sediments. So far there has been no focus on technol-ogy mechanisms= microbe’s role=enzymatic processesinvolved in the remediation processes. The comparativeanalysis of remediation of different types of wastewater (ascompiled in Tables (1–4)) reveals that Phragmites are mostcommonly used plant species. Around 41% of of CWs arevegetated with Phragmites solely or in combination withother plant, for example, Acorns calamus, Scirpus tabernae-montani [73], Typha latifolia [69], Cyperus esculentus [25],Spartina alterniflora [59]. Typha (23%), Spartina (15%), Scir-pus (8%) and Juncus (5%) are other important plants afterPhragmites. Plants less used include Cyperus, Acorns, Lemna,Paspalam. For the treatment of xenobiotics, Phragmites aremajorly used plants (32%), followed by Typha (22%), Juncus(11%). Other species less used are Medicago, Glyceria, Pha-laris, Oryza, Carex, Sparganium, Poa, Scirpus, and Spartina.Major remediation processes are accumulation, degradation,mineralization and metabolism due to microbial activities.Xenobiotics largely include pesticides Fenpropimorph,Linuron, Metalaxyl, Metamitron, Metribuzin, Propachlor,Ta

ble

2.

Con

tin

ued

Meta

lVegeta

ted

pla

nts

Rem

oval

mech

an

ism

Rem

oval

stati

stic

sC

ase

stu

dy

Refe

ren

ces

Acc

um

ula

tion

inre

eds

(Phra

g-

mites

aust

ralis)

inurb

anse

dim

ents

from

two

storm

-w

ater

infiltra

tion

bas

ins

Cu,Zn,Cd,Pb

Ph

ragm

ites

kark

aM

eta

lto

lera

nce

,U

pta

ke,A

ccum

ula

tion

Cu>

Zn>

Cd>

Pb

–[8

6]

Al,

Pb,Cd,Co,

Ni,

Cr,

Fe,

Mn,Zn,Cu

Ph

ragm

ites

au

stra

lis

Meta

lac

cum

ula

tion

Al>

Pb>

Cd>

Co>

Ni>

Cr

mic

ronutrie

nts

:Fe>

Mn

>Zn>

Cu

Phra

gm

ites

aust

ralis

gro

win

gat

4se

lect

ed

site

sal

ong

the

ban

kofth

elo

wer

Riv

er

[87]

Cd

Jun

cus

subse

cun

du

sM

eta

lac

cum

ula

tion

Cad

miu

mac

cum

ula

tion

and

rem

oval

(exce

ptfo

rCd

rem

oval

at20

mg

Cd

kg

21)

by

pla

nts

was

signifi

cantly

hig

her

inCd

treat

ments

with

than

withoutPA

H

Gla

sshouse

experim

entw

asco

nduct

ed

toin

vest

igat

eeffect

sofCd)

without

orw

ith

PAH

son

gro

wth

of

Juncu

ssu

bse

cundus

[88]

Hg

Ph

ragm

ites

au

stra

lis

Acc

um

ula

tion

inpla

nt

par

tsRoot(0

.321

60.0

5BCD

)exhib

ited

the

hig

hest

Hg

accu

mula

tion

follow

ed

by

rhiz

om

e(0

.245

60.0

4BCD

)an

dle

aves

Hg-c

onta

min

ated

coas

tal

lagoon

[89]

Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep8 July 2013

Tab

le3.Rem

edia

tion

pote

ntial

ofdiffe

rentw

aste

wat

er

usi

ng

wetlan

dpla

nts

Typ

eo

fw

ast

ew

ate

rVegeta

ted

pla

nts

Rem

oval

Mech

an

ism

Rem

oval

Sta

tist

ics

Case

stu

dy

Refe

ren

ces

Indust

rial

was

tew

ater

Ph

ragm

ites

,Sc

hoen

ople

ctu

s,C

yper

us,

Typ

ha

Upta

ke

by

pla

nts

50%

ofin

fluentm

eta

llo

adConst

ruct

ed

wetlan

ds

[16]

