Hybrid Treatment Systems for Dye Wastewater
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This article was downloaded by: [Kansas State University Libraries]On: 01 December 2013, At: 05:45Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Critical Reviews in EnvironmentalScience and TechnologyPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/best20
Hybrid Treatment Systems for DyeWastewaterFaisal Ibney Hai a , Kazuo Yamamoto b & Kensuke Fukushi ba Department of Urban Engineering , University of Tokyo , Tokyo,Japanb Environmental Science Center , University of Tokyo , Tokyo, JapanPublished online: 14 May 2007.
To cite this article: Faisal Ibney Hai , Kazuo Yamamoto & Kensuke Fukushi (2007) Hybrid TreatmentSystems for Dye Wastewater, Critical Reviews in Environmental Science and Technology, 37:4,315-377, DOI: 10.1080/10643380601174723
To link to this article: http://dx.doi.org/10.1080/10643380601174723
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Critical Reviews in Environmental Science and Technology, 37:315–377, 2007Copyright © Taylor & Francis Group, LLCISSN: 1064-3389 print / 1547-6537 onlineDOI: 10.1080/10643380601174723
Hybrid Treatment Systems for Dye Wastewater
FAISAL IBNEY HAIDepartment of Urban Engineering, University of Tokyo, Tokyo, Japan
KAZUO YAMAMOTO and KENSUKE FUKUSHIEnvironmental Science Center, University of Tokyo, Tokyo, Japan
Virtually all the known physicochemical and biological techniques
have been explored for treatment of extremely recalcitrant dye
wastewater; none, however, has emerged as a panacea. A single
universally applicable end-of-pipe solution appears to be unrealis-
tic, and combination of appropriate techniques is deemed imper-
ative to devise technically and economically feasible options. An
in-depth evaluation of wide range of potential hybrid technologies
delineated in literature along with plausible analyses of available
cost information has been furnished. In addition to underscoring
the indispensability of hybrid technologies, this article also endorses
the inclusion of energy and water reuse plan within the treatment
scheme, and accordingly proposes a conceptual hybrid dye wastew-
ater treatment system.
KEY WORDS: dye wastewater, decolorization, energy and waterreuse, hybrid treatment systems
1. INTRODUCTION
Large amounts of dyes are annually produced and applied in many differentindustries, including the textile, cosmetic, paper, leather, pharmaceutical, andfood industries.136 There are more than 100,000 commercially available dyeswith an estimated annual production of over 7 × 105 tons,179 15% of which islost during the dyeing process.70 The textile industry accounts for two-thirdsof the total dyestuff market136 and consumes large volumes of water and other
Address correspondence to Faisal Ibney Hai, Department of Urban Engineering, Univer-sity of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan. E-mail: faisal [email protected]
315
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316 F. I. Hai et al.
refractory chemicals for wet processing of textiles.210 The chemical reagentsused are very diverse in chemical composition, ranging from inorganic andlow-molecular-weight organic compounds to polymers.
The presence of even trace concentrations of dyes in effluent is highlyvisible and undesirable.79 The release of colored wastewater in the ecosystemis a remarkable source of esthetic pollution, eutrophication, and perturbationsin aquatic life.70 Dye effluent usually contains chemicals, including dye itself,that are toxic, carcinogenic, mutagenic, or teratogenic to various microbiolog-ical and fish species.50 Concern arises, as many dyes are made from knowncarcinogens such as benzidine and other aromatic compounds.179Also azoand nitro compounds have been reported to be reduced in sediments ofaquatic bodies, consequently yielding potentially carcinogenic amines thatspread in the ecosystem.211 The presence of dyes or their degradation prod-ucts in water can also cause human health disorders such as nausea, hem-orrhage, and ulceration of skin and mucous membranes,195 and can causesevere damage to the kidney, reproductive system, liver, brain, and centralnervous system.94 These concerns have led to new and/or stricter regulationsconcerning colored wastewater discharges, compelling the dye manufactur-ers and users to adopt “cleaner technology” approaches, for instance, devel-opment of new lines of ecologically safe dyeing auxiliaries and improvementof exhaustion of dyes on to fiber.79,180,210
Concomitant with the in-house multidimensional pollution minimizationefforts, a number of emerging material recovery/reuse and end-of-pipe de-colorization technologies are being proposed and tested at different stagesof commercialization. However, due to their synthetic origin and complexstructure deriving from the use of different chromophoric groups, dyes areextremely recalcitrant.179 Along with the recalcitrant nature of dye wastewa-ter, the frequent daily variability of characteristics of such wastewater adds tothe difficulty of treatment.77 Accordingly, despite the fact that virtually all theknown physicochemical and biological techniques have been explored fordecolorization,79 none has emerged as a panacea. Cost-competitive biologicaloptions are rather ineffective, while physicochemical processes are restrictedin scale of operation and pollution profile of the effluent. Table 1 lists theadvantages and disadvantages of different individual techniques. It appearsthat a single, universally applicable end-of-pipe solution is unrealistic, andcombination of different techniques is required to devise a technically andeconomically feasible option. In light of this researchers have put forward awide range of hybrid decolorization techniques. Figure 1 depicts a simplifiedrepresentation of the proposed combinations.
Although still mostly in laboratory stage of development, of late, a wealthof studies have been reported on implementation of advanced oxidation pro-cesses (AOPs) and their combinations for dye wastewater treatment. Manystudies have focused on different combinations of physicochemical treat-ments, which often have been employed by industries in simple, standalone
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TAB
LE1
.A
dva
nta
ges
and
Shortco
min
gsofIn
div
idual
Dye
Was
tew
ater
Tre
atm
entTe
chniq
ues
Pro
cess
Adva
nta
ges
Dis
adva
nta
ges
Sele
cted
refe
rence
s
Bio
logi
cal
Cost
-com
pet
itive
optio
n.D
irec
t,dis
per
se,an
dbas
icdye
shav
ehig
hle
velofad
sorp
tion
on
toac
tivat
edsl
udge
.
Dye
sar
ege
ner
ally
toxi
can
dve
ryre
sist
antto
bio
deg
radat
ion.A
cid
and
reac
tive
dye
sar
ehig
hly
wat
er-s
olu
ble
and
hav
epoor
adso
rptio
non
tosl
udge
.
160
Coag
ula
tion
Eco
nom
ical
lyfe
asib
le;sa
tisfa
ctory
rem
ova
lof
dis
per
se,su
lfur,
and
vatdye
s.Rem
ova
lis
pH
dep
enden
t;pro
duce
sla
rge
quan
tity
of
sludge
.M
aynotre
move
hig
hly
solu
ble
dye
s;unsa
tisfa
ctory
resu
ltw
ithaz
o,re
activ
e,ac
idan
dbas
icdye
s.
61,7
9,17
9
Act
ivat
edC
adso
rptio
nG
ood
rem
ova
lofw
ide
variet
yofdye
s,nam
ely,
azo,
reac
tive
and
acid
dye
s;es
pec
ially
suita
ble
for
bas
icdye
.
Rem
ova
lis
pH
dep
enden
t;unsa
tisfa
ctory
resu
ltfo
rdis
per
se,su
lfur,
and
vatdye
s.Reg
ener
atio
nis
expen
sive
and
invo
lves
adso
rben
tlo
ss;nec
essi
tate
sco
stly
dis
posa
l.
61,7
9,17
9
Ion
exch
ange
Adso
rben
tca
nbe
rege
ner
ated
with
outlo
ss,dye
reco
very
conce
ptu
ally
poss
ible
.Io
nex
chan
gere
sins
are
dye
-spec
ific;
rege
ner
atio
nis
expen
sive
;la
rge-
scal
edye
reco
very
cost
-pro
hib
itive
.17
9,19
6
Mem
bra
ne
filtr
atio
nA
ppro
priat
em
embra
ne
may
rem
ove
allty
pes
ofdye
san
dth
us
real
ize
reusa
ble
wat
erfr
om
dye
-bat
hef
fluen
t.
Conce
ntrat
edsl
udge
pro
duct
ion
and
cost
lym
embra
ne
repla
cem
entim
ped
ew
ides
pre
aduse
.36
Chem
ical
oxi
dat
ion
Initi
ates
and
acce
lera
tes
azo-b
ond
clea
vage
.Ther
modyn
amic
and
kinet
iclim
itatio
ns
along
with
seco
ndar
ypollu
tion
are
asso
ciat
edw
ithdiffe
rent
oxi
dan
ts.N
otap
plic
able
for
dis
per
sedye
s.N
eglig
ible
min
eral
izat
ion
poss
ible
,re
leas
eofar
om
atic
amin
esan
dad
diti
onal
conta
min
atio
nw
ithch
lorine
(in
case
of
NaO
Cl)
issu
spec
ted.
179,
196
Adva
nce
doxi
dat
ion
pro
cess
es,A
OPs
Gen
erat
ea
larg
enum
ber
ofhig
hly
reac
tive
free
radic
als
and
by
far
surp
ass
the
conve
ntio
nal
oxi
dan
tsin
dec
olo
riza
tion.
AO
Ps
inge
ner
alm
aypro
duce
further
undes
irab
leto
xic
by
pro
duct
san
dco
mple
tem
iner
aliz
atio
nm
aynotbe
poss
ible
.Pre
sence
sofra
dic
alsc
aven
gers
reduce
effici
ency
ofth
epro
cess
esso
me
ofw
hic
har
epH
dep
enden
t.Cost
-pro
hib
itive
atth
eir
pre
sentst
age
of
dev
elopm
ent.
(Con
tin
ued
on
nex
tpa
ge)
317
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TAB
LE1
.A
dva
nta
ges
and
Shortco
min
gsO
fIn
div
idual
Dye
Was
tew
ater
Tre
atm
entTe
chniq
ues
(Con
tin
ued
)
Pro
cess
Adva
nta
ges
Dis
adva
nta
ges
Sele
cted
refe
rence
s
UV
/O3
Applie
din
gase
ous
stat
e,no
alte
ratio
nofvo
lum
e.G
ood
rem
ova
lofal
most
allty
pes
ofdye
s;es
pec
ially
suita
ble
for
reac
tive
dye
s.In
volv
esno
sludge
form
atio
n,nec
essi
tate
ssh
ort
reac
tion
times
.
Rem
ova
lis
pH
dep
enden
t(n
eutral
tosl
ightly
alka
line)
;poor
rem
ova
lofdis
per
sedye
s.Pro
ble
mat
ichan
dlin
g,im
pose
additi
onal
load
ing
ofw
ater
with
ozo
ne.
Neg
ligib
leor
no
CO
Dre
mova
l.H
igh
cost
of
gener
atio
nco
uple
dw
ithve
rysh
ort
hal
f-lif
ean
dga
s-liq
uid
mas
stran
sfer
limita
tion;su
ffer
sfr
om
UV
lightpen
etra
tion
limita
tion.In
crea
sed
leve
loftu
rbid
ityin
effluen
ts.
61,7
3,79
,90
,140
,17
9
UV
/H2O
2In
volv
esno
sludge
form
atio
n,nec
essi
tate
ssh
ort
reac
tion
times
and
reduct
ion
ofCO
Dto
som
eex
tentm
aybe
poss
ible
.
Notap
plic
able
for
alldye
types
,re
quires
separ
atio
nof
susp
ended
solid
and
suffer
sfr
om
UV
lightpen
etra
tion
limita
tion.Lo
wer
pH
required
tonulli
fyef
fect
of
radic
alsc
aven
gers
.
73,1
40
Fento
nre
agen
tEffec
tive
dec
olo
riza
tion
ofboth
solu
ble
and
inso
luble
dye
s;ap
plic
able
even
with
hig
hsu
spen
ded
solid
conce
ntrat
ion.Si
mple
equip
men
tan
dea
syim
ple
men
tatio
n.Red
uct
ion
ofCO
D(e
xcep
tw
ithre
activ
edye
s)poss
ible
.
Effec
tive
with
innar
row
pH
range
of<
3.5;
and
invo
lves
sludge
gener
atio
n.Com
par
ativ
ely
longe
rre
actio
ntim
ere
quired
79,14
0,17
9,20
3
Photc
atal
ysis
No
sludge
pro
duct
ion,co
nsi
der
able
reduct
ion
of
CO
D,pote
ntia
lofso
lar
lightutil
izat
ion.
Ligh
tpen
etra
tion
limita
tion,fo
ulin
gofca
taly
sts,
and
pro
ble
moffine
cata
lyst
separ
atio
nfr
om
the
trea
ted
liquid
(slu
rry
reac
tors
)
105
Ele
ctro
chem
ical
Effec
tive
dec
olo
riza
tion
ofso
luble
/inso
luble
dye
s;re
duct
ion
ofCO
Dposs
ible
.N
otaf
fect
edby
pre
sence
ofsa
ltin
was
tew
ater
.
Sludge
pro
duct
ion
and
seco
ndar
ypollu
tion
(fro
mch
lorinat
edorg
anic
s,hea
vym
etal
s)ar
eas
soci
ated
with
elec
troco
agula
tion
and
indirec
toxi
dat
ion,re
spec
tivel
y.D
irec
tan
odic
oxi
dat
ion
requires
further
dev
elopm
ent
for
indust
rial
acce
pta
nce
.H
igh
cost
ofel
ectric
ityis
anim
ped
imen
t.Effi
cien
cydep
ends
on
dye
nat
ure
.
40,1
79
Sonoly
sis
Additi
on
ofch
emic
alad
diti
ves
notre
quired
and
hen
cedoes
notpro
duce
exce
sssl
udge
.Req
uires
alo
tofdis
solv
edga
s(O
2);
com
ple
tedec
olo
ratio
nan
dm
iner
aliz
atio
nby
sonifi
catio
nal
one
are
notec
onom
ical
atpre
sentle
velofre
acto
rdev
elopm
ent.
2,11
Ioniz
ing
radia
tion
No
sludge
pro
duct
ion;ef
fect
ive
oxi
dat
ion
atla
bsc
ale.
Req
uires
alo
tofdis
solv
edO
2;co
mple
tedec
olo
ratio
nan
dm
iner
aliz
atio
nby
stan
dal
one
applic
atio
nnot
poss
ible
.Ener
gyef
fici
entsc
ale-
up
yetto
be
achie
ved.
179
Wet
air
oxi
dat
ion,
WA
OW
ell-es
tablis
hed
tech
nolo
gyes
pec
ially
suita
ble
for
effluen
tto
odilu
tefo
rin
ciner
atio
nan
dto
oto
xic
and/o
rco
nce
ntrat
edfo
rbio
logi
caltrea
tmen
t.
Com
ple
tem
iner
aliz
atio
nnotac
hie
ved,as
low
erm
ole
cula
rw
eigh
tco
mpounds
are
notam
enab
leto
WA
O.H
igh
capita
lan
doper
atin
gco
sts
are
asso
ciat
edw
ithel
evat
edpre
ssure
and
tem
per
ature
emplo
yed.
10,1
1
318
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Hybrid Treatment Systems for Dye Wastewater 319
FIGURE 1. Simplified representation of broad spectrum of combinations proposed in theliterature.
manner. Combinations of conventional physicochemical techniques with theAOPs have also appeared as attractive options. The biological systems, inaddition to varieties of combinations among themselves, have also been ex-plored in fusion with virtually all sorts of physicochemical and advancedoxidation processes.
This article offers a comprehensive review of the potential hybrid tech-nologies delineated in literature for treatment of dye wastewater in generaland textile wastewater in particular. Analogous to the aforementioned trends,the combinations have been outlined under three broad categories: com-bination among AOPs, combination of physicochemical treatments amongthemselves and those with the AOPs, and, with paramount importance, thecombination of biological systems with conventional physicochemical pro-cesses and AOPs (Figure 1). Before elaborating on the combinations, the ba-sic principles and limitations of relevant individual techniques are discussedbriefly. Based on the array of potential hybrid technologies and the avail-able cost information, a conceptual on-site textile dye wastewater treatmentsystem integrated with energy and water recovery/reuse has been proposed.