Min

era

liza

tion

and

pat

hogen

conta

inin

gw

aste

wat

er

Ph

ragm

ites

Tre

atm

entin

wetlan

dby

adso

rption

tobio

film

sTw

oto

thre

elo

gcy

cle

reduct

ion

inco

unts

of

indic

ator

bac

teria

Fie

ldsc

ale

gra

velbed

hydro

ponic

sco

n-

stru

cted

wetlan

d

[93]

Min

eeffl

uent

Typ

ha

Acc

um

ula

tion

intiss

ues,

pre

cipitat

ion

asiron-

hydro

xid

es

inro

ot

zones

0–99%

and

0–64%

reduct

ion

for

Zn

and

Pb

inpond

1an

d94–

99%

for

Zn

and

25–

60%

for

Pb

inpond

2,

69%

rem

oval

rate

sof

sulp

hat

ein

eac

hpond

Series

ofsu

bsu

rfac

eflow

ponds

filled

with

spentm

ush

room

sub-

stra

teco

nst

ruct

ed

atN

avan

,Ir

ela

nd

[56]

Dai

ryw

aste

wat

er

Ph

ragm

ites

au

stra

lis,

Scir

pu

sva

lid

us

Tre

atm

entby

wetlan

dpla

nts

and

resi

din

gbac

teria

Rem

oval

rate

:TK

N25%

,am

moniu

mle

vel16%

,BO

D73%

,SS

91%

,CO

D38%

,Fae

calco

li-

form

s99%

CW

for

dai

ryw

aste

wat

er

[94]

Nitro

gen

and

Bac

terial

conta

min

ated

wat

er

Ph

ragm

ites

,T

yph

aPla

ntam

monia

assi

mila-

tion,nitrifica

tion,re

s-titu

tion

ofst

ore

dnitro

gen

inth

evege-

taltiss

ues

Rem

oval

rate

:27%

inK

jeld

ahlN

itro

gen,

19%

amm

onia

nitro

-gen,4%

nitra

te-n

itrite

,90%

for

bac

teria

Tw

ow

etlan

dco

mbin

ed

syst

em

-one

vertic

alan

doth

er

horizo

nta

l

[95]

Textile

effl

uent

Ph

ragm

ites

Min

era

liza

tion

and

degra

dat

ion

70%

rem

ova

leffi

cacy

Degra

dat

ion

inVFCW

[96]

Dilute

farm

effl

uent,

dirty

wat

er

Ph

ragm

ites

Bio

logic

altreat

mentof

was

tew

ater

inac

ti-

vat

ed

sludge

and

wet-

land

conditio

ns

Reduct

ion

inpH

val

ue

from

10.9

to7.6

,BO

D821

to65

mg=L,

CO

D2005

to210

mg=L,

and

amm

oniu

m0.3

to<

0.1

for

eac

hw

etlan

dbed

Aera

ted

sequenci

ng

bat

chre

acto

rco

nta

in-

ing

activat

ed

sludge

follow

ed

by

ase

ries

ofco

nst

ruct

ed

wetlan

ds

[97]

Rem

oval

ofbac

teria

insa

nd

colu

mns

Jun

cus

effu

ses,

Ph

ragm

ites

au

stra

lis

Pre

dat

ion

and

lysi

sEffi

ciency

ofre

moval

upto

four

ord

ers

of

mag

nitude

ofcf

uobta

ined

Rem

ova

lofbac

teria

inpla

nte

dan

dunpla

nte

dsa

nd

colu

mns

[98]

Dom

est

icw

aste

wat

er

Ph

ragm

ites

Sedim

entac

cum

ula

tion

Conce

ntrat

ions

ofCd,

Cu,Pb,an

dZn

inth

ese

dim

entgenera

lly

decr

eas

ed

along

the

treat

mentpat

hofth

eCW

Com

bin

ed

CW

:tw

oVSS

Fre

ed

beds

fol-

low

ed

by

two

HSS

Fre

ed

beds

[12]

Urb

anru

noff

Ph

ragm

ites

Tre

atm

entin

wetlan

dRem

oval

perf

orm

ance

ofpla

nte

dfilters

was

more

effi

cien

tan

dst

a-ble

afte

rth

efilters

mat

ure

dco

mpar

ed

toth

atofunpla

nte

dfilters

Experim

enta

lte

mpora

r-ily

flooded

vertic

al-

flow

wetlan

dfilters

treat

ing

urb

anru

noff

[99]

Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep July 2013 9

Tab

le3.

Con

tin

ued

Typ

eo

fw

ast

ew

ate

rV

egeta

ted

pla

nts

Rem

oval

Mech

an

ism

Rem

oval

Sta

tist

ics

Case

stu

dy

Refe

ren

ces

Nitra

te-d

om

inan

tw

aste

wat

er

Typ

ha,

Scir

pu

sEnhan

ced

bio

logic

aldenitrifica

tion

by

fuel-

ing

hete

rotrophic

mic

robia

lac

tivity

Nitra

tere

moval

were

around

500

mgN=(m

2

d).

Are

alre

moval

rate

25%

hig

her

inca

ttai

lvers

us

bulrush

meso

-co

sms.

DO

inbulrush

betw

een

0.5

and

2m

gL2

1,w

hile

DO

inca

t-ta

ilm

eso

cosm

sbelo

w0.3

mg

L21

Bat

chw

etlan

dm

eso

cosm

s[1

00]

Indust

rial

was

tew

ater

Typ

ha

lati

foli

a,

Ph

ragm

ites

au

stra

lis

Upta

ke

by

pla

nts

and

reedbed

aera

tion

Hig

hre

moval

oforg

an-

ics

from

tannery

was

tew

ater,

up

to88%

ofBO

D5

(fro

man

inle

tof420–1000

mg

L21)

and

92%

of

CO

D(f

rom

anin

letof

808–2449

mg

L21)

Tw

o-s

tage

const

ruct

ed

wetlan

ds

pla

nte

dw

ith

Typha

latifo

lia

and

Phra

gm

ites

aust

ralis

[101]

Hig

h-s

trength

was

tew

ater

Typ

ha

an

gust

ifoli

a,

Cyp

eru

sin

volu

cra

tus

Aera

tion

by

pla

ntro

ots

Avera

ge

mas

sre

moval

rate

sofCO

D,TK

Nan

dto

tal-P

ata

HLR

of80

mm

d2

1w

ere

17.8

,15.4

,an

d0.6

9gm

22

d2

1

Vertic

alflow

(VF)

con-

stru

cted

wetlan

dsy

s-te

ms

totreat

hig

h-

stre

ngth

was

tew

ater

under

tropic

alcl

imat

icco

nditio

ns

[102]

Sludge

stab

iliz

atio

nP

hra

gmit

esReedbeds

aera

tion

–Reed

bed

pilotpla

ntfo

rsl

udge

stab

iliz

atio

n[1

03]

Dom

est

icw

aste

wat

er

Ph

ragm

ites

au

stra

lis,

Ph

ala

ris

aru

nd

ina

cea

Aera

tion

by

pla

ntro

ots

NH

4-N

conce

ntrat

ion

of

29.9

mg=L

was

reduce

dto

6.5

mg=L

avera

ge

rem

ova

leffi

-ci

ency

of78.3

%.

Rem

oval

ofBO

D5

and

CO

Dam

ounte

dto

94.5

and

84.4

%Phosp

horu

sre

moval

amounte

dto

65.4

%

Thre

e-s

tage

experim

en-

talco

nst

ruct

ed

wetlan

d

[104]

Dom

est

icw

aste

wat

er

Ph

ragm

ites

au

stra

lis

Deco

nta

min

atio

neffect

ofPhra

gm

ites

aust

ralis

Deco

nta

min

atio

nra

te:

64.5

%fo

rBO

D,68%

for

CO

D,79.7

%fo

rSS

,21.0

%fo

rTota

lPhosp

horu

s,20.7

%fo

rto

talnitro

gen

Pilotsu

bsu

rfac

ehori-

zonta

lflow

con-

stru

cted

wetlan

d

[105]

Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep10 July 2013

Propiconazole), PAHs [Benzene, Toluene, Ethylbenzene,Xylenes (BTEX) and dyes (Textile azo dye, acid orange 7)].Along with degradation, some of these are also retainedwithin soil=sediments along the length of wetland [71,114].