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320 F. I. Hai et al.
2. COMBINATION AMONG AOPs
While advanced oxidation processes (AOPs) have been studied extensivelyboth for recalcitrant wastewater in general and dye wastewater in particu-lar, their commercialization has yet not been realized because of prevailingbarriers.72,73 These processes are cost prohibitive and complex at the presentlevel of their development.163 Additional impediment exists in treatment ofdye wastewater with relatively higher concentration of dyes, as AOPs areonly effective for wastewater with very low concentrations of organic dyes.Thus, significant dilution is necessary as a facility requirement. The pres-ence of dye additives/impurities such as synthetic precursors, by-products,salts, and dispersing agents in commercial dye bath recipe causes furtherreduction in process efficiency.11,149,152 Although the usual small-scale labo-ratory investigations reveal encouraging results, such studies are insufficientto cast light on practical feasibility of AOPs. For example, in photochemi-cal/photocatalytic decoloration, most of the investigations involve reactorsranging from as small as few tens of milliliters (e.g., 40 ml38) to several hun-dreds of milliliters (e.g., 250 ml146) or at best few liters (e.g., 4 L64), whichare inadequate to explicitly address the light penetration issue, the inherentdrawback of this technology. Only a handful of pilot plant explorations withless than persuasive192,193 or moderate187results have been documented. Re-ports on full-scale application of sole AOP treatment of dye bath effluentsare apparently lacking.
Nevertheless, such processes generate a large number of highly reactivefree radicals and by far surpass the conventional oxidants in decolorization.The conventional oxidants have more significant thermodynamic and kineticlimitations.46 For the AOPs, the basic reaction mechanism is the generation offree radicals and subsequent attack by these on the pollutant organic species.Hence it is strongly believed that their combination will result in more freeradicals, thereby increasing the rates of reactions.72,73 Moreover, some of thedrawbacks of the individual AOPs may be eliminated by the characteristicsof other AOPs. The cost/energy efficiency, however, will be dependent onthe operating conditions and the type of the effluent. Table 2 furnishes aquasi-exhaustive list of typical examples of studies on combinations amongAOPs for dye wastewater treatment. Information on type of associated dyeshas been included wherever available.
2.1. Different Photochemical Processes
The photo-activated chemical reactions are characterized by a free radi-cal mechanism initiated by the interaction of photons of a proper energylevel with the chemical species present in the solution. Generation of rad-icals through ultraviolet (UV) radiation by the homogenous photochemical
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TAB
LE2
.Typ
ical
Exa
mple
sofCom
bin
atio
ns
Am
ong
AO
Ps
for
Dye
Was
tew
ater
Tre
atm
ent
Tech
nolo
gyD
ye/w
aste
wat
erD
etai
lsRef
eren
ce(y
ear)
UV
/O3
2-nap
hth
alen
esulfonat
e[A
zoD
yein
term
edia
te]
Min
eral
izat
ion
of2-
NS
via
ozo
nat
ion
(40
mg/
L)is
rem
arka
bly
enhan
ced
by
UV
radia
tion
(60.
35W
/m2,25
4nm
),trip
ling
the
rate
.N
otm
uch
diffe
rence
in2-
NS
dec
om
posi
tion.
39(2
002)
UV
/O3,U
V/H
2O
2A
cid
N=N
-re
d1/
bla
ck1/
red14
/red
18/o
range
10/y
ello
w17
/yel
low
23;
Direc
tN=N
yello
w4
Dec
olo
ratio
n(2
0m
g/L
dye
):10
0%in
10m
inby
O3(6
L/m
inO
2)
with
/with
outU
V;80
%in
25m
inby
H2O
2–U
V.N
eglig
ible
enhan
cem
entofozo
nat
ion
by
UV
(low
pow
er)
due
toab
sorp
tion
of
most
UV
by
dye
.D
ilutio
nofsa
mple
and/o
roptim
um
reac
tor
des
ign
reco
mm
ended
.
192
(199
5)
UV
/H2O
2H
ispam
inB
lack
CA
[Direc
tN=N
Bla
ck22
]U
V(1
25W
)-H
2O
2(5
65.8
mg/
L,16
.6m
M):
Com
ple
tedec
olo
ratio
n(3
5m
in)
&82
%TO
Cre
mova
l(6
0m
in)
for
40m
g/L
dye
atnat
ura
lpH
(7.5
),al
though
subse
quen
tto
xici
tyte
stre
com
men
ded
.
46(2
002)
UV
/H2O
2A
cid
dye
[ora
nge
8N=N
/blu
e74
C=C
,M
ethyl
ora
nge
N=N
]Rem
ova
lby
Only
UV
(15
W,25
3.7
nm
,in
ciden
tphoto
nflux
=6.
1×
10−6
Ein
stei
ns−1
,4.
54≤
pH
≤5.
5)an
donly
H2O
2in
abse
nce
ofU
Vw
asneg
ligib
le.Com
bin
ed:D
ecolo
riza
tion
rate
rise
sby
incr
easi
ng
the
initi
aldosa
geofH
2O
2up
toa
criti
calva
lue
([H
2O
2]/
[dye
]=
50–7
0)bey
ond
whic
hit
isin
hib
ited.
4(2
003)
UV
/H2O
2Rea
ctiv
e-re
d12
0N=N
/bla
ck5N
=N
/yel
low
84N
=NU
V(1
5W
)/H
2O
2(o
ptim
um
dose
24.5
mm
ol/
l):15
min
:[D
ecolo
riza
tion
>65
%,CO
Dre
mova
l=
40–7
0%],
60m
in:[D
ecolo
riza
tion
>99
%];
Deg
radat
ion
by
pro
duct
sunobje
ctio
nab
le.
152
(200
2)
UV
/H2O
2an
dso
lar/
H2O
2
Chlo
rotria
zine
Rea
ctiv
eN=N
Ora
nge
4D
yere
mova
l(0
.5m
mol/
L),15
0m
in,pH
3:U
V(6
4W,36
5nm
)-H
2O
2(1
0m
mol)
=88
.68%
dec
olo
riza
tion
,59
.85%
deg
radat
ion.
Sunlig
ht–
H2O
2=
80.1
5%dec
olo
riza
tion,50
.91%
deg
radat
ion.D
yeau
xilia
ries
like
Na 2
CO
3,N
aOH
seriousl
yre
tard
dec
olo
ratio
nra
tew
hile
NaC
ldoes
not.
149
(200
4)
O3
follo
wed
by
UV
/H2O
2
Was
tew
ater
from
cotton
&poly
este
rfiber
dye
ing
text
ilem
illU
nder
nat
ura
lpH
(10.
66)
5m
inpre
ozo
nat
ion
(293
mg/
L),re
movi
ng
hig
hU
V-a
bso
rbin
gco
mponen
ts(6
0%re
duct
ion
inU
V25
4),
acce
lera
ted
subse
quen
t55
min
H2O
2(5
0m
mol/
L)-U
V(2
5W
)trea
tmen
t,en
han
cing
itsCO
D&
TO
Cre
mova
lef
fici
ency
by
afa
ctor
of13
&4,
resp
ectiv
ely;
the
com
bin
edtrea
tmen
tyi
eldin
g25
%CO
D,50
%TO
C&
com
ple
teco
lor
rem
ova
l(I
niti
alCO
D=
1476
mg/
L;TO
C=
336
mg/
L).
8(2
001)
UV
/H2O
2/O
3W
aste
wat
erco
nta
inin
gdis
per
sedye
stuff
&pig
men
ts99
%CO
D(I
niti
ally
930
mg/
L)an
d96
%co
lor
rem
ova
lin
90m
in[p
H=
3;H
2O
2=
200
mg/
L;O
3=
2g/
h;15
Wla
mp,25
4nm
].O
ver
90%
rem
ova
lby
UV
/O3
with
less
cost
due
tono
requirem
entofpH
adju
stm
entan
dH
2O
2.
12(2
004)
(Con
tin
ued
on
nex
tpa
ge)
321
Dow
nloa
ded
by [
Kan
sas
Stat
e U
nive
rsity
Lib
rari
es]
at 0
5:45
01
Dec
embe
r 20
13
TAB
LE2
.Typ
ical
Exa
mple
sofCom
bin
atio
ns
Am
ong
AO
Ps
for
Dye
Was
tew
ater
Tre
atm
ent
(Con
tin
ued
)
Tech
nolo
gyD
ye/w
aste
wat
erD
etai
lsRef
eren
ce(y
ear)
Fe+2
/O3
Sim
ula
ted
dis
per
sedye
bat
h(
CI
dis
per
se-vi
ole
t93
1,blu
e29
1;tw
om
ore
azo
dye
san
dco
mpounds)
95%
colo
r(D
yes
=0.
5g/
L),48
%CO
D(initi
ally
=37
84m
g/L)
rem
ova
lan
d10
times
impro
vem
entin
BO
D5/C
OD
ratio
atnat
ura
lac
idic
pH
of
dye
bat
h(
3.6
mM
Fe+2
;[F
e+2]:
[O3]=
1:14
;Fe
SO4.7
H2O
=10
00m
g/L)
.N
eglig
ible
TO
Cre
mova
lis
due
tolo
wO
3dose
of14
g/L.
9(2
001)
UV
/Fen
ton
Dis
per
seN
=Nre
d35
485
%co
lor
rem
ova
l(D
ye=
100
mg/
L)&
90%
CO
Dre
mova
lw
ithin
10m
inw
ith24
.5m
molH
2O
2/L
and
1.22
5m
molFe
SO4/L
atpH
=3,
resu
lting
effluen
thav
ing
only
7.29
%in
hib
ition
inbio
lum
ines
cence
test
.Pre
sence
ofdis
per
sing
agen
tre
duce
sre
mova
lef
fici
ency
.
153
(200
3)
UV
/Fen
ton
Rea
ctiv
eN
=Nbrilli
antre
dX
-3B
Stab
ledec
olo
ratio
n(D
ye=
7.7
×10
−5M
)w
ithin
20m
inw
ith[H
2O
2]=
18x
10−4
M,[F
e+2]or
[Fe+3
]=
1.1
×10
−4M
,75
WU
V(λ
<32
0nm
)la
mp.U
seofFe
+2is
pre
fera
ble
toFe
+3bec
ause
offa
ster
reac
tion
rate
with
H2O
2an
dev
olu
tion
ofH
O.in
stea
dofH
O2.
226
(200
1)
Sola
r/Fe
nto
nO
range
II(A
cid
N=N
ora
nge
7)D
ecolo
ratio
nofhig
hly
conce
ntrat
ed(2
.9m
M≡
0.8
g/L)
dye
inle
ssth
an2
han
d95
%m
iner
aliz
atio
nw
ithin
8h
by
aso
lar
sim
ula
tor
(90
mW
cm−2
)an
dal
soby
nat
ura
lsu
nlig
ht(8
0m
Wcm
−2)
with
0.92
mM
Fe+3
and
10m
MH
2O
2/h
r[p
H=
2].
20(1
996)
Sola
r/Fe
nto
nM
onore
activ
eN=N
Pro
cion
red
H-E
7B,
Het
ero-b
irea
ctiv
eN=N
Red
cibac
ron
FN-R
,St
andar
dtric
hro
mat
icm
ixtu
re
Sunlig
ht,
supply
ing
hig
her
num
ber
ofphoto
ns
(3–4
x10
−3W
cm−2
)th
anth
elo
wpow
erar
tifici
also
urc
e(3
50nm
,6
W,1.
3x
10−4
Wcm
−2),
resu
lted
infa
ster
com
ple
tedec
olo
ratio
n(1
5–30
min
)an
dco
mple
te(o
rnea
r)TO
Cre
mova
l(2
0–60
min
)fo
rdye
conce
ntrat
ion
of10
0m
g/L
with
10m
g/L
Fe+2
and
100–
250
mg/
LH
2O
2[p
H=
3].
207
(200
4)
Cu(I
I)/g
luar
icac
id/H
2O
2
Direc
tChic
ago
sky
blu
eN=N
,M
ethyl
ora
nge
N=N
,Rea
ctiv
eN=N
bla
ck5;
Poly
AQ
B-4
11,Rea
ctiv
eAQ
blu
e2,
RB
BR
AQ,A
crid
in(B
asic
)AQ
ora
nge
;A
zure
blu
eTH,Cry
stal
viole
tTPM
Ove
r90
%dec
olo
riza
tion
of10
0ppm
dye
with
in24
h(7
0–80
%w
ithin
firs
t6
h)
with
10m
MCuSO
4,20
0m
MH
2O
2an
dlo
wdose
ofgl
uca
ric
acid
(15
mM
).In
sensi
tive
topH
,unlik
eFe
nto
nre
actio
n.
212
(200
4)
UV
/O3/T
iO2
Text
ileef
fluen
tco
nta
inin
gRea
ctiv
eN=N
dye
Rem
ova
ls(6
0m
in)-
Photo
cata
lysi
s(0
.1g/
Lan
atas
eTiO
2,12
5W
,fluen
cyra
te31
.1J
m2
s−1,pH
=11
):Colo
r=
90%
,TO
C=
50%
;O
zonat
ion
(pH
=11
,14
mg/
L):Colo
r=
60%
,TO
C=
neg
ligib
le;Com
bin
ed:
Colo
r=
100%
,TO
C>
60%
,To
xici
ty=
50%
146
(200
0)
UV
/H2O
2/T
iO2
Eosi
nY
XN
Enhan
ced
dec
olo
ratio
n(1
00%
for
50m
g/L
dye
)&
min
eral
izat
ion
(95%
)in
1h
(19
Wla
mp,1g
/LTiO
2,10
0m
g/L
H2O
2,pH
=5.
4)al
ong
with
85%
reduct
ion
into
xici
ty.
173
(200
3)
322
Dow
nloa
ded
by [
Kan
sas
Stat
e U
nive
rsity
Lib
rari
es]
at 0
5:45
01
Dec
embe
r 20
13
Sola
r/H
2O
2/p
oly
mer
icm
etal
loporp
hyr
ins
Acr
idin
(Bas
ic)A
Qora
nge
%[D
ecolo
ratio
n,D
egra
dat
ion]:
Hg
lam
p(4
50W
,8
h)
Cat
alys
is(3
mg/
35m
l)w
ithH
2O
2(0
.4g/
L)=
[87,
92];
with
outH
2O
2=
[77,
86].
Sola
rlig
ht(
3h)
Cat
alys
isw
ithoutH
2O
2=
[77,
90].
Dye
=13
.3m
g/L,
hig
hpH
favo
rable
.
38(2
002)
Puls
edst
ream
erco
rona
dis
char
ge(e
lect
rica
l)/H
2O
2
Rhodam
ine
BXN
(Bas
ic),
Aci
dN
=NM
ethyl
ora
nge
,D
irec
tN=N
Chic
ago
sky
blu
e
Puls
edhig
hvo
ltage
(20
kV,25
Hz)
elec
tric
aldis
char
gein
wat
er,
yiel
din
gphoto
dis
soci
atio
nofad
ded
H2O
2(8
.8×
10−4
mol/
L),sh
ow
eden
han
ced
dec
olo
ratio
nra
te(1
00%
for
10m
g/L
dye
in60
min
)as
com
par
edto
indiv
idual
pro
cess
-per
orm
ance
s.
200
(200
2)
Photo
elec
troch
emic
alM
ethyl
ene
blu
eTH
Chem
ical
syner
gism
ofphoto
chem
ical
&el
ectroch
emic
alpro
cess
esyi
elded
enhan
ced
dec
olo
ratio
n(9
5%),
CO
Dre
mova
l(8
7%)
&TO
Cre
mova
l(8
1%)
in30
min
[Dye
=1
mm
ol/
L;50
0W
lam
p,6.
64m
Wcm
−2;1
gTiO
2/2
00m
l;30
VD
C;N
atura
lpH
(6.6
)].