Being eco-friendly, Phragmites (Reeds) constructed wet-land is often termed as “Ecoflo reed bed system.” It hasmany advantages over the other water treatment technolo-gies for primary, secondary or tertiary wastewater treatmentin private housing=communal=commercial developmentsbecause of easy integration in new and existing housingschemes. Being a living system, reed beds work in harmonywith the environment blending visually with the natural land-scape which is particularly important in scenic areas [32,119].These are extremely durable and provide a reliable, long-term solution to wastewater=sewage treatment as per theireffectiveness in preventing faecal contamination from reach-ing wells, reservoirs and surface waters is concerned. A well-constructed wetland can effectively remove all suspendedsolids from wastewater. Moreover reed beds require low-maintenance as its maturation with time essentially looksafter itself. These systems are very competitively valuedwhen compared to other treatment systems because unlikeconventional systems, these improve with age as the rootsmature and expand with time becoming more efficient forbiologically filtering wastewater. After the plants have beenallowed to grow for some time, they are harvested from thewetlands and incinerated [27]. This procedure is practiced tillthe contaminant level in water comes down to allowablelimit. Constructed either with horizontal or vertical flow thesewetlands act as a mechanism to treat non-point source pollu-tion before it reaches lakes, rivers and oceans. Experimentscarried out with planted and unplanted reedbeds on samesubstrate have shown a significant influence on nutrientremoval [34,120]. Moreover, the aquatic vegetation in wet-lands plays an important role in removing nutrients [36–38,121–123]. Plants take up nutrients primarily through theirroot systems, only some uptake occurs through immersedstems and leaves from the surrounding water. Aerial stem byvirtue of large internal air spaces transport oxygen to theroot area of the soil to enable aerobic microbes to decom-pose the pollutant [124] and aid in the settling of suspendedmaterial by reducing the rate of sewage flow [125].

FUTURE PROSPECTS AND NEW TRENDS

Increasing the efficiency of system and bringing theexperimental results at par with the field activities has alwaysbeen a big challenge to all environment engineers and scien-tists. To increase the efficiency of constructed wetlands, thereis a need for better knowledge of the biological processesinvolved in plant-microbe-contaminant interactions, novelgenes for bioremediation in plant and bacteria, molecularand biochemical approaches in the degradation pathwaysand whole mobile genetic pool (consisting of plant and rhi-zospheric bacteria) in a constructed wetland. Introducingcertain novel amendments can meet the high standard of rec-lamation in a given environmental matrix. Apart from thebiological processes, an understanding of physical and chem-ical processes occurring in the system also offers a great helpin understanding the system and increasing its efficiencymanifolds. Amendments can be in terms of planting two ormore species, for example, planting Sparganium erectum,Phragmites australis, Phalaris arundinacea, Glyceria flui-tans, Typha latifolia together in a wetland. Such a combina-tion has been used in retention of pesticides likeFenpropimorph, Linuron, Metalaxyl, Metamitron, Metribuzin,Propachlor, Propiconazole in soils [14]. Using two or moreplant species together in a wetland adds to scenic beautyand also increases efficiency of wetland as there may bemore than one organic pollutant specific to different plantsfor accumulation and remediation purpose.Ta

ble

3.

Con

tin

ued

Typ

eo

fw

ast

ew

ate

rVegeta

ted

pla

nts

Rem

oval

Mech

an

ism

Rem

oval

Sta

tist

ics

Case

stu

dy

Refe

ren

ces

Nutrie

ntre

moval

Ph

ragm

ites

ma

uri

tia

nu

sRem

edia

tion

by

pla

nts

Conduct

ivity

val

ues

decr

eas

ed

by

24

and

28%

inw

etlan

d1

and

wetlan

d2,TD

Sdecr

eas

ed

by

32%

and

28%

,Am

moniu

mnitro

gen

incr

eas

ed

by

5%

inw

etlan

d1

and

12%

inw

etlan

d2,

nitra

tenitro

gen

decr

eas

ed

by

62

and

56%

,Reac

tive

phos-

phoru

sco

nce

ntrat

ions

were

reduce

dby

4an

d3%

,in

wetlan

d1

and

wetlan

d2

Horizo

nta

lSu

bsu

rfac

eFlo

wConst

ruct

ed

Wetlan

ds

[106]

Munic

ipal

was

tew

ater

Ca

nn

a,

Ph

ragm

ites

,C

ypru

sRem

edia

tion

by

pla

nts

Rem

oval

effi

cien

cy:

CO

D88%

,BO

D90%

,TSS

92%

Vertic

alflow

const

ruct

ed

wetlan

ds

[107]

Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep July 2013 11

Tab

le4.Rem

edia

tion

pote

ntial

ofXenobio

tics

invar

ious

wetlan

dpla

nts

Xen

ob

ioti

cs

Vegeta

ted

pla

nts

Rem

oval

mech

an

ism

Rem

oval

Sta

tist

ics

Case

stu

dy

Refe

ren

ces

Gly

col-bas

ed

deic

ing

agent

Scir

pu

ssp

p.,

Med

ica

gosa

tiva

,P

oa

pra

ten

sis

Degra

dat

ion

60.4

,49.6

,an

d24.4

%of

applied

[14C]E

Gdegra

ded

to14CO

2in

the

Med

ica

gosa

tiva

,P

oa

pra

ten

sis,

and

nonvegeta

ted

soils,

Scir

pu

ssp

p.enhan

ced

the

min

era

li-

zation

of[1

4C]P

Gby

11–

19%

and

[14C]E

Gby

6–20%

.

Vegeta

ted

wat

er

incu

bat

ion

syst

em

s[9

]

Atraz

ine

Ph

ragm

ites

Rete

ntion

inw

etlan

dBetw

een

17–4

2%

ofm

eas

ure

dat

razi

ne

mas

sw

asobta

ined

within

30–36

mofw

etlan

d

Am

endm

entofat

razi

ne

ina

const

ruct

ed

wetlan

d[5

2]

Meta

laxylan

dSi

maz

ine

(hydro

carb

ons)

Typ

ha

Acc

um

ula

tion

inpla

ntpar

tsM

eta

laxylan

dsi

maz

ine

activ-

ity

inso

lution

was

reduce

d34

and

65%

–[1

08]

PAH

-degra

dat

ion

Ph

ragm

ites

Degra

dat

ion

––

[54]

Cru

de

oil

Typ

ha

lati

foli

a,

Typ

ha

an

gust

ifoli

a,

Ph

rag-

mit

esco

mm

un

is,

Scir

-pu

sla

cust

ris,

Jun

cus

spp.

Degra

dat

ion,m

icro

bia

ldis

sim

-ilat

ory

sulp

hat

ere

duct

ion

and

bio

sorp

tion

Oil

conte

ntofth

ew

ater

afte

rtreat

mentw

asdecr

eas

ed

tole

ssth

an0.2

mg=L

from

2–

10

mg=L,

and

the

conce

ntra-

tions

ofheav

ym

eta

lsdecr

eas

ed

belo

wth

ere

le-

van

tperm

issi

ble

levels

Pas

sive

syst

em

ofth

ety

pe

of

the

const

ruct

ed

wetlan

ds

[109]

2,6

-dim

eth

ylp

henol,

4-

chlo

rophenol,

Nap

hth

alene

Ca

rex

gra

cili

s,Ju

ncu

sef

fusu

sD

egra

dat

ion

Conce

ntrat

ions

of20

mg=L

org

anic

polluta

ntin

the

case

of4-c

hlo

rophenol,

about30

mg=L

nap

hth

alene

and

50

mg=L

2,6

-dim

eth

ylp

henol

were

effi

ciently

elim

inat

ed

Hydro

ponic

culture

susi

ng

sand-b

ed

reac

tors

pla

nte

dunder

bat

chan

dflow

-th

rough

conditio

ns

[41]

Oil

Spill

Spa

rtin

aD

egra

dat

ion

and

accu

mula

tion

–Const

ruct

ed

wetlan

ds

[110]

Benze

ne,Tolu

ene,Eth

-ylb

enze

ne,Xyle

nes

(BTEX)

Scri

pu

scy

per

inu

s,Ju

n-

cus

effu

ses,

Ca

rex

luri

da,

Typ

ha

lati

foli

a

Phyto

degra

dat

ion,

Phyto

vola

tiliza

tion

90

%ofth

eBTEX

rem

oved

Const

ruct

ed

wetlan

ds

[53]