6(2
002)
Mic
row
ave
(MW
)/Photo
cata
lysi
sRhodam
ine
BXN
(Bas
ic)
Inco
ntras
tto
neg
ligib
lere
mova
lby
MW
(300
W),
or
less
rem
ova
lby
photo
cata
lysi
s(7
5W,0.
3mW
cm−2
;30
mg
TiO
2/3
0m
l)al
one,
com
bin
edpro
cess
achie
ved
97%
dec
olo
ratio
n(D
ye=
0.05
mM
)an
d73
%TO
Cre
mova
lw
ithin
3h
atpH
=5.
5.
84(2
002)
Photo
elec
troca
taly
sis
Rea
ctiv
eN=N
brilli
antora
nge
K-R
Dec
olo
ratio
nan
dTO
Cre
mova
lofdye
(0.5
mM
)in
0.5
mm
oll−1
NaC
lso
lutio
nw
ithin
60m
in(N
atura
lpH
):i)
Adso
rptio
non
pac
ked
mat
eria
l:9%
,–
;ii)
Photo
cata
lysi
s[T
iO2
(anta
se=
70%
)-co
ated
quar
tzsa
nd,50
0W
hig
h-p
ress
ure
mer
cury
lam
p]:
70%
,20
%;iii
)Ele
ctro
-oxi
dat
ion
[30.
0V
DC
cell
volta
ge,re
actio
nflow
rate
=19
0m
lm
in−1
,0.
05M
Pa
airfl
ow
]:77
%,7%
;iv
)Photo
elec
troca
taly
sis:
96%
,38
%.O
bvi
ous
enhan
cem
entef
fect
(unlik
ephoto
cata
lysi
s)ofsa
ltin
solu
tion.
238
(200
3)
UV
/ele
ctro
-Fen
ton
Rea
ctiv
eN=N
Red
120
TO
Cre
mova
l[1
80m
in]:
30%
;D
ecolo
ratio
n[3
0m
in]:
75–8
5%fo
r60
-100
mg/
Lco
nce
ntrat
ion;Lo
wef
fici
ency
due
tora
dic
alsc
aven
ging
by
the
grap
hite
cath
ode.
Det
oxi
fica
tion
[90
min
]:Sa
fely
dis
posa
ble
.
116
(200
4)
Gam
ma
irra
dia
tion/H
2O
2
Rea
ctiv
eTC
blu
e15
(Chro
zoltu
rquose
blu
eG
),Rea
ctiv
eN=N
bla
ck5
(Chro
zolbla
ck5)
H2O
2,yi
eldin
g.O
Hby
reac
ting
with
hyd
rate
del
ectron
form
edin
radio
lysi
sofw
ater
,ac
hie
ved
enhan
ced
dec
olo
ratio
n(1
00%
,50
ppm
dye
)an
dCO
Dre
mova
l(7
6–80
%)
with
1an
d15
kGy
dose
sfo
rRB
5an
dRB
15,re
spec
tivel
y,dec
olo
ratio
n(%
)bei
ng
the
hig
hes
tat
the
low
estdose
rate
(0.1
4kG
y/h).
194
(200
2)
(Con
tin
ued
on
nex
tpa
ge)
323
Dow
nloa
ded
by [
Kan
sas
Stat
e U
nive
rsity
Lib
rari
es]
at 0
5:45
01
Dec
embe
r 20
13
TAB
LE2
.Typ
ical
Exa
mple
sofCom
bin
atio
ns
Am
ong
AO
Ps
for
Dye
Was
tew
ater
Tre
atm
ent
(Con
tin
ued
)
Tech
nolo
gyD
ye/w
aste
wat
erD
etai
lsRef
eren
ce(y
ear)
Sonoly
sis/
MnO
2A
cid
N=N
red
BSo
nic
atio
n(5
0kH
z,15
0W
)en
han
ced
oxi
dat
ion
pro
per
tyofM
nO
2
(1g/
L)by
impro
ving
mas
stran
sfer
,re
mova
lofpas
siva
ting
oute
roxi
de
laye
r&
pro
duct
ion
ofH
2O
2,ev
entu
ally
real
izin
g94
.93%
dec
olo
riza
tion
(arg
on
atm
osp
her
e)an
d48
.12
%TO
Cre
mova
l(o
xyge
nat
mosp
her
e)[in
itial
pH
=3,
240
min
].
68(2
003)
Sonoly
sis
/Fen
ton
reac
tion
Aci
dN
=NM
ethyl
ora
nge
Additi
on
ofFe
SO4
([Fe
+2]=
0.1–
0.5
mM
)re
sulte
din
Fento
n’s
reac
tion
with
H2O
2ev
olv
ing
from
sim
ulta
neo
us
sonifi
catio
n(5
00kH
z,50
W)
and
achie
ved
3-fo
ldin
crea
sein
dec
olo
ratio
n(1
5m
in,10
μM
dye
)an
dTO
Cre
mova
l(5
0%,20
min
)as
com
par
edto
sonifi
catio
nonly
.
93(2
000)
Sonoly
sis/
O3
C.I
Rea
ctiv
eN=N
bla
ck5
(RB
B)
Com
bin
edso
noly
sis
(520
kHz)
and
ozo
nat
ion
(irr
adia
tion
inte
nsi
ty,O
3
inputan
dvo
lum
ew
ere
1.63
Wcm
−2;50
Lh/1
;an
d60
0m
l)sh
ow
edsy
ner
gist
icef
fect
,doublin
gth
edec
olo
riza
tion
(100
%,15
min
)an
dm
iner
aliz
atio
n(7
6%,1
h)
rate
.
90(2
001)
Sonoly
sis/
O3
Aci
dN
=NM
ethyl
ora
nge
Com
bin
edso
noly
sis
(500
kHz,
50W
)an
dozo
nat
ion
(50V
)sh
ow
edsy
ner
gist
icef
fect
(dea
den
dbyp
roduct
sofone
pro
cess
bei
ng
deg
raded
by
the
oth
er)
yiel
din
gin
stan
tdec
olo
ratio
n(1
0μ
Mdye
)an
d80
%m
iner
aliz
atio
n(3
h)
asco
mpar
edto
20-3
0%by
stan
d-a
lone
applic
atio
n.
53(2
000)
Sonoly
sis/
UV
/O3
C.I
Aci
dN
=Nora
nge
7Enhan
ced
O3
(40
g/m
3)
diffu
sion
by
mec
han
ical
effe
cts
ofultr
asound
(520
kHz,
600
W)
&th
ephoto
lysi
s(1
08W
)ofultr
asound-g
ener
ated
H2O
2to
pro
duce
.O
Hle
dto
com
ple
tedec
olo
ratio
n(D
ye=
57μ
M),
40%
TO
Cre
mova
l&
anim
pro
vem
entofB
OD
5/T
OC
from
zero
to0.
45w
ithin
60m
in(initi
alpH
=5.
5).
206
(200
4)
Sonoly
sis
/H2O
2Vin
ylsu
lfone
reac
tive
dye
s[C
.IRea
ctiv
e-Yel
low
15N
=N,Red
22N
=N,
Blu
e28
,B
lue
220,
Bla
ck5N
=N;
Rem
azoldar
kbla
ckN
150%
]
Com
bin
edso
noly
sis
(20
kHz)
and
H2O
2(3
.49
mol/
L)sh
ow
edsy
ner
gist
icef
fect
,doublin
gth
edec
olo
riza
tion
(90–
99%
dep
endin
gon
dye
,4
h)
rate
.
216
(200
3)
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Sonoly
sis/
UV
/H2O
2Cupro
phen
yle
yello
wRLC
=CSo
nic
atio
n(3
20kH
z)dra
mat
ical
lyen
han
ced
oxi
dat
ion
effici
ency
of
UV
(6at
11W
)+
H2O
2(0
.1m
l/L)
syst
em(p
H=
11)
by
impro
ving
oxy
gen
upta
ke&
tran
sfer
,th
eco
mbin
edpro
cess
achie
ving
94%
dye
(0.1
g/L)
rem
ova
lin
60m
info
llow
ing
pse
udo
firs
t-ord
erki
net
ics.
63(1
999)
Sonoly
sis
/UV
/TiO
2N
aphth
olblu
ebac
kN=N
Sim
ulta
neo
us
or
sequen
tialso
noly
sis
(640
kHz,
240
W)
and
photo
cata
lysi
s(1
g/L
TiO
2)
show
edad
diti
veef
fect
on
dec
olo
ratio
n(1
00%
in20
0m
in;50
μM
dye
)w
hile
,in
term
sofm
iner
aliz
atio
n,
sim
ulta
neo
us
applic
atio
n(5
0%,4
h;80
%,12
h),
due
tom
ass
tran
sfer
impro
vem
entofre
acta
nts
&pro
duct
sto
and
from
TiO
2su
rfac
e,per
form
edbet
ter
than
sequen
tialap
plic
atio
n(<
20%
,h;50
%,1
h).
198
(200
0)
Sonoly
sis/
UV
/TiO
2A
cid
N=N
-re
d1,
Ora
nge
8Si
multa
neo
us
sonoly
sis
(20
kHz,
15W
)an
dphoto
cata
lysi
s(0
.1g/
LTiO
2)
show
edsy
ner
gist
icef
fect
on
dec
olo
ratio
n/d
egra
dat
ion
(2.5
×10
−5M
dye
)due
topro
motin
gde-
aggr
egat
ion
ofTiO
2,des
orp
tion
ofre
acta
nts
&pro
duct
sfr
om
TiO
2su
rfac
e&
mai
nly
by
scis
sion
ofpro
duce
dH
2O
2,
ther
eby,
incr
easi
ng
oxi
diz
ing
spec
ies
inaq
ueo
us
phas
e.
148
(200
3)
Sonoly
sis
UV
/H2O
2C.I
reac
tiveN
=Nre
d12
0So
nifi
catio
n(3
20kH
z)si
gnifi
cantly
enhan
ced
the
dec
olo
ratio
n(D
ye=
0.1
g/L)
effici
ency
ofU
V/H
2O
2.H
igher
flow
rate
(insu
ffici
ent
irra
dia
tion)
nec
essi
tate
dhig
her
dosi
ng
rate
ofH
2O
2.
64(2
001)
Sonoel
ctro
lysi
sA
cid
N=N
sandola
nYel
low
Ele
ctro
-oxi
dat
ion
ofdye
(50
mg/
L)in
salin
eso
lutio
n(0
.01
mol/
LN
aCl)
invo
lvin
gin
situ
gener
atio
nofhyp
och
lorite
ion
was
enhan
ced
usi
ng
ultr
asound
(20
kHz,
22W
)w
hen
carr
ied
outin
ase
mis
eale
dce
ll,w
hic
hm
inim
ized
the
effe
cts
ofultr
asonic
deg
assi
ng.
135
(200
0)
Note
.D
iffe
rentdye
chro
mophore
s:N
=N:Azo
,AQ
:Anth
raquin
one,
TPM
:Triphen
ylm
ethan
edye
,TH:Thia
zine;
XN:Xan
then
e;C=C
:Stil
ben
edye
;TC:Phth
alocy
anin
e.
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326 F. I. Hai et al.
degradation of oxidizing compounds like hydrogen peroxide,4 ozone,39 orFenton’s reagent152 has been frequently reported to be superior to solelyUV radiation or sole utilization of such oxidants. Highly UV absorbing dyewastewater may inhibit process efficiency by limiting penetration of UVradiation, necessitating use of high-intensity UV lamps192 and/or a specif-ically designed reactor.119 One example of an appropriate reactor is a re-actor that generates internal liquor flow currents bringing all liquor com-ponents into close proximity to the UV source. Conversely, a thin-channelcoiled reactor may also be used.187 Arslan et al.8 proposed pre-ozonationto remove high UV-absorbing components, and thereby to accelerate subse-quent H2O2–UV treatment by increasing UV penetration. Simultaneous useof UV/H2O2/O3 has also been reported to yield enhanced reaction kinetics.12
However, this entailed additional cost as compared to UV/H2O2 or UV/O3,and hence such use is recommended to be weighed against degree of re-moval required and associated cost. As activators of oxidants like O3or H2O2,a handful of studies have put forward other alternatives to UV, namely,reduced transition metals,9 gamma irradiation,80,194 humic substances,82
etc.An alternative way to obtain free radicals is the photocatalytic mecha-
nism occurring at the surface of semiconductors, that is, heterogeneous pho-tocatalysis. Various chalcogenides (oxides such as TiO2, ZnO, ZrO2, CeO2,etc. or sulfides such as CdS, ZnS, etc.) have been used as photocatalysts so farin different studies. However, titanium dioxide (TiO2) in the anatase form isthe most commonly used photocatalyst, as it has reasonable photoactivity.143
Moreover, it also furnishes the advantages of being insoluble, comparativelyinexpensive, and nontoxic, together with having resistance to photocorrosionand biological immunity.6 The photocatalytic process can be carried out bysimply using slurry of the fine catalyst particles dispersed in the liquid phasein a reactor or by using supported/immobilized catalysts. Limitations of slurryreactors are low irradiation efficiency due to the opacity of the slurry, foulingof the surface of the radiation source due to the decomposition of the catalystparticles, and the requirement that the ultrafine catalyst to be separated fromthe treated liquid. On the other hand, drawbacks of supported photocatal-ysis are scouring of films comprising immobilized powders of catalyst andreduced catalyst area to volume ratio. Recently fluidized bed reactors havebeen reported to take advantages of better use of light, ease of temperaturecontrol, and good contact between target compound and photocatalysts overslurry reactors or fixed bed reactors.
Besides sole photocatalysis, reports on utilization of photocatalysis inpresence of O146
3 or H2O2,200 exhibiting enhanced decoloration and miner-alization, are also available. Considering the total mineralization of the com-pounds, the photocatalytic ozonation (UV/O3/TiO2) may show much lowerspecific energy consumption than the conventional photocatalysis (UV/TiO2)and ozonation (UV/H2O2/O3).106
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Hybrid Treatment Systems for Dye Wastewater 327
Fenton reagent (a mixture of H2O2 and Fe2+) and its modificationssuch as the thermal Fenton process201 or the photo-Fenton reaction usingFe(II)/Fe(III) oxalate ion, H2O2, and UV light have received great attentionas means for decolorization of synthetic dyes.190,202 In the case of the photo-Fenton technique, H2O2 is utilized more rapidly by three simultaneous reac-tions, namely, direct Fenton action, photoreduction of Fe(III) ions to Fe(II),and H2O2 photolysis. Thus this process produces more hydroxyl radicals incomparison to the conventional Fenton method or to photolysis.20,73 Certainreports suggest that in case of similar removal performance, Fenton’s processmay be preferred to related advanced oxidation alternatives (e.g., UV/H2O2)in view of lower energy consumption, lower H2O2 consumption, lowersludge disposal cost (as compared to higher reagent cost), higher flexibility,and lower maintenance requirement.24 However, Fenton reagent necessitatesuse of a large amount of acidic and alkaline chemicals (ideal pH about 2.5).Compared to Fenton’s reagent, the β-FeOOH-catalyzed H2O2 oxidation pro-cess takes advantage of its applicability over a wider pH range between 4to 8, and moreover no sludge is produced.107 In order to take advantage ofthe oxidizing power of Fenton’s reagent yet eliminate the separation of ironsalts from the solution, the use of an “H2O2/iron powder” system has beenrecommended. Such process may yield better dye removal than “H2O2/Fe+2”due to the chemisorption on iron powder in addition to the usual Fenton-type reaction.203 Fenton-type reactions based on other transition metals (e.g.,copper), although less explored to date, have also been reported to be in-sensitive to pH and effective for degradation of synthetic dyes.211,212
Among the AOPs, the photo-Fenton reaction207 and the TiO2-mediatedheterogeneous photocatalytic treatment38processes are capable of absorbingnear-UV spectral region to initiate radical reactions. Their application wouldpractically eliminate major operating costs when solar radiation is employedinstead of artificial UV light. The ferrioxalate solution that has long beenbeing used as chemical actinometer may be used in photo-Fenton process toderive further benefit by replacing UV with solar radiation.7 Recently, severalattempts have been made to increase the photocatalytic efficiency of TiO2;these include noble metal deposition, ion doping, addition of inorganic co-adsorbent, coupling of catalysts, use of nanoporous films, and so on. Apartfrom that, new catalysts, such as polymeric metalloporphyrins, have beenreported to be easily excited by violet or visible light, whereas availableutilization of solar energy by commonly used TiO2 is only about 3%.38
2.2. Photochemical/Electrochemical
In electrochemical treatments, oxidation is achieved by means of elec-trodes where a determined difference of potential is applied. On thisprinciple, several different processes have been developed as cathodicand anodic processes: direct and indirect electrochemical oxidation,
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328 F. I. Hai et al.