Fenpro

pim

orp

h,

Linuro

n,M

eta

laxyl,

Meta

mitro

n,M

etrib

u-

zin,Pro

pac

hlo

r,Pro

pic

onaz

ole

Spa

rga

niu

mer

ectu

m,

Ph

ragm

ites

au

stra

lis,

Ph

ala

ris

aru

nd

ina

-ce

a,

Gly

ceri

afl

uit

an

s,T

yph

ala

tifo

lia

Rete

ntion

ofpest

icid

es

inar

a-ble

soils

3–67%

rete

ntion

ofpest

icid

es

(Fenpro

pim

orp

h,Li

nuro

n,

Meta

laxyl,

Meta

mitro

n,M

et-

ribuzi

n,Pro

pac

hlo

r,Pro

pic

onaz

ole

)

Const

ruct

ed

wetlan

ds

[71]

Azo

dyes

Ph

ragm

ites

Min

era

liza

tion

and

degra

dat

ion

Near

ly70%

rem

oval

effi

cacy

Degra

dat

ion

inVFCW

[96]

DD

T,PCBs

Ph

ragm

ites

au

stra

lis,

Ory

za

sati

vaAcc

um

ula

tion

inpla

ntpar

tsan

dtran

sform

atio

nby

reduct

ive

hal

ogenat

ion

92.0

–95.0

ng

DD

Tin

roots

and

70.5

–78.0

ng

inst

em

of

reeds

Gla

sshouse

experim

ents

under

hydro

ponic

conditio

ns

[71]

Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep12 July 2013

Tab

le4.

Con

tin

ued

Xen

ob

ioti

cs

Vegeta

ted

pla

nts

Rem

oval

mech

an

ism

Rem

oval

Sta

tist

ics

Case

stu

dy

Refe

ren

ces

Org

anic

polluta

nt

Ph

ragm

ites

Bio

degra

dat

ion

and

pla

nt

upta

ke

>90%

rem

oval

ofLi

ndan

e,

Penta

chlo

rophenol,

Endo-

sulp

han

and

Penta

chlo

ro-

benze

ne;80–90%

for

Ala

chlo

ran

dChlo

rpyriphos;

20%

for

Meco

pro

pan

dSi

maz

ine

HSS

Fpilotpla

ntin

Spai

n[1

11]

Textile

azo

dye

acid

ora

nge

7P

hra

gmit

esa

ust

rali

sD

egra

dat

ion

by

pla

nt

–VFCW

treat

ment

[112]

Bis

phenolA,Bis

phenol

FP

hra

gmit

esa

ust

rali

sBio

degra

dat

ion

by

rhiz

osp

here

bac

teria

–BPA

and

BPF

degra

dat

ion

inth

ese

dim

ent

[113]

Ibupro

fen,Car

bam

aze-

pin

e,Clo

fibric

acid

Typ

ha

Adso

rption

on

LECA

and

phyto

degra

dat

ion

Rem

oval

effi

cienci

es

of96,97,

and

75%

for

ibupro

fen,ca

r-bam

azepin

ean

dcl

ofibric

acid

insu

mm

er,

26%

inre

moval

effi

ciency

was

obse

rved

for

clofibric

acid

inw

inte

r

Mic

roco

smco

nst

ruct

ed

wet-

lands

syst

em

sest

ablish

ed

with

am

atrix

oflight

expan

ded

clay

aggre

gat

es

(LECA)

and

pla

nte

dw

ith

Typha

[114]

Car

bam

azepin

eT

yph

aU

pta

ke

and

meta

boliza

tion

CB

rem

ova

l:56%

for

the

CB

initia

lco

nce

ntrat

ion

of2.0

mg

L21

1to

82%

Hydro

ponic

conditio

ns

[114]

Eenro

floxac

in(E

NR),

Ceftio

fur

(CEF),

Tetra-

cycl

ine

(TET)

Ph

ragm

ites

au

stra

lis

Acc

um

ula

tion

inpla

ntpar

tsLe

vels

of6

62

lgL2

1fo

rSW

Pan

d43

65

lgL2

1fo

rco

ntrolsa

mple

saf

ter

7day

-s,

resu

ltin

gin

94

and

57%

of

dru

gre

moval

Was

tew

ater

treat

mentpla

nts

(WW

TPs)

[115]

PAH

Jun

cus

subse

cun

du

sPA

Hdegra

dat

ion

Cad

miu

mac

cum

ula

tion

and

rem

oval

(exce

ptfo

rCd

rem

oval

at20

mg

Cd

kg

21)

by

pla

nts

was

signifi

cantly

hig

her

inCd

treat

ments

with

than

withoutPA

Hs,

where

asac

cum

ula

tion

ofPA

Hs

by

pla

nts

(exce

ptfo

rpyre

ne

inro

ots

at0

added

Cd)

Gla

sshouse

experim

ent

[88]

Terb

uth

yla

zine

(TER)

Typ

ha

lati

foli

aD

egra

dat

ion

by

pla

nt

–D

egra

dat

ion

pat

hw

ays

ofte

r-buth

yla

zine

(TER)

by

Typha

latifo

lia

inco

nst

ruct

ed

wetlan

ds

[116]

4C-lab

ele

d1,4

-dic

hlo

ro-

benze

ne

(DCB),

1,2

,4-

tric

hlo

robenze

ne

(TCB),

g-

hexac

hlo

rocy

clohexan

e(g

HCH

)P

hra

gmit

esPla

ntupta

ke

Pla

ntupta

ke

of

DCB,TCB,

gH

CH

was

signifi

cant

with

bio

con-

centrat

ion

fact

ors

reac

hin

g14,

19,an

d15

Hydro

ponic

conditio

ns

[117]

Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep July 2013 13

The primary filtering and aeration of wastewater can bedone so that there is a pre settlement of suspended particu-late matter prior to releasing it into Phragmites root zone.The aeration pumps can be applied at site of collectiontanks and aeration can be provided at different levels in thetank with the help of spurges or nozzles. The aeration canbe done for 20–30 h to make the environment partially aer-obic and to increase the level of dissolved oxygen in thewastewater. Pre-settlement tank and aeration chambers canbe provided in vicinity of constructed wetlands which cansupport for primary treatment of water. Use of soil amend-ments such as synthetics (ammonium thiocyanate) and nat-ural zeolites have yielded promising results [126–130].EDTA, NTA, citrate, oxalate, malate, succinate, tartrate,phthalate, salicylate and acetate etc. have been used as che-lators for rapid mobility and uptake of metals from contami-nated soils by plants. Use of synthetic chelators significantlyincreased Pb and Cd uptake and translocation from roots toshoots facilitating phytoextraction of the metals from lowgrade ores [27].

Adding certain microbial components along with theseplants which degrades various pollutants and contaminantscan be a rationalized approach for treating wastewater witha variety of pollutants. The rhizosphere of wetland plantcan be considered as elevated zone in terms of microbialpresence and activity. Adding certain inoculants, not nativeand having higher remediation potential generates a biasedrhizosphere termed as Designer Rhizospheres [131]. Bioaug-mentation, the addition of microbes to enhance a specificbiological activity, has been practiced intentionally for yearsin wastewater treatment [132]. In the constructed wetlands,the role of rhizospheric microbial population is quite activerelative to passive role of vegetation. Certain bacteria hav-ing the ability to degrade a particular pollutant=contaminantbased on their natural, non-engineered metabolic processescan be employed for the remediation purpose [133]. Thisuse of rhizomicrobial populations present in the rhizo-sphere of plant for bioremediation is termed as rhizoreme-diation [48] and when microbial populations are addedfrom outside source, then it is known as bioaugmented rhi-zoremediation [48,134–136]. In most of cases, bioaugmenta-tion impact on indigenous microbes is often overlookedkeeping remediation as primary goal. Addition of microbesto soil can potentially result in establishment of new micro-bial population, shifts in microbial population or transfer ofgenetic material (like plasmids harboring metal=antibioticresistance genes) to indigenous population which is not itsprimary goal [131].

The intentional stimulation of resident xenobiotic degrad-ing bacteria by addition of electron acceptors, water,nutrients or electron donor termed biostimulation can alsobe employed to speed up remediation processes [137].However in many cases, the fertilization practice of contami-nated site using compost, nitrogen, phosphorus and carbonhas been unpredictable because it has been reported toeither enhance and not the degradation of pollutants[48,138]. In case, the degradative bacteria is absent in indige-nous microbial population, bioaugmentation can beemployed by introducing either wild type or geneticallymodified microbes into soil [48]. The laboratory scale resultsof seeding microbes for degradation of soil pollutants havebeen ambiguous [48].