electrocoagulation, electrodialysis, electromembrane processes, and electro-chemical ion exchange.40 Occasionally, combination of electrochemical tech-nology and photocatalysis has been adopted to yield some unique advan-tages. For instance, chemical synergism of photocatalysis and electrochemicalprocesses may yield enhanced decoloration and chemical oxygen demand(COD) removal,6 and added advantage may be derived from existence of saltin solution, which originally is detrimental for sole photocatalysis.238 Con-versely, the electro-Fenton process requires no addition of chemical otherthan a catalytic quantity of Fe+2, since H2O2 is produced in situ, therebyavoiding transport of this hazardous oxidant.76,154 In the pulsed high-voltageelectric discharge process, addition of oxidants such as H2O2 yields highlyreactive free radical species through photodissociation of H2O2 and therebyenhances the whole process.200
2.3. Sonolysis and other AOPs
Acoustic cavitation due to ultrasound vibration within a liquid generates localsites of high temperature and pressure for a short period of time, which givesrise to H2O sonolysis with production of radical species and direct or indirect(via free radicals) destruction of solute. However, stand-alone application ofsonolysis hardly results in complete mineralization of pollutant streams con-taining complex mixtures of organic and inorganic compounds.73 In viewof the substantial amount of energy employed in generating free radicals viaacoustic cavitation bubbles, efforts have been made to improve its efficiency.It has frequently been explored in association with other AOPs. For exam-ple, combined use of sono-photochemical process can prevent severe masstransfer limitation and reduced efficiency of photocatalyst owing to adsorp-tion of contaminants at the surface. On the other hand, such combinationcan alleviate the limitations of separate application of sonolysis.148,198 A sim-ilar advantage has been reported in case of concurrent sonolysis and MnO2
oxidation.68 Sonification has also been reported to bring about dramatic en-hancement in oxidation efficiency of UV/H2O2 by improving oxygen uptakeand transfer.63,64,216 Combined application of sonolysis and O3/UV facilitatesO3 diffusion and photolysis of ultrasound-generated H2O2.53,90,206 Such acombination hence yields large number of free radicals. Addition of FeSO4
in solution may result in Fenton reaction with H2O2 evolved from simultane-ous sonification and may achieve improved decoloration and TOC removalas compared to sonification only.93 Simultaneous sonolysis has also beenreported to enhance electro-oxidation of dye.135
3. COMBINATION: AOPs AND OTHERPHYSICOCHEMICAL PROCESSES
Many studies have focused on different combinations among physicochem-ical systems for treatment of textile and dye wastewaters. Combinations of
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Hybrid Treatment Systems for Dye Wastewater 329
conventional physicochemical techniques with the AOPs have as well ap-peared as an attractive option. Table 3 encapsulates information derived frombroad spectrum of typical studies dealing with such combinations.
3.1. Coagulation-Based Combinations
Coagulation/flocculation/precipitation processes have been used intensivelyfor decolorizing wastewater. For the pretreatment of raw wastewater beforedischarging to publicly owned treatment plants, these processes may be sat-isfactory with respect to COD reduction and partial decolorization. Theirstand-alone application in treating textile/dye waste is, however, relativelyineffective;79,101,163 for example, only 50% removal was achieved using eitheralum or ferrous sulfate for an azo reactive yellow dye.79 In the coagulationprocess, it is difficult to remove highly water-soluble dyes, and, even moreimportant, the process produces a large quantity of sludge.179
Nevertheless, researchers are persistent in their pursuit of minimizingthe limitations of this technology. For instance, polyaluminum ferric chlo-ride (PAFC), a new type of composite coagulant, was reported to have theadvantages of high stability and good coagulating effect for hydrophobic aswell as hydrophilic dyes. Its decoloration capacity surpassed that of polyalu-minum chloride and polyferric sulfate.66 On the other hand, to avoid massivesludge disposal problem, different novel approaches, such as coagulation oflow-volume segregated dye bath (rather than that of a colossal amount ofmixed wastewater),74 alum sludge recycling,41 coagulant recovery from tex-tile chemical sludge,122 reuse of textile sludge in building materials,16 andprocesses like vermicomposting of textile mill sludge67 and coagulation fol-lowed by activated carbon adsorption163 have been proposed. Coagulationfollowed by adsorption was reported to produce effluent of reuse standard,apart from cutting down the coagulant consumption by 50%, hence loweringthe volume of sludge formed, in comparison to coagulation only.163
Coagulation in combination with advanced oxidation processes, eitherin sequential or in concurrent manner, has been reported for dye wastewater.For example, simultaneous application of coagulation and Fenton oxidationhas revealed improved performance over their stand-alone applications.101
One of the limitations of the Fenton oxidation process is that large amountsof small, hard-to-settle flocs are consistently observed during the process.Chemical coagulation following Fenton treatment has been found to re-duce floc settling time, enhance decoloration, and reduce soluble iron ineffluent.131 Conversely, the photo-Fenton process subsequent to coagulationwas reported to complete decoloration and yield better COD removal, withthe added advantage of reducing load on the advanced oxidation process,thereby reducing chemical usage.18 Investigation on sequential use of co-agulation and ozonation revealed the superiority of the scheme involvingozonation preceded by coagulation over the reversed scheme.209 Multistage
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TAB
LE3
.Typ
ical
Exa
mple
sofCom
bin
atio
ns
Bet
wee
nConve
ntio
nal
Phys
icoch
emic
alPro
cess
esan
dA
OPs
Tech
nolo
gyD
ye/w
aste
wat
erD
etai
lsRef
eren
ce(y
ear)
Fento
n/c
hem
ical
coag
ula
tion
C.I
direc
tN=N
blu
e20
2,C.I
reac
tiveN
=Nbla
ck5;
PVA
81–8
6%CO
D(I
niti
ally
>10
00m
g/L)
rem
ova
l&
dec
olo
ratio
n(D
ye=
200
mg/
L)in
2h
with
[H2O
2]/
[FeS
O4]=
1000
/400
atpH
=3,
while
subse
quen
tco
agula
tion
atpH
=7–
10w
ith10
0m
g/L
PAC
&2m
g/L
poly
mer
reduce
dfloc
settlin
gtim
e,en
han
ced
dec
olo
ratio
nan
dre
duce
dso
luble
Fein
effluen
t.
131
(199
7)
Fento
n+
chem
ical
coag
ula
tion
Dis
per
se-B
lueN
=N10
6,Yel
low
AQ
54;Rea
ctiv
e-B
lueA
Q49
,Yel
low
N=N
84
Coag
ula
tion
(pH
=5–
7):Rem
ova
lper
molFe
+3[C
OD
,D
YE]:
Dis
per
se(0
.74–
0.93
mM
FeCl 3
)=
[460
.2–4
77g,
525.
7–67
2.7]
;Rea
ctiv
e(1
.85–
2.78
mM
FeCl 3
)=
[37.
4–86
.5g,
109.
5–19
2.7
g].Fe
nto
n(p
H=
3;30
min
;[F
e+2]:
[H2O
2]=
1:0.
2–1:
0.37
):Rem
ova
lper
molFe
+2[C
OD
,D
YE]:
Dis
per
se=
[14–
80g,
3.7–
20.8
g];Rea
ctiv
e=
[114
.2–1
99.6
g,11
8.9–
489.
2g].
Com
bin
ed:B
oth
dye
s,90
%CO
D&
99%
dye
rem
ova
l.
101
(200
4)
O3/c
oag
ula
tion
Azo
dye
man
ufa
cturing
was
tew
ater
(subje
cted
toch
lorinat
ion)
Rem
ova
l:A
fter
Ozo
nat
ion
[70
min
;56
mg
O3
/min
;1.
6L/
min
;pH
=10
.3]CO
D=
25%
,Colo
r=
43%
..A
fter
subse
quen
tCa(
OH
) 2co
agula
tion
[787
mg/
L,pH
=12
]CO
D=
50%
,TO
C=
42%
,Colo
r=
62%
.;ef
fect
ive
rem
ova
lofch
loro
org
anic
saf
ter
two
stag
es.
186
(199
8)
Coag
ula
tion/O
3Te
xtile
was
tew
ater
Coag
ula
tion
[Al 2
(SO
4) 3
,60
ppm
;poly
elec
troly
te0.
6ppm
]re
sulte
din
65–7
5%&
20%
reduct
ion
ofCO
D&
abso
rban
ce(initi
alCO
D=
890
mg/
L),w
hile
subse
quen
tozo
nat
ion
(3m
g/m
in,10
–15
min
)ga
vea
further
90%
&20
–25%
reduct
ion
ofre
sidual
colo
r&
CO
D.O
zonat
ion
pre
ceded
by
coag
ula
tion
gave
wors
ere
sult.
209
(199
4)
Multi
stag
e(c
oag
ula
tion/O
3)
Dye
man
ufa
cturing
was
tew
ater
Singl
est
age
coag
ula
tion
(2.5
%,v/
v,Fe
Cl 2
;35
mg/
Lpoly
mer
;pH
=8.
5)fo
llow
edby
ozo
nat
ion
(pH
=11
;90
min
)ac
hie
ved
[19%
CO
D,88
%co
lor]
and
[67%
CO
D,99
.3%
colo
r]re
mova
l,re
spec
tivel
y(initi
alCO
D=
7700
mg/
L;Colo
r=
6700
0A
DM
I).Thre
etim
esre
pet
ition
ofth
ese
quen
cew
hile
keep
ing
tota
lozo
nat
ion
time
sam
e(3
at30
min
)ac
hie
ved
>90
%CO
D&
99.9
9%co
lor
rem
ova
l,th
esu
per
iority
of
multi
stag
etrea
tmen
tbei
ng
less
convi
nci
ng
for
was
tew
ater
with
sim
ple
rco
mposi
tion.
86(1
998)
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Coag
ula
tion/U
V-
Fento
nIn
tegr
ated
pla
ntco
nta
inin
gva
riet
yofpro
cess
esra
ngi
ng
from
des
izin
gto
dye
ing
and
ulti
mat
efinis
hin
g
UV
(20
W)/
TiO
2(1
g/L)
/H2O
2(1
0m
M)/
Fe+2
(1
mM
)trea
tmen
t(p
H=
4)fo
llow
ing
coag
ula
tion
trea
tmen
tac
hie
ved
com
ple
tedec
olo
ratio
n(3
0m
in)
&a
max
imal
48%
(ove
rth
atac
hie
ved
by
coag
ula
tion)
CO
Dre
mova
l(1
h),
the
CO
Dofra
w,co
agula
ted,an
doxi
diz
edsa
mple
bei
ng
1063
,55
6,&
269
mg/
L,re
spec
tivel
y.
18(2
003)
Coag
ula
tion/c
arbon
adso
rptio
nC.I
reac
tiveN
=Nre
d45
,C.I
reac
tiveN
=Ngr
een
8Rem
ova
l(D
ye=
1g/L
):A
fter
AlC
l 3·6H
2O
coag
ula
tion
[0.8
g/L;
pH
=3.
5]:RR
45[Colo
r98
.8%
,TO
C98
.1%
,CO
D93
.4%
];RG
8[C
olo
r99
%,
TO
C96
.9%
,CO
D83
.8%
].A
fter
carb
on
adso
rptio
n[0
.24
&0.
84g/
L;2
hr]:RR
45[C
olo
r99
.9%
,TO
C99
.7%
,CO
D95
.7%
];RG
8[Colo
r99
.9%
,TO
C99
.2%
,CO
D91
.3%
].H
alfth
eco
agula
ntco
nsu
mptio
nan
dlo
wer
volu
me
ofsl
udge
form
atio
nin
com
par
ison
todye
rem
ova
lby
coag
ula
tion
only
.
163
(200
4)
Photo
cata
lysi
s/ad
sorp
tion
(pow
der
edac
tivat
edca
rbon,PA
C)
Hum
icac
id(n
atura
lco
loring
mat
ter)
3–4
hirra
dia
tion
induce
ddec
reas
ein
UV
280,
UV
254,
TO
Can
dCO
Dan
dsi
multa
neo
us
impro
vem
entofbio
deg
radab
ility
with
no
sign
ifica
nt
dec
reas
ein
adso
rptiv
ityofsu
bse
quen
tPA
C.
22(1
996)
Solv
entex
trac
tion
(&dye
reco
very
)/Fe
nto
nre
agen
t
1-D
iazo
-2-n
aphth
ol-4-
sulfonic
acid
(aci
ddye
inte
rmed
iate
)
82%
Ext
ract
ion
usi
ng
solv
ent(t
rial
kyla
min
eN
235)
and
subse
quen
tdye
reco
very
by
strippin
gle
dto
95%
dec
olo
ratio
nofth
eorigi
nal
effluen
t.Su
bse
quen
tra
ffinat
etrea
tmen
t(a
fter
lime
neu
tral
izat
ion)
by
Fento
nre
agen
tac
hie
ved
achro
mat
icef
fluen
tw
ithCO
D<
100
mg/
L.
87(2
004)
O3/i
on
exch
ange
Cu-c
om
ple
xD
irec
tN=N
Blu
e80
Concu
rren
tdec
olo
ratio
n&
met
alre
leas
eby
0.2
mg
O3/m
gdye
and
subse
quen
tm
etal
rem
ova
lby
stro
ng
acid
catio
n-e
xchan
gere
sin
atpH
=2
achie
ved
Cu
conce
ntrat
ion
bel
ow
det
ecta
ble
limits
inth
eef
fluen
t.
97(1
996)
Adso
rptio
n(fl
uid
ized
GA
C)
+O3
Aci
dblu
e9,
Mord
antN
=N
bla
ck11
,Rea
ctiv
eAQ
blu
e19
,Rea
ctiv
eN=N
ora
nge
16
Influen
t:pH
=5.
1–9.
2,CO
D=
250–
1800
mg/
1,SS
=45
–320
mg/
,tu
rbid
ity(N
TU
)=
50–2
10.Com
bin
edozo
nat
ion
and
GA
Cad
sorp
tion
(4L
O3/m
inper
100
gmG
AC)
offer
sm
utu
alen
han
cem
entnam
ely
rege
ner
atio
nofG
AC
&ca
taly
sis
ofO
3.
132
(200
0)
(Con
tin
ued
on
nex
tpa
ge)
331
Dow
nloa
ded
by [
Kan
sas
Stat
e U
nive
rsity
Lib
rari
es]
at 0
5:45
01
Dec
embe
r 20
13
TAB
LE3
.Typ
ical
Exa
mple
sofCom
bin
atio
ns
Bet
wee
nConve
ntio
nal
Phys
icoch
emic
alPro
cess
esan
dA
OPs
(Con
tin
ued
)
Tech
nolo
gyD
ye/w
aste
wat
erD
etai
lsRef
eren
ce(y
ear)
Adso
rptio
n(G
AC)
+UV
/H2O
2
Rea
ctiv
eEve
rzolB
lack
–GSP
Sim
ulta
neo
us
adso
rptio
n(8
g/L)
&U
V–
H2O
2oxi
dat
ion
(0.0
09M
)ac
hie
ved
syner
gist
icdec
olo
ratio
n&
TO
Cre
mova
l(c
om
ple
te&
50%
,30
min
)fo
rth
eorigi
nal
lypoorly
adso
rbab
ledye
(36
ppm
)co
ncu
rren
tw
ithco
stsa
ving
due
tore
use
ofad
sorb
ent.
91(2
002)
Adso
rptio
n(β
-Fe
OO
H)/
oxi
dat
ive
(H2O
2)
rege
ner
atio
n
C.I.Rea
ctiv
eN=N
Red
198
Adso
rptio
nonto
gran
ula
ted
β-F
eOO
H(1
70m
g/g)
and
itsre
pea
ted
reuse
(6cy
cles
)fo
llow
ing
rege
ner
atio
nby
cata
lytic
oxi
dat
ion
usi
ng
H2O
2(7
mg
dye
/mg;
6h
at24
.5m
l/m
in);
sele
ctiv
ead
sorp
tion/o
xidat
ion,lo
wer
oxi
dan
tdose
and
no
conve
ntio
nal
conce
ntrat
etrea
tmen
t.Si
multa
neo
us
trea
tmen
tre
com
men
ded
for
hig
hsa
lt-co
nta
inin
gw
aste
wat
er.
107
(200
2)
Ion-e
xchan
ger
(quar
tern
ized
amm
oniu
mce
llulo
se)
/chem
ical
reduct
ion
(bis
ulfi
te-m
edia
ted
boro
hyd
ride)
Ora
nge
II(A
cid
N=N
Ora
nge
7),Rea
ctiv
eN=N
red
180
Anio
nex
chan
ger
bound
383
mg/
gofO
range
II&
272
mg/
gofre
activ
edye
while
subse
quen
tK
BH
4/N
aHSO
3(2
mM
/10
mM
)re
duct
ion
of
dye
(1m
Mso
lutio
n)
follo
wed
by
salt
or
bas
eex
trac
tion
resu
lted
inal
most
com
ple
tere
gener
atio
nofth
eco
stly
ion
exch
ange
r,es
tablis
hin
ga
feas
ible
pro
cess
couplin
gtw
ote
chnolo
gies
with
limite
dpote
ntia
lal
one.
117
(199
7)
Adso
rptio
n(P
AC)/
wet
air
oxi
dat
ion
(WA
O)
Chem
ictiv
eB
rill.
Blu
eR
(Rea
ctiv
eAQ);
Cib
acorn
Turq
uois
eB
lue
G(R
eact
iveT
C)
Effi
cien
ttrea
tmen
toflo
wer
conce
ntrat
ions
ofunhyd
roliz
edre
activ
edye
sby
firs
tad
sorb
ing
on
PAC,an
dsu
bse
quen
tly,re
gener
atin
g(>
98%
afte
rco
nse
cutiv
e4
cycl
esw
ithonly
8%to
talw
eigh
tlo
ss)
spen
tPA
Cby
WA
O(1
50–2
50◦ C
,O
2par
tialpre
ssure
0.69
–1.3
8M
pa)
,an
dre
cycl
ing
the
rege
ner
ated
carb
on.
191
(200
2)
Adso
rptio
n(C
uFe
2O
4)/
cata
lytic
com
bust
ion
Aci
dN
=NRed
BD
ye,pre
conce
ntrat
edon
adso
rben
t/ca
taly
stCuFe
2O
4(>
95%
rem
ova
lfr
om
100
mg/
L;pH
<5.
5,dose
=0.
1g/
50m
l),af
ter
mag
net
icso
lid/l
iquid
separ
atio
n,w
assu
bje
ctto
com
ple
teco
mbust
ion
atre
lativ
ely
low
tem
p(3
00◦ C
)w
ithoutev
olu
tion
ofhar
mfu
lpro
duct
s;an
din
the
pro
cess
,CuFe
2O
4w
asre
gener
ated
allo
win
gef
fici
entre
use
ove
rex
tended
cycl
es.
223
(200
4)
332
Dow
nloa
ded
by [
Kan
sas
Stat
e U
nive
rsity
Lib
rari
es]
at 0
5:45
01
Dec
embe
r 20
13
Adso
rptio
n(f
erro
us
modifi
edG
AC)
+m
icro
wav
e(M
W)
induce
dO
xidat
ion
Arg
azolB
lue
BF-
BR
150%
(bifunct
ional
N=N
reac
tive
dye
)
98.3
%dec
olo
ratio
nan
d96
.8%
CO
Dre
mova
lw
asac
hie
ved
when
dye
solu
tion
(50
ml,
300
mg/
L)co
nta
inin
gfe
rrous
modifi
edG
AC
(2g)
was
subje
ctto
MW
irra
dia
tion
(5m
in,50
0W,24
50M
Hz)
,th
ere
mova
lm
echan
ism
invo
lvin
gG
AC
adso
rptio
n&
subse
quen
tco
mbust
ion
(induce
dby
MW
)on
itssu
rfac
e.N
eglig
ible
strippin
gofFe
+2fr
om
GA
Csu
rfac
eunder
reuse
for
man
ytim
es.
166
(200
4)
Adso
rptio
n(G
AC)/
mic
row
ave
(MW
)re
gener
atio
n
C.I
Aci
dN
=NO
range
7D
ye(5
00m
g/L)
-ex
hau
sted
GA
Cco
uld
be
succ
essf
ully
rege
ner
ated
by
mic
row
ave
irra
dia
tion
(245
0M
Hz,
850
W,5
min
)fo
rre
pea
ted
cycl
esin
volv
ing
low
GA
Clo
ss(6
.5%
,4
cycl
es)
and
adso
rptio
nra
teev
enhig
her
than
that
ofvi
rgin
GA
Cdue
topore
-siz
edis
trib
utio
n&
surf
ace
chem
istry
modifi
catio
n.
176
(200
4)
Sonic
atio
n/F
e0
reduct
ion
C.I
Aci
dN
=NO
range
7Puls
edso
nic
atio
n(2
0kH
z,25
0W
),by
impro
ving
mas
stran
sfer
&al
soin
crea
sing
activ
esi
tes
on
Fe-s
urf
ace,
dra
mat
ical
lyen
han
ced
dye
(50
mg/
L)dec
olo
ratio
nef
fici
ency
ofm
ildre
duci
ng
agen
tFe
0(1
g/L,
pH
=3)
,th
eco
mbin
edpro
cess
achie
ving
91%
dye
rem
ova
lin
30m
info
llow
ing
1stord
erki
net
ics.
237
(200
5)
Mem
bra
ne
bas
edozo
nat
or
Blu
e19
reac
tive
dye
;U
ntrea
ted
exhau
sted
dye
-bat
h
Thin
coat
ing
ofTiO
2&
γ-A
l 2O
3on
cera
mic
mem
bra
ne
(ZrO
2,α-A
l 2O
3)
elim
inat
eddef
ects
&hen
ceal
low
edoper
atio
nat
hig
hga
spre
ssure
with
subst
antia
lozo
ne
tran
sfer
impro
vem
ent,
even
tual
lyyi
eldin
g10
0%&
62%
dec
olo
ratio
nofpure
dye
(0.0
72m
mol/
L)&
untrea
ted
dye
bat
h,re
spec
tivel
y,in
2h
45(2
003)
Photo
cata
lytic
mem
bra
ne
reac
tor
Congo
red
N=N
,Pat
ent
blu
eN=N
The
contin
uous
photo
cata
lytic
mem
bra
ne
(NF;
30–7
0L/
m2h)
reac
tor
with
susp
ended
TiO
2(1
g/L)
&im
mer
sed
UV
lam
p(1
25W
)outp
erfo
rmed
itsco
unte
rpar
tw
ithTiO
2en
trap
ped
on
mem
bra
ne
and
irra
dia
ted
with
exte
rnal
lam
p(5
00W
),ac
hie
ving
alm
ost
com
ple
tephoto
deg
radat
ion
ofdye
s(5
00m
g/L)
with
hig
her
rate
.
145
(200
4)
(Con
tin
ued
on
nex
tpa
ge)
333
Dow
nloa
ded
by [
Kan
sas
Stat
e U
nive
rsity
Lib
rari
es]
at 0
5:45
01
Dec
embe
r 20
13
TAB
LE3
.Typ
ical
Exa
mple
sofCom
bin
atio
ns
Bet
wee
nConve
ntio
nal
Phys
icoch
emic
alPro
cess
esan
dA
OPs
(Con
tin
ued
)
Tech
nolo
gyD
ye/w
aste
wat
erD
etai
lsRef
eren
ce(y
ear)
Mem
bra
ne/
wet
air
oxi
dat
ion,W
AO
Dis
per
seN
=Nblu
eCI
79N
Fm
embra
ne
achie
ved
>99
%co
lor
and
97%
CO
Dre
ject
ion
ofdye
com
pound
while
the
hom
oge
neo
us
copper
sulfat
eca
taly
zed
WA
O(1
60◦ –
225◦ C
,O
2par
tialpre
ssure
0.69
–1.3
8M
pa)
reduce
d90
%CO
Dfr
om
conce
ntrat
e(1
20m
in).
55(2
000)
Mem
bra
ne/
wet
air
oxi
dat
ion,W
AO
Dye
ing
was
tew
ater
conta
inin
gRea
ctiv
eblu
e,In
dig
o,Su
lfur
bla
ck&
oth
erpro
cess
chem
ical
s
Rep
laci
ng
O2
with
stro
nge
roxi
dan
tH
2O
2(5
0%ofst
oic
hio
met
ric
amount)
&ad
din
gCu-A
Cca
taly
st(2
g/L)
,80
%TO
C&
90%
colo
rw
asre
move
dfr
om
mem
bra
ne
conce
ntrat
eby
WO
under
mild
conditi
on
(110
◦ C,T
ota
lP
=50
kPa)
in30
min
118
(199
8)
Mem
bra
ne/
sonic
atio
n/
WA
ORea
ctiv
eTC
Turq
uois
eblu
eCI2
5N
Fm
embra
ne
(1.5
Mpa;
flux
=0.
084
m/h
)re
move
d90
.3%
CO
D&
98.7
%co
lor
from
pu
red
ye
solu
tion
(CO
D=
1500
mg/
L),w
hile
WO
(190
◦ C,O
2pre
ssure
=0.
69M
pa;
pH
=7)
reduce
d90
%CO
Dfr
om
dilu
ted
(CO
D=
500–
700
mg/
L)co
nce
ntrat
e(1
20m
in).
Sonic
atio
n(1
50/3
50W
,av
g./p
eak;
40kH
z;30
min
)w
ases
sentia
lto
mak
em
embra
ne
rete
nta
tefr
om
act
ua
lw
ast
ewa
ter
tobe
amen
able
tosu
bse
quen
tW
O.
54(1
999)
Mem
bra
ne/
O3
Rea
ctiv
e(R
emaz
olblu
eB
B,
Intrac
orn
gold
enye
llow
VS-
GA
,Rem
azolre
dRB
)&
salt
NF
mem
bra
ne
(9.4
1L/m
in;Re
=83
8)ge
ner
ated
reusa
ble
per
mea
te(8
5%oforigi
nal
volu
me)
with
>99
%ofco
lor
&Cu,an
donly
15%
ofsa
ltre
mova
lw
hile
subse
quen
tozo
nat
ion
(7.7
3m
g/L.
min
,pH
=11
)re
move
dco
lor
from
the
conce
ntrat
efo
llow
ing
1stord
erki
net
ics,
the
rate
dec
reas
ing
with
incr
easi
ng
initi
aldye
colo
r.
222
(199
8)
UV-F
ento
n/c
oag
ula
tion
/mem
bra
ne
Rea
ctiv
eN=N
(Pro
cion
Red
HE7B
)Com
ple
teco
lor
rem
ova
l(D
ye=
50m
g/L)
and
79%
TO
Cre
mova
lw
ithin
20m
inby
photo
-Fen
ton
(pH
=3;
[H2O
2]/
[Fe+2
]=
20:1
;4
at15
WU
Vla
mp).
How
ever
9tim
esin
crea
sein
dis
solv
edso
lids
war
rants
subse
quen
tco
agula
tion/m
embra
ne
syst
emfo
rre
use
indye
/rin
sepro
cess
.
88(1
999)
334
Dow
nloa
ded
by [
Kan
sas
Stat
e U
nive
rsity
Lib
rari
es]
at 0
5:45
01
Dec
embe
r 20
13
Phys
icoch
emic
al/
mem
bra
ne
(UF/
NF)
Synth
etic
text
ilem
anufa
cturing
was
tew
ater
Raw
wat
er:Conduct
ivity
(mS/
cm)
2.06
;S.
S.(m
g/L)
82.6
;CO
D(m
g/L)
1640
;Turb
idity
(NTU
)15
.65;
Inord
erto
reuse
the
wat
erin
rinse
pro
cess
es,it
isnec
essa
rya
neg
ligib
leCO
Dan
da
conduct
ivity
low
erth
an1
mS/
cm.Phys
icoch
emic
al(p
H=
8.5,
CD
K−F
ER20
=20
0m
g/L,
Cnal
co,fl
occ
ula
nt=
1m
g/L)
:50
%CO
Dre
mova
l;N
Fm
embra
ne
(flow
rate
=40
0L/
h,TM
P=
1M
Pa)
:10
0%CO
Dre
mova
l,85
%co
nduct
ivity
rete
ntio
n.[R
eusa
ble
]
25(2
002)
Phys
icoch
emic
al/
mem
bra
ne
(N
F)Te
xtile
was
tew
ater
Raw
wat
er:Conduct
ivity
(mS/
cm)
4.53
;CO
D(m
g/L)
1630
.Phys
icoch
emic
al(p
H=
12,Fe
+2=
700
mg/
L):72
.5%
CO
Dre
mova
l;N
Fm
embra
ne
(flow
rate
=20
0L/
h,TM
P=
20bar
,flux
=8–
10L/
m2h):
CO
D<
100
mg/
L;Conduct
ivity
<1
mS/
cm
26(2
003)
Cla
riflocc
ula
tion/
ozo
na-
tion/m
embra
ne
(UF)
Was
tew
ater
from
carb
oniz
ing
pro
cess
,fr
om
dye
ing
and
fulli
ng
49%
turb
idity
&71
%co
lor
rem
ova
lby
clar
iflocc
ula
tion
&ozo
nat
ion,
resp
ectiv
ely,
and
hig
htu
rbid
ity(2
7%)
&TSS
(30%
)re
mova
lby
the
subse
quen
tU
Fm
embra
ne
contrib
ute
dto
achie
vem
entoffinal
66%
CO
Dan
d93
%co
lor
rem
ova
l,m
akin
gre
use
,af
ter
50%
dilu
tion
with
wel
lw
ater
,poss
ible
.
139
(200
2)
Act
ivat
edC/m
embra
ne
(NF/
RO
)Rea
ctiv
edye
for
cotton
Hotw
ater
reuse
inrinsi
ng
afte
rre
clam
atio
nby
mem
bra
ne
(deg
radat
ion
offiltr
atio
nre
man
ence
inan
aero
bic
dig
este
rs);
and
reuse
ofdye
bat
hw
ater
and
salts
afte
rad
sorp
tion
ofdye
stuff
and
CO
Don
activ
ated
carb
on.
219
(199
6)
Mem
bra
ne
(UF)
/adso
rptio
n(a
ctiv
ated
carb
on
cloth
,A
CC)
Aci
dN
=NO
range
II,A
cid
N=N
Brilli
antYel
low
(colo
r)&
Ben
tonite
(turb
idity
)
Both
pro
cess
are
com
ple
men
tary
inth
atco
mpounds
too
larg
eto
be
adso
rbed
onto
ACC
are
succ
essf
ully
reta
ined
by
the
mem
bra
ne
(>98
%tu
rbid
ity&
15–4
0%dye
rem
ova
l),w
hile
low
-mole
cula
r-w
eigh
torg
anic
sar
ew
ellad
sorb
edby
the
ACC
(38–
180
mg/
g,dye
-spec
ific)
.Rep
laci
ng
UF
with
NF,
or
UF
mem
bra
ne
wra
pped
up
ina
ple
ated
ACC
reco
mm
ended
toav
oid
early
bre
akth
rough
ofA
CC.