The bioavailability of organic compounds is the mostimportant factor that determines the overall success of a bio-remediation process [47,50]. The availability of pollutant tothe organisms or bio-availability depends upon the chemicalnature of the pollutant (hydrophobicity, volatility, bindingcapacity, reactivity) and soil properties (particle size, waterand organic content, cation exchange capacity, pH). Manychemicals, plant=microbe exudates and secondary plantTa

ble

4.

Con

tin

ued

Xen

ob

ioti

cs

Vegeta

ted

pla

nts

Rem

oval

mech

an

ism

Rem

oval

Sta

tist

ics

Case

stu

dy

Refe

ren

ces

Lindan

e(H

CH

),M

ono-

chlo

robenze

ne

(MCB),

1,4

-dic

hlo

ro-

benze

ne

(DCB),

1,2

,4-

tric

hlo

robenze

ne

(TCB)

Ph

ragm

ites

Pla

ntupta

ke

––

[118]

Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep14 July 2013

products are potential enhancers of pollutant bio-availability.Artificially this can be improved by adding soil amendmentsin the form of surfactants like Triton-X 100, SDS [46,48,50]. Insoil polluted with organic chemicals, a combined stressmight enhance the degradation [47]. In the field of root tech-nology, certain strains of naturally occurring soil bacteriaAgrobacterium tumefaciens has been used to induce rootproliferation to increase the length and mass of plant rootsand thus the degradation [47].

Genetic alterations of plants and transgenic plants forimproved phytoremediation have already been developedand are spreading for field studies [46,47]. It can be doneby two methods (A) gene introduction (b) gene alteration.The most straightforward way is to add a broad host rangeplasmid having desired gene and a molecular marker whichcan be screened later on by a differentiable phenotypictrait.

Co-inoculation of a consortium of bacteria=or with algaeeach with different parts of catabolic degradation route,involved in the degradation of certain pollutant is oftenfound to be more efficient than the inoculation of singlestrains with the complete pathway [48]. Usually severalbacterial populations degrade pollutant more efficientlythan a single species or strain due to presence of partnerswhich use the various intermediates of the degradativepathway more efficiently (joint metabolism) [48,139]. Theclose proximity of different strains and the formation ofmixed micro colonies were observed only in the presenceof pollutant naphthalene, illustrating the formation of com-munities where various activities fulfill each other [48,134].However, a few reports have been collected where thedirect introduction of microbial strain or consortiumfor xenobiotic degradation activities is (bioaugmentedrhizoremediation) able to efficiently colonize the root[48,134–136].

Along with these, sample pre-treatment before entering aconstructed wetland can be done, for example, aerobic oranerobic digestion, filteration to remove suspended solids,pre-settlement tanks.

CONCLUSION

The application of constructed wetland harboring macro-phytes such as Phragmites, Typha, Juncus, Spartina, andScirpus is a promising method for cleaning up varied typesof effluents starting from domestic, agricultural and indus-trial sources revealing its potential in terms of significantreduction in BOD, COD, suspended solids, total solids, totalnitrogen, heavy metals along with remediation of xenobiot-ics, pesticides and polyaromatic hydrocarbons as the rootzone of these plants serves as an active and dynamic zonefor the microbial degradation of organic and sequestrationof inorganic pollutant resulting in successful treatment ofdomestic, textile, and other effluents. A significant amountof metals and other organic pollutants are found to accumu-late in plant parts, that is, stem leaves and roots. A progres-sive and novel approach can be applied to such systems toovercome loading limits and improving removal efficiencydue to seasonal variations. Some techniques like bioaug-mentation, biostimulation and genetically engineeredplant=microbe can be employed in this regard but on theground of genetic manipulations many ethical issues getraised as the biggest challenge in their use will be the hori-zontal transfer of plasmids or genes in the environment.The large scale adoption of this technology still requiresmuch fundamental and applied research needed to under-pin CW technology but when this would be taken in realconjunction with actual remediation schemes; it will achievethe multipurpose of wastewater treatment, eco-friendlyapproach and biomass reuse.

ACKNOWLEDGMENT

The authors thank the Director, Thapar University, Patiala,India, for providing the infrastructure and facilities.

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