168
(200
0)
Note
.D
iffe
rentdye
chro
mophore
s:N
=N: A
zo,
AQ
:Anth
raquin
one,
TC:Phth
alocy
anin
e.
335
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336 F. I. Hai et al.
application of coagulation followed by ozonation was proved to be superiorto their single-pass sequential application (total ozonation time the same).86
The advantage of the multistage application was more convincing in the caseof wastewater with more recalcitrant composition.
3.2. Adsorption-Based Combinations
Adsorption techniques, specially the excellent adsorption properties ofcarbon-based supports, have been utilized for the decolorization of dyesin the industrial effluents.60 Activated carbon, either in powder or granularform, is the most widely used adsorbent for this purpose because of its ex-tended surface area, microporous structure, high adsorption capacity, andhigh degree of surface reactivity.137 It is very effective for adsorbing cationic,mordant, and acid dyes and to a slightly lesser extent dispersed, direct, vat,pigment, and reactive dyes.179 However, the use of carbon adsorption fordecolorization of raw wastewater is impractical because of competition be-tween colored molecules and other organic/inorganic compounds. Hence itsuse has been recommended as a polishing step or as an emergency unit at theend of treatment stage to meet the discharge color standards.79 The fact thatactivated carbon is expensive and weight loss is inevitable during its costlyon-site regeneration (10% loss in the thermal regeneration process)99 impedesits widespread use. Utilization of nonconventional, economical sources (in-dustrial or agricultural by-products) rather than usual relatively expensivematerials (coconut shell, wood or coal) as precursors for activated carbonhas been proposed to achieve cost-effectiveness in its application.142,181
There has been considerable interest in using low-cost adsorbents fordecolorization of wastewater. These materials include chitosan, zeolite, andclay; certain waste products from industrial operations such as fly ash, coal,and oxides; agricultural wastes and lignocellusic wastes; and so on.14,151 Eachof the non-regenerable economical adsorbents has its specific drawbacks andadvantages; all, however, pose further disposal problem. To do away withthe disposal problem, easily regenerable adsorbent is required.99
As mentioned earlier, adsorption is a nondestructive method involvingonly phase change of pollutants, and hence imposes further problem in theform of sludge disposal. The high cost of adsorbent also necessitates its re-generation. Conversely, some catalytic oxidation/reduction systems appearto be more efficient when treating small volumes of concentrated dyes. So itappears attractive to combine adsorption with some other process in a systemwhere contaminants are preconcentrated on adsorbent and then separatedfrom water. The contaminants thus separated may subsequently be mineral-ized, for example, by wet air oxidation,191,223 or degraded to some extent, forinstance, with azo bond reduction by bisulfite-mediated borohydride117 soas to regenerate the adsorbent and reuse. In this way an economical processcoupling two treatment technologies eliminating their inherent drawbacks
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Hybrid Treatment Systems for Dye Wastewater 337
may be developed. If partial degradation is applied to regenerate the adsor-bent, it will still leave behind a small volume of wastewater (as comparedto the volume that existed before adsorption) to be treated. This again canbe conveniently taken care of by applying some AOP. Ince et al.89proposeda slightly modified version of the aforementioned so-called “phase-transferoxidation.” Their strategy was comprised of simultaneous operation of ad-sorption and AOP followed by periodic on-site destructive regeneration ofthe spent adsorbent. Adsorption concurrent with ozonation,132 UV–H2O2,91
or microwave-induced oxidation132 has been reported to yield mutual en-hancements like catalysis of AOP by adsorbent and simultaneous regenera-tion of adsorbent. A rather elaborate method involving solvent extraction andcatalytic oxidation has been documented in the literature.87,150 The methodconsists of dye extraction using an economical solvent followed by dye re-covery through chemical stripping. In this way the solvent is also regener-ated. Finally, treatment of the extraction raffinate can be achieved by catalyticoxidation.
3.3. Membrane-Based Combinations
Membrane separation endows the options of either concentrating thedyestuffs and auxiliaries and producing purified water,208 or removing thedyestuff and allowing reuse of water along with auxiliary chemicals,110,172,174
or even realizing recovery of considerable portion of dye, auxiliaries, andwater all together.171 Such recovery/reuse practice reduces many-fold therecurring cost for the treatment of waste streams. The fact that the dyeingbehavior of the residual dye should ideally be identical to that of the fresh dyemay restrict dye recovery and reuse to specific dye classes.35,65 Accordingly,water and/or electrolyte recovery from dye bath effluent has become the fo-cus of the contemporary literature. However, concentrated sludge productionand occurrence of frequent membrane fouling requiring costly membrane re-placement impede widespread use of this technology.36 Two distinct trendsare hence notable among the reported studies that couple membrane sepa-ration with other technologies. Some studies mainly focus on alleviation ofthe membrane-concentrate disposal problem, while others seek to offer com-plete hybrid systems wherein elimination of the limitations of the membranetechnology (e.g., fouling) and/or those of the counterpart technologies (e.g.,ultrafine catalyst separation in photocatalysis) may be expected.
Hybrid processes based on membrane and photocatalysis have beenreported to eradicate the problem of ultrafine catalyst to be separated fromthe treated liquid in case of slurry reactors, with the added advantage ofmembrane acting as selective barrier for the species to be degraded. Onthe other hand, in case of immobilized catalysis, membrane may play therole of support for the photocatalyst.145 For coupling with photocatalysis,membrane distillation, however, has been reported to be more beneficial in
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338 F. I. Hai et al.
comparison with pressure-driven membrane process, as significant foulingmay be associated with the latter. Tay et al.204 proposed a photo-oxidative(UV/TiO2/H2O2) pretreatment prior to membrane filtration to partially breakdown the high-molecular-weight compounds that cause membrane fouling.The relatively smaller fragments produced therefrom were still retainable bymembrane, and ,unlike the parent compounds, they did not affect the chargeof the membrane surface.
Membrane contactors, involving mass transfer in the pores by diffusion(avoiding gas dispersion as macroscopic bubbles as in traditional ozonationsystems), offer the advantages of higher contact surface (equal to membranesurface, which may reach up to 30 km2/m3 H2O for hollow-fiber membranes),easy scale-up, no foam formation, and lower process cost (no requirementof ozone destruction, lower ozone loss).42,45
Numerous studies have reported on application of membrane filtration(ultrafiltration/nanofiltration, UF/NF) following coagulation/flocculation toproduce reusable water.25,26,139 Such application has the added advantageof minimizing membrane fouling. In this context, the hybrid coagulation-membrane reactor may offer another viable option. This treatment schememay also be placed subsequent to advanced oxidation processes in order toremove soluble degradation products.88
Application of separate technologies for segregated streams has beenrecommended by different researchers. For instance, Wenzel et al.219 recom-mended hot water reuse in rinsing after reclamation by membrane, and reuseof dye bath water and salts after adsorption of dyestuff and COD on activatedcarbon. Conversely, the hybrid adsorption-membrane reactor, offering syn-ergism in that the compounds too large to be adsorbed onto adsorbent aresuccessfully retained by the membrane while low-molecular-weight organicsare well adsorbed on adsorbent, is also worth mentioning.168
A considerable number of studies have been devoted to eradicationof the major drawback associated with membrane separation, that is, con-centrated residue remaining for disposal. As mentioned earlier, dyes in theconcentrate from the membrane separation unit, because of the usual qualityrequirements for the color shades in the dyed products, cannot be reused andmust be treated before discharge. In this respect, catalyzed wet air oxidation(WAO) has emerged as an efficient system.55,118 Sonification was found es-sential to make the membraneretentate from actual wastewater be amenableto subsequent WAO.54 On the other hand, augmentation of advanced oxida-tion process (e.g., ozonation) subsequent to membrane filtration has beenenvisaged as a scheme yielding several advantages, such as reducing wastevolume for oxidation while simultaneously recovering salt, and, in addition,limiting concentrated waste for disposal.222 A novel membrane-based inte-grated water management system for the exhausted dye bath and rinsingbath was proposed by Bruggen et al.34 The proposed scheme involved,in order of application, microfiltration membrane (pretreatment), loose
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Hybrid Treatment Systems for Dye Wastewater 339
nanofiltration membrane (NF-1, for organics removal), and another tighterNF membrane (NF-2, salt retention). According to that scheme, further sep-aration of organic fraction may be achieved by membrane distillation units,while retained salt may be recovered through membrane crystallization. Fi-nally, the organic sludge of high calorific value from the membrane distillationunit may be incinerated.
4. BIOLOGICAL TREATMENT-BASED COMBINATIONS
4.1. Combination Among Biological Processes
Conventionally a chemical coagulation step, preceded by229 or antecedentto57 biological treatment, is applied for dye wastewater. Combined treat-ment with municipal wastewaters is usually favored75 wherever applicable.Various biological treatment processes including activated sludge, fluidizedbiofilm,229 different fixed film systems,3 or combinations thereof230 have beenemployed. Although in case of aerobic bacteria cometabolic reductive cleav-age of azo dyes as well as utilization of azo compounds as sole source ofcarbon and energy (leading to mineralization) have been reported, dyes aregenerally very resistant to degradation under aerobic conditions.19,199 Toxic-ity of dye wastewater and factors inhibiting permeation of the dye throughthe microbial cell membrane reduce the effectiveness of biological degrada-tion. Dyestuff removal, hence, currently occurs in the primary settling tankof a wastewater treatment plant for the water-insoluble dye classes (disperse,vat, sulfur, azoic dyes), while the main removal mechanism for the water-soluble basic and direct dyes in conventional aerobic systems is adsorptionto the biological sludge. Reactive and acid dyes, however, adsorb very poorlyto sludge and are thus major troublemakers in relation to residual color indischarged effluents.160
Since reduction of the azo bond can be achieved under the reducingconditions prevailing in anaerobic bioreactors31 and the resulting colorlessaromatic amines may be mineralized under aerobic conditions,32 a combinedanaerobic-aerobic azo dye treatment system appears to be attractive. Trialswith various combinations, including simultaneous anaerobic/aerobic pro-cess (microbial immobilization on a matrix providing oxygen gradient113
or an anaerobic–aerobic hybrid reactor95), anoxic plus anaerobic/aerobicprocess,162 anaerobic/oxic system,5 and aerobic (cell growth)/anaerobic (de-colorization) system,37 have all been explored, involving fed batch, sequenc-ing batch, or continuous feeding strategies, with encouraging results.Bothcytoplasmic184 and membrane-bound114 unspecific azo-reductase activitiesunder anaerobic condition have been reported. Glucose, raw municipalwastewater, and yeast extract, among others, have been reported as examplesof an essential cosubstrate needed to obtain good anaerobic color removal.52
Different abiotic processes involving derivatives generated during bacterial
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340 F. I. Hai et al.
metabolism (e.g., sulfide, amino acid cysteine, ascorbate) may contribute indecolorization under anaerobic conditions.227 The biotic process, however,dominates in high-rate anaerobic bioreactors.233 Addition of redox-mediatingcompounds like anthraquinone sulfonate or anthraquinone disulfonate hasbeen reported to greatly enhance both the biotic and abiotic processes.233
However, during posttreatment of anaerobically treated azo dye-containingwastewater, there will be competition between biodegradation and autoxi-dation of aromatic amines. This may be problematic not only because theformed products are colored but also because some of these compounds,such as azoxy compounds, may cause toxicity.232 It should be emphasizedthat in high-nitrogen waste waters it makes little sense to remove part ofCOD by anaerobic treatment in the first step when COD has to be addedagain to the effluent afterward in order to achieve nitrogen removal.52
Biological treatment is a cost-competitive and eco-friendly alternative.Researchers are hence persistent in their pursuit of minimizing the inher-ent limitations of biological dye wastewater treatments. Several innovativeattempts to achieve improved reactor design and/or to utilize special dye-degrading microbes or to integrate textile production with wastewater treat-ment have been documented in literature. Some of these innovative en-deavors include a two-stage activated sludge process (high-load first stage,achieving biosorption and incipient decomposition of high-molecular-weightorganic compounds, followed by a low-load polishing stage);104 high-rateanaerobic systems uncoupling hydraulic retention time from solids reten-tion time;125 two-phase anaerobic treatment wherein the acidic-phase biore-actor is also shared for textile production (integration of production withwastewater treatment);59 activated sludge pretreatment, to reduce organicnitrogen, before fungi decoloration;144 fungi pretreatment before anaero-bic treatment;58 combined fungi (biofilm) and activated sludge culture98 fordecoloration; activated algae reactor (with mixed population of algae andbacteria);13 activated sludge followed by over land flow;185 etc.
4.2. Hybrid Technologies Based on Biological Processes
Table 4 summarizes a broad spectrum of intriguing reports on hybrid tech-nologies having biological processes as the core.
4.2.1. BIOLOGICAL/PHYSICOCHEMICAL
As mentioned earlier, the literature is replete with examples of use of co-agulation complementary to biological decoloration. The choice between acoagulation–biological or biological–coagulation scheme depends on typeand dosage of coagulant, sludge quantity, and degree of inhibitory and non-biodegradable substances present in wastewater. Coagulation prior to biolog-ical treatment may be advantageous for alkaline wastewaters. After biologicaltreatment ferrous sulfate cannot be used because pH is close to neutral. On
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TAB
LE4
.Typ
ical
Exa
mple
sofCom
bin
atio
ns
Bet
wee
nB
iolo
gica
lTre
atm
entan
dO
ther
Tech
nolo
gies
Tech
nolo
gyD
ye/w
aste
wat
erD
etai
lsRef
eren
ce(y
ear)
Chem
ical
(NaO
Cl)/b
io(a
nae
robic
)K
raft
E1
effluen
t(c
onta
inin
glig
nin
and
oth
erco
lore
dco
mpounds
like
quin
ones
,ch
alco
nes
,st
ilben
es)
NaO
Cl(0
.1kg
Cl/
kgco
lor;
pH
=10
)ac
hie
ved
90%
colo
rre
mova
lw
ith50
%in
crea
sein
low
mole
cula
rm
ass
AO
X,w
hic
hw
asam
enab
leto
subse
quen
tan
aero
bic
trea
tmen
t,al
though
asi
multa
neo
us
smal
lam
ountofco
lor
reve
rsio
nocc
urr
edduring
anae
robic
stag
e.A
short-ter
mso
lutio
nfo
rco
mbin
eddec
olo
ratio
n&
dec
hlo
rinat
ion.
47(1
994)
Poly
ure
than
eim
mobili
zed
fluid
ized
bio
film
/coag
ula
tion
(alu
m)
Dye
ing
was
tew
ater
from
poly
este
rdew
eigh
ted
pro
cess
92%
CO
DM
n(initi
ally
824
mg/
L)re
mova
lby
bio
logi
cal(0
.16–
0.32
kgCO
DM
n/k
gVSS
.day
)fo
llow
edby
coag
ula
tion
(600
mg/
Lal
um
,pH
=6)
pro
cess
.Coag
ula
tion
(100
0m
g/L
alum
,pH
=6)
follo
wed
by
bio
logi
cal(0
.09–
0.19
kgCO
DM
n/k
gVSS
.day
)pro
cess
achie
ved
sim
ilar
rem
ova
l,butw
ith20
%m
ore
exce
sssl
udge
due
tom
ore
dis
solv
ed(in
additi
on
tosu
spen
ded
)su
bst
ance
rem
ova
lduring
coag
ula
tion.
229
(199
6)
Coag
ula
tion
(Na-
ben
tonite
)/ac
tivat
edsl
udge
Was
tew
ater
from
pla
nts
dye
ing
&finis
hin
gnat
ura
l/sy
nth
etic
fiber
s
Chem
ical
pre
trea
tmen
t(2
g/L)
prior
tobio
logi
calpro
cess
reduce
d40
%ofin
itial
bio
deg
radab
leas
wel
las
iner
tso
luble
CO
D,th
ereb
yre
duce
dpote
ntia
lof‘res
idual
iner
tCO
D(p
roduct
sfr
om
bio
deg
radab
leCO
D)’,w
hile
chem
ical
post
trea
tmen
tfo
llow
ing
bio
logi
cal,
achie
ved,des
pite
bet
ter
dec
olo
ratio
n,only
20%
resi
dual
solu
ble
CO
Dre
mova
l.
57(2
002)
Fluid
ized
bio
film
/coag
ula
tion/
elec
troch
emic
aloxi
dat
ion
Synth
etic
text
iledye
ing
was
tew
ater
Bio
film
ofsp
ecia
llyis
ola
ted
mic
robes
on
support
med
iaac
hie
ved
68.8
%CO
Dcr
(initi
al=
800–
1000
mg/
L)an
d54
.5%
colo
rre
mova
lw
hile
those
achie
ved
by
ove
rall
com
bin
edsy
stem
(FeC
l 3.6
H2O
dose
of3.
25x
10−3
mol/
L;Ele
ctro
oxi
dat
ion:2.
1m
A/c
m2
ofcu
rren
tden
sity
and
0.7
L/m
inflow
rate
)w
ere
95.4
%an
d98
.5%
,re
spec
tivel
y.
100
(200
2)
Fento
nor
pow
der
edac
tivat
edC
(PA
C)/
fixe
dbed
bio
film
/Fen
ton
Dis
per
sedye
stuff
was
tew
ater
Enhan
ced
rem
ova
lby
pre
viousl
yac
clim
atiz
edbio
mas
son
fixe
dbed
due
toin
crea
sed
bio
deg
radab
ility
(BO
D5:C
OD
from
0.06
to0.
432)
by
Fento
n(H
2O
2:Fe
SO4·7H
2O
=70
0:35
00,m
g/L)
or
PAC
pre
trea
tmen
t.CO
Dre
mova
l(initi
ally
1720
0m
g/L)
sepa
rate
lyat
pre
trea
tmen
t,bio
logi
cal&
post
trea
tmen
tw
ere
50%
,85
%&
85%
,re
spec
tivel
y.
3(1
999)
(Con
tin
ued
on
nex
tpa
ge)
341
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TAB
LE4
.Typ
ical
Exa
mple
sofCom
bin
atio
ns
Bet
wee
nB
iolo
gica
lTre
atm
entan
dO
ther
Tech
nolo
gies
(Con
tin
ued
)
Tech
nolo
gyD
ye/w
aste
wat
erD
etai
lsRef
eren
ce(y
ear)
Coag
ula
tion/
elec
troch
emic
aloxi
dat
ion/a
ctiv
ated
sludge
15dye
suse
din
apla
nt
mak
ing
prim
arily
cotton
and
poly
este
rfiber
san
dsm
allquan
tity
ofw
ool
Influen
t:CO
D=
800–
1600
mg/
L,Tra
nsp
aren
cy<
4cm
,Conduct
ivity
=20
00μ
mho/c
m,pH
=6–
9.CO
Dco
nce
ntrat
ion
(100
mg/
L)an
dtran
spar
ency
(30)
amply
satis
fies
the
gove
rnm
entsa
fedis
char
gest
andar
dby
emplo
ying
Poly
alum
inum
chlo
ride
(40
mg/
L,w
ithpoly
mer
conce
ntrat
ion
0.5
mg/
L),el
ectroch
emic
aloxi
dat
ion
(pH
≈7,
curr
entden
sity
=53
.4m
A/c
m2,1
L/m
inofflow
rate
)an
dth
esu
bse
quen
tac
tivat
edsl
udge
pro
cess
.
129
(199
6)
Bio
/ele
ctro
flocc
ula
tion/
flota
tion/fi
ltrat
ion
Was
tew
ater
from
pla
nts
dye
ing
&finis
hin
gnat
ura
l/sy
nth
etic
fiber
s
Alth
ough
elec
troflocc
ula
tion
isef
fect
ive
with
outbio
logi
cal
pre
trea
tmen
t,th
esa
me
enhan
ced
itsper
form
ance
,w
hile
subse
quen
tflota
tion
and
ben
tonite
filtr
atio
nco
mple
ted
sludge
rem
ova
l&
low
ered
Feco
nce
ntrat
ion,th
eco
mbin
edsy
stem
achie
ving
com
ple
teco
lor,
69%
CO
D&
appre
ciab
lesa
ltre
mova
l.A
l-el
ectrode
should
be
pre
ferr
edto
Fe-e
lect
rode
toav
oid
resi
dual
Fein
terf
erin
gre
use
of
was
tew
ater
for
dye
ing
lightco
lors
.
43(2
001)
O3/c
oag
ula
tion/a
ctiv
ated
sludge
Text
ilew
aste
wat
erCom
ple
tedec
olo
riza
tion
ofth
ete
xtile
effluen
t(C
OD
=18
00m
g/L,
JTU
tran
spar
ency
=2
cm)
acco
mplis
hed
with
10m
inozo
nat
ion
(rat
e13
.25
g/h).
With
out/
With
coag
ula
tion
(3m
lPA
C)
only
5%an
dup
to70
%CO
Dre
duct
ion,re
spec
tivel
y.
127
(199
3)
Coag
ula
tion/a
ctiv
ated
sludge
/ove
rlan
dflow
Cotton
text
ilew
aste
wat
erIn
putCO
D,TD
San
dTurb
idity
(200
9m
g/L,
2987
mg/
L,10
2N
TU
)re
duce
das
follo
ws:
After
Phys
icoch
emic
al[A
lum
416
mg/
L,lim
e 213
mg/
L,
poly
elec
troly
te11
mg/
L]:
(105
4m
g/L,
1540
mg/
L,52
NTU
);A
fter
Act
ivat
edsl
udge
[HRT
=20
hr,
CO
Dlo
adin
g-0.
9kg
CO
D/m
3,
MLS
S-30
73m
g/L,
sludge
recy
cle-
20%
]:(4
88m
g/L,
772
mg/
L,49
NTU
);A
fter
land
trea
tmen
t:(8
9m
g/L,
239
mg/
L,20
NTU
);
185
(199
6)
Bio
/ele
ctro
chem
ical
+H
2O
2/c
oag
ula
tion/i
on
exch
ange
Dye
ing
&finis
hin
gw
aste
wat
erEle
ctro
chem
ical
(DC
2.5A
;20
0m
g/L
H2O
2;pH
=3;
10m
in)
&co
agula
tion
(100
mg/
LPA
C,1
mg/
Lpoly
mer
)on
bio
logi
cally
pre
trea
ted
was
tew
ater
(CO
D=
111
mg/
L;Conduct
ivity
=48
50μ
mho/c
m)
achie
ved
72.8
%CO
D&
97.3
%co
lor
rem
ova
l,w
hile
subse
quen
tio
nex
chan
ge(c
atio
nic
=40
,an
ionic
=20
g/L)
reduce
dco
nduct
ivity
&CO
Dto
10μ
mho/c
m&
10m
g/L.
[Reu
sable
]
130
(199
6)
Coag
ula
tion/a
ctiv
ated
sludge
,A
S/filtr
atio
n/
dis
infe
ctio
n
Text
ilew
aste
wat
er[B
OD
5(m
g/L)
,CO
D,Conduct
ivity
(μs/
cm)]:In
fluen
t=
[940
,25
60,
3500
];A
fter
chem
ical
trea
tmen
t(F
eSO
4.7H
2O
=0.
72kg
/m3,
Poly
elec
troly
te=
0.2
g/m
3)=
[512
,12
50,29
40];
After
tertia
ry=
[15,
310,
2800
],re
usa
ble
for
irriga
tion.
155
(199
2)
342
Dow
nloa
ded
by [
Kan
sas
Stat
e U
nive
rsity
Lib
rari
es]
at 0
5:45
01
Dec
embe
r 20
13
Bio
(Ph
an
eroch
aet
ech
ryso
spori
um
fungi
)/O
3
Text
ilew
aste
wat
erD
ecre
ase
inhig
hm
ole
cula
rm
ass
frac
tion
ofte
xtile
effluen
tin
the
bio
logi
calpro
cess
(pH
=4.
5)&
low
mole
cula
rm
ass
frac
tion
during
subse
quen
tO
3trea
tmen
t(p
H=
11,15
L/h,80
min
)ac
com
pan
ied
by
40%
dec
olo
ratio
nin
each
step
,th
efinal
effluen
tsh
ow
ing
no
toxi
city
.
115
(200
1)
Bis
ulfi
te-c
atal
yzed
Na-
boro
hyd
ride
reduct
ion
/bio
Direc
tN
=Nre
d23
,D
isper
seN
=Nye
llow
5,A
cid
N=N
yello
w17
,B
asic
N=N
blu
e41
,Rea
ctiv
eN=N
ora
nge
13
Dye
:D
epen
din
gon
dye
(200
mg/
L),85
–98%
dec
olo
ratio
nw
ithin
10–3
0m
inby
chem
ical
reduct
ion.
Act
ua
lw
ast
ewa
ter
(CO
D=
770
mg/
L):[C
OD
&co
lor
rem
ova
l]:i)
Na 2
S 2O
5(2
00–2
50m
g/L)
–ca
taly
zed
NaB
H4
(50–
60m
g/L)
reduct
ion
=[7
3–86
%,8–
12%
];ii)
Subse
quen
tbio
logi
caloxi
dat
ion
=[7
4–87
%,74
–76%
].
71(2
003)
Bio
/photo
reac
tor
Rea
ctiv
e(C
ibac
ron
red
FB),
Dis
per
salYel
low
C-4
R,
Direc
t(S
olo
phen
ylO
range
T4R
L)
[CO
Dre
mova
l,ye
llow
/red
colo
rre
mova
l]:O
nly
bio
logi
cal
[HRT
3day
s,SR
T20
day
s]:[6
0%,10
–15%
/notsi
gnifi
cant];
Only
photo
reac
tor [4
gTiO
2/15
0g
zeolit
e,Li
ght
(365
nm
)in
tensi
ty30
W/m
2,20
0hrs
]:
[>90
%,co
mple
tely
dec
olo
roze
d],
bio
-photo
reac
tor [2
4h
illum
inat
ion]:
[>90
%;co
mple
tedec
olo
riza
tion]
121
(199
7)
Photo
chem
ical
/bio
(Fungi
)K
raft
E1
effluen
t(c
onta
inin
glig
nin
and
colo
red
com
pounds
like
quin
ones
,ch
alco
nes
,st
ilben
es)
Only
photo
cata
lysi
s[5
0m
gsa
nd-im
mobili
zed
ZnO
(10%
,w/w
)/1
0ml
effluen
t;Li
ght(2
54nm
)in
tensi
ty=
108W
/m2;pH
=6.
5;2h
r]:10
0%dec
olo
ratio
n,80
%CO
2fo
rmat
ion,90
%CO
Dre
duct
ion;O
nly
bio
=57
%dec
olo
ratio
n;photo
(10m
in)-
bio
(Le
nti
nu
laed
od
esfu
ngi
,96
h):
73%
dec
olo
ratio
n,;
bio
(5d
+3
d,2
cycl
es)-
photo
(20
min
):10
0%dec
olo
ratio
n
178
(199
8)
Thin
-film
photo
reac
tor
conta
inin
gphoto
synth
etic
bac
teria
Aci
dN
=Nblu
e92
TiO
2-c
oat
edre
acto
rirra
dia
ted
with
UV
and
fluore
scen
tlig
ht(3
ofea
chty
pe
at6
W)
faci
litat
eddec
olo
riza
tion
effici
ency
(80%
;15
mg
dye
/gM
LSS/
d)
ofphoto
synth
etic
bac
teria
(with
outan
yin
hib
ition
induce
dby
UV
radia
tion)
by
avoid
ing
alga
lgr
ow
than
dits
adhes
ion
on
reac
tor.
83(2
003)
Fe(I
II)/
photo
(sola
r)as
sist
edbio
logi
cal
syst
em
5-am
ino-6
-met
hyl
-2-
ben
zim
idaz
olo
ne
(AM
BI)
;dye
inte
rmed
iate
The
300
min
(shortes
tposs
ible
toyi
eld
the
bes
tco
mbin
edre
sult)
aera
ted,Fe
(III
)/lig
htpre
trea
tmen
t(F
e+3=
1m
mol/
L;40
0W
;80
mW
cm−2
)ac
hie
ved
100%
AM
BI(1
mm
ol/
L)deg
radat
ion
and
40%
DO
Cre
mova
l,w
hile
subse
quen
tim
mobili
zed
bio
logi
calco
lum
n(6
L/h)
com
ple
ted
the
min
eral
izat
ion.Pilo
t-sc
ale
inve
stig
atio
nunder
sola
rra
dia
tion
reco
mm
ended
Fe(I
II)/
H2O
2/l
ightfo
r10
times
fast
erre
actio
n.
187
(200
3)
(Con
tin
ued
on
nex
tpa
ge)
343
Dow
nloa
ded
by [
Kan
sas
Stat
e U
nive
rsity
Lib
rari
es]
at 0
5:45
01
Dec
embe
r 20
13
TAB
LE4
.Typ
ical
Exa
mple
sofCom
bin
atio
ns
Bet
wee
nB
iolo
gica
lTre
atm
entan
dO
ther
Tech
nolo
gies
(Con
tin
ued
)
Tech
nolo
gyD
ye/w
aste
wat
erD
etai
lsRef
eren
ce(y
ear)
Ele
ctro
n-b
eam
trea
tmen
t/bio
Mix
edra
ww
aste
wat
erpre
dom
inat
ely
from
dye
ing
pro
cess
&8%
from
poly
este
rfiber
pro
duct
ion
Pilo
tpla
ntin
vest
igat
ion
(flow
rate
=10
00m
3/d
)in
volv
ing
low
dose
(1kG
y)E-b
eam
pre
trea
tmen
tre
veal
eden
han
ced
bio
trea
tmen
tper
form
ance
requirin
gre
duce
d(h
alf)
resi
den
cetim
e(H
RT)
for
sam
edeg
ree
ofre
mova
l.W
ithth
ew
aste
wat
erbei
ng
origi
nal
lybio
deg
radab
le,th
ero
leofE-b
eam
was
,in
contras
tto
usu
alan
ticip
atio
nofco
nve
rsio
nofnonbio
deg
radab
leportio
n,to
conve
rtth
ebio
deg
radab
leportio
nto
further
easi
erfo
rms.
81(2
004)
AO
P(P
eroxo
n,O
3+
H2O
2;photo
-Fen
ton
with
ozo
ne,
O3+
H2O
2+
UV
+Fe
+2)
/bio
4,4′ -D
initr
ost
ilben
e-2,
2′ -dis
ulfonic
acid
(DN
S)C=C
,fluore
scen
tw
hite
nin
gag
entpre
curs
or
[Initi
al:CO
D=
2840
mg/
L;B
OD
28/C
OD
=0.
04].
Per
oxo
n(M
ola
rra
tio,
DO
C:O
3:H
2O
2=
1:1:
1/3)
or
photo
-Fen
ton
with
ozo
ne
(DO
C:O
3:H
2O
2:Fe
+2=
1:0.
3:1:
1/20
;U
V15
0W
)re
aliz
edsi
mila
r60
%CO
D,50
%D
OC
&60
%A
OX
rem
ova
l,w
hile
the
bio
deg
radat
ion
of
the
5tim
esdilu
ted
pre
oxi
diz
edsa
mple
achie
ved
ove
rall
80%
CO
Dre
mova
l.So
leozo
nat
ion,how
ever
,ac
hie
ved
bet
ter
dec
olo
ratio
nth
anth
eab
ove
two.In
situ
.OH
form
atio
nw
ithoutnee
dofU
Vre
com
men
ded
due
tost
rong
UV-a
bso
rbin
gco
mpounds
inth
isw
aste
wat
er.
85(2
003)
Bio
/AO
P(P
eroxo
n,
O3+H
2O
2)/
bio
Stilb
eneC
=C-b
ased
fluore
scen
tw
hite
nin
gag
ent
[Initi
al:CO
D=
1980
mg/
L;B
OD
28/C
OD
=0.
44].
AO
Ppre
trea
tmen
tprior
bio
logi
caltrea
tmen
tdid
nothav
ean
yim
pro
vem
entef
fect
ove
rso
lebio
deg
radat
ion;hen
cea
reve
rsed
sequen
cew
asad
opte
d.
Bio
logi
calpre
trea
tmen
tre
move
d60
%CO
D&
55%
DO
C(D
isso
lved
Org
anic
Car
bon)
while
the
final
bio
deg
radat
ion
follo
win
gth
ein
term
edia
teA
OP
(Mola
rra
tio,D
OC:O
3:H
2O
2=
1:1:
1/3)
trea
tmen
tac
hie
ved
anove
rall
84%
CO
D&
71%
DO
Cre
mova
l.
85(2
003)
Cla
riflocc
ula
tion/b
io/A
OP
(H2O
2/U
V)
Woolsc
ouring
effluen
tCla
riflocc
ula
tion
follo
wed
by
aero
bic
bio
logi
caltrea
tmen
tre
move
d>
90%
CO
D&
allB
OD
;how
ever
,re
mai
nin
gCO
D(1
000
mg/
L)&
inte
nse
colo
rw
arra
nte
dsu
bse
quen
tH
2O
2/U
V[M
ola
rra
tio,CO
D:
H2O
2=
1:1;
40W
]trea
tmen
tw
hic
h,des
pite
pre
sence
ofst
rong
UV
abso
rbin
gco
mpounds,
achie
ved
100%
dec
olo
ratio
n(3
0m
in),
75%
CO
D&
85%
TO
Cre
mova
l(6
0m
in)
irre
spec
tive
ofpH
.
170
(200
4)
344
Dow
nloa
ded
by [
Kan
sas
Stat
e U
nive
rsity
Lib
rari
es]
at 0
5:45
01
Dec
embe
r 20
13
Bio
/flocc
ula
tion/O
3+
H2O
2
Text
ilew
aste
wat
erA
ctiv
ated
sludge
trea
tmen
tfo
llow
edby
flocc
ula
tion
real
ized
85%
,99
.5%
&85
%D
OC,B
OD
&CO
Dcr
rem
ova
l(I
niti
alva
lues
,m
g/L,
277,
220,
780)
,w
hile
subse
quen
tO
3+
H2O
2trea
tmen
t(6
0m
in;
[H2O
2]:[
DO
C]=
1:1)
achie
ved
com
ple
tere
mova
lofB
OD
&ove
r50
%re
mova
lofre
sidual
DO
C,CO
Dcr
.Conve
rsel
y,si
ngl
eozo
nat
ion
resu
lted
inlo
wer
CO
Dre
mova
lan
din
crea
sed
BO
D(b
iodeg
radab
ility
).
126
(200
4)
[O3]/
bio
/[O
3]
Was
tew
ater
from
pla
nts
dye
ing
&finis
hin
gnat
ura
l/sy
nth
etic
fiber
s
Pre
ozo
nat
ion,due
tose
lect
ive
pre
fere
nce
ofO
3fo
rsi
mple
rorg
anic
com
pound,si
gnifi
cantly
dec
reas
edre
adily
bio
deg
radab
leCO
Dw
ithoutap
pre
ciab
lyaf
fect
ing
solu
ble
iner
tCO
D.Post
ozo
nat
ion
achie
ved
hig
her
colo
ran
din
ertCO
Dre
mova
lin
volv
ing
50%
less
ozo
ne
dose
com
par
edto
pre
ozo
nat
ion
atsa
me
conta
cttim
e&
ozo
ne
flux
rate
.
158
(200
2)
Bio
/san
dfilte
r(S
F)/O
3W
aste
wat
erfr
om
pla
nts
dye
ing
&finis
hin
gnat
ura
l/sy
nth
etic
fiber
s
Rem
ova
lofsu
spen
ded
solid
(&hen
ceCO
D)
by
bio
logi
cal&
SFpre
trea
tmen
ten
han
ced
subse
quen
ttw
ose
quen
ces
ofozo
nat
ion
(30
min
,40
g/m
3),
achie
ving,
inco
ntras
tto
60%
CO
Dre
mova
lby
ozo
nat
ion
alone
(with
outpre
trea
tmen
t),a
com
bin
ed65
%&
78%
CO
Dre
mova
laf
ter
firs
t&
seco
nd
ozo
nat
ion
cycl
e,re
spec
tivel
y.Com
ple
tedec
olo
ratio
nal
low
edw
aste
wat
erre
use
indye
ing
even
lightco
lors
.
43(2
001)
Bio
(anae
robic
/aer
obic
)/O
3/b
io(A
erobic
)Se
greg
ated
conce
ntrat
eddye
bat
hco
nta
inin
gC.I
reac
tive
Bla
ck5
&hig
hsa
ltco
nce
ntrat
ions.
Alth
ough
bio
logi
calpre
trea
tmen
tac
hie
ved
>70
%dec
olo
ratio
n,an
dozo
nat
ion
incr
ease
dbio
deg
radab
ility
info
llow
ing
aero
bic
reac
tor,
hig
hozo
ne
dose
of6
gO3/g
DO
Cw
asre
quired
toac
hie
veco
mbin
ed>
95%
dec
olo
ratio
n&
80%
DO
Cre
mova
lw
hile
notm
ore
than
30%
DO
Cw
asre
move
dby
bio
logi
calre
acto
r;in
tern
alre
cycl
ebet
wee
nozo
nat
ion
&ae
robic
stag
ere
com
men
ded
for
reduci
ng
ozo
ne
dose
.
124
(200
3)
Bio (a
nae
robic
–aer
obic
)/O
3
Colo
red
was
tew
ater
conta
inin
gm
elan
oid
ins
Ozo
nat
ion
(1.6
g/h–
11.5
g/h)
ofbio
logi
cally
(anae
robic
–aer
obic
)pre
trea
ted
was
tew
ater
(CO
D=
4580
,TO
C=
1000
,m
g/L)
achie
ved
71–9
3%dec
olo
ratio
n&
15–2
5%CO
Dre
mova
lin
30m
in
165
(200
3)
(Con
tin
ued
on
nex
tpa
ge)
345
Dow
nloa
ded
by [
Kan
sas
Stat
e U
nive
rsity
Lib
rari
es]
at 0
5:45
01
Dec
embe
r 20
13
TAB
LE4
.Typ
ical
Exa
mple
sofCom
bin
atio
ns
Bet
wee
nB
iolo
gica
lTre
atm
entan
dO
ther
Tech
nolo
gies
(Con
tin
ued
)
Tech
nolo
gyD
ye/w
aste
wat
erD
etai
lsRef
eren
ce(y
ear)
Bio
(anoxi
c/ae
robic
)/O
3Rea
ctiv
eN=N
bla
ck5
(vin
ylsu
lfonic
acid
),Rea
ctiv
eN=N
red
198
(vin
ylsu
lfonic
acid
&tria
zine)
,Rem
azolD
unke
lbla
uH
R(M
etal
lized
azo)N
=N,
Rem
azolG
old
gelb
RN
LN=N
,Rea
ctiv
eN=N
yello
w25
(Dic
hlo
roquin
oxa
line)
,Rea
ctiv
eN=N
Red
159
(Dic
hlo
rofluro
pyr
imid
ine)
Sequen
cing
anoxi
c/ae
robic
pro
cess
along
with
par
tialoxi
dat
ion
by
ozo
nat
ion
(concu
rren
tw
ithae
robic
phas
e)in
are
circ
ula
ted
syst
emyi
elded
com
ple
tedec
olo
ratio
nan
dsh
ow
edsy
ner
gist
icen
han
ced
bio
logi
calD
OC
rem
ova
l(9
0%)
asw
ellas
low
erco
nsu
mptio
nof
O3(5
mg/
mg
DO
C).
111
(199
8)
Bio
logi
cal+
phys
icoch
emic
al/O
3
Jean
sfinis
hin
gpla
nt
was
tew
ater
mix
edw
ithdom
estic
WW
(<30
%)
Pre
trea
tmen
tin
volv
ing
GA
C(2
00g/
8L)
&poly
elec
troly
tead
diti
on
inan
aero
bic
reac
tor
rest
ore
dnitr
ifica
tion
activ
ity&
impro
ved
sludge
settle
abili
tyofth
esu
bse
quen
tae
robic
reac
tor
with
acu
mula
tive
96%
CO
D&
88%
colo
rre
mova
l,w
hile
follo
win
gozo
nat
ion
achie
ved
70%
reusa
ble
wat
er.
205
(199
9)
Bio
/O3
Nap
hth
alen
e-1,
5-dis
ulfonic
acid
(NA
DSA
),a
dye
pre
curs
or
Com
bin
edfixe
d-b
edbio
reac
tor
(equip
ped
with
a1.
5μ
mm
embra
ne
for
solid
/liq
uid
separ
atio
n)
and
ozo
nat
ion
trea
tmen
tin
sem
icontin
uous
fash
ion
achie
ved
ca.80
%D
OC
rem
ova
l(I
niti
al=
170–
340
mg/
L)w
ith>
50%
reduct
ion
inozo
ne
consu
mptio
n(0
.8m
ol
O3/m
olD
OC)
asco
mpar
edto
singl
euse
ofozo
nat
ion
only
.
30(2
003)
Bio
/O3/g
ranula
rac
tivat
edC(G
AC)
Dom
estic
+te
xtile
indust
ry(5
0–70
%)
was
tew
ater
Feed
wat
er[o
nG
AC]:
CO
D=
128–
135
mg/
L,TO
C=
16–1
8m
g/L;
C-a
dso
rptio
nis
less
effe
ctiv
eaf
ter
the
ozo
nat
ion,re
sidual
CO
D(>
70)
&co
lor
(ove
roptic
aldet
ectio
n)
unsu
itable
for
reuse
;“B
io+F
locc
ula
tion+O
3+G
AC”
pro
pose
d.
23(1
999)
O3/b
iolo
gica
lac
tivat
edC
(BA
C)
Nat
ura
lco
loring
mat
ter
(Hum
icsu
bst
ance
s)B
iodeg
radab
leD
OC
incr
ease
dby
pre
ozo
nat
ion
was
subse
quen
tlybio
deg
raded
rath
erth
anbei
ng
sim
ply
adso
rbed
on
BA
Can
d,
ther
eby,
incr
ease
dB
AC
serv
ice
time.
221
(199
7)
Coag
ula
tion
or
cata
lytic
H2O
2/b
ioB
asic
dye
Chem
ical
pre
cipita
tion
(FeC
l 3=
400
mg/
L;pH
=9.
5),des
pite
resu
lting
in41
%CO
Dre
mova
lfr
om
raw
was
tew
ater
,co
uld
notim
pro
vebio
deg
radab
ility
.A
fter
par
tialoxi
dat
ion
(H2O
2/C
OD
=1;
Fe+3
=50
0m
g/L;
pH
=3.
5;1
day
)63
%CO
Dre
mova
l&
was
tew
ater
bio
deg
radab
ility
was
achie
ved.
15(1
999)
346
Dow
nloa
ded
by [
Kan
sas
Stat
e U
nive
rsity
Lib
rari
es]
at 0
5:45
01
Dec
embe
r 20
13
Bio
logi
calfixe
dG
AC
bed
Aci
dN
=N(T
ectil
on
Red
2B,
Tect
ilon
ora
nge
3G)
GA
Cbed
inocu
late
dw
ithsp
ecia
lch
rom
ophoric
bond-c
leav
ing
&ar
om
atic
ring-
clea
ving
bac
teria,
afte
rin
itial
accl
imat
izat
ion
per
iod,
outp
erfo
rmed
conve
ntio
nal
GA
Cbed
;th
ebac
terial
activ
ity,how
ever
,dec
reas
edaf
ter
certai
nper
iod
due
tola
ckofnutrie
ntan
d/o
rdis
solv
edoxy
gen.[D
ye=
100
mg/
L].
218
(199
6)
Bio
(anoxi
c/ae
robic
)/o
xyge
nen
rich
edB
AC
Mix
edte
xtile
dye
ing–
printin
g(R
eact
ive
blu
edye
)an
dal
kali
pee
ling
was
tew
ater
The
initi
alco
nta
ctbio
-film
syst
emim
pro
ved
bio
deg
radab
ility
while
subse
quen
tB
AC
syst
em,due
toen
han
ced
bio
deg
radat
ion
induce
dby
hig
hD
Ole
velm
ainta
ined
by
hig
hpre
ssure
(0.4
Mpa)
,ac
hie
ved
hig
htu
rbid
ity,co
lor,
CO
D,&
NH
3-N
rem
ova
lw
ithco
ncu
rren
tpro
longe
dca
rbon-b
edlif
e,th
eper
form
ance
esse
ntia
llybei
ng
bet
ter
than
norm
alB
AC
or
pure
GA
Cpro
cess
.
177
(200
4)
Bio
logi
calfluid
ized
GA
Cbed
Ble
ached
kraf
tm
illse
condar
yef
fluen
tco
nta
inin
gre
frac
tory
org
anic
slik
elig
nin
,w
hic
hm
aybe
consi
der
edto
be
repre
senta
tive
ofdye
stru
cture
.
57%
DO
Cre
mova
l(initi
al=
280–
330
mg/
L;0.
9g
DO
C/k
gA
C.d)
by
phys
ical
adso
rptio
non
GA
Can
dbio
mas
sfo
llow
edby
bio
deg
radat
ion
&des
orp
tion
achie
ving
par
tialbio
rege
ner
atio
nof
GA
Cw
asobse
rved
.Com
bin
ed‘b
iore
gener
atio
n/p
hys
ical
(US–
IR)–
par
tialre
gener
atio
n(5
0%ofG
AC
volu
me)
’ach
ieve
d30
–40%
impro
ved
rem
ova
lw
ith2%
wei
ghtlo
ss/r
egen
erat
ion,w
hic
his
smal
ler
than
loss
due
toso
lere
gener
atio
nby
phys
ical
met
hod.
217
(199
4)
Bio
+re
circ
ula
ted
pow
der
edac
tivat
edC
(PA
C)
/flocc
ula
tion
Dom
estic
effluen
tm
ixed
with
reac
tive
dye
(Cib
acorn
yello
wCR01
,Cib
acorn
yello
wF3
R,
Cib
acorn
red
C2G
,Cib
acorn
red
CR,
Cib
acorn
Red
FB,
Cib
acorn
blu
eFB
,Le
vafix
yello
wK
R,Le
vafix
red
KG
R,Rem
azolre
d,
Rem
azolbla
ck)
/sal
ts/a
uxi
liary
chem
.
[Initi
alCO
D=
775–
4035
,pH
=9–
12];
Rec
ircu
latio
nofPA
C(1
3m
g/L)
resu
lted
inef
fect
ive
rem
ova
lofdye
san
dhal
oge
nat
ed/r
efra
ctory
org
anic
sal
ong
with
optim
um
use
ofPA
Cw
hic
his
only
par
tially
load
edif
notre
cycl
ed.
156
(199
9)
Pow
der
edac
tivat
edca
rbon
or
org
anic
flocc
ula
ntad
diti
on
inbio
logi
calsy
stem
Cotton
text
ilew
aste
wat
erO
nly
bio
(SRT
=30
day
s,H
RT
=16
day
s):94
%CO
Dre
mova
l,36
%dec
olo
ratio
n.Com
bin
ed(P
AC
=20
0m
g/L
or
Org
anic
flocc
ula
nt=
120
mg/
L):D
ecolo
ratio
nim
pro
ved
up
to78
%,th
eorg
anic
flocc
ula
nt
pro
duci
ng
less
exce
sssl
udge
than
PAC.
161
(200
2)
Pow
der
edac
tivat
edca
rbon
additi
on
inbio
logi
calsy
stem
(PA
CT)
Aci
dN
=Nora
nge
7,C.I.15
510
The
beh
avio
rofCO
Dre
mova
lw
asth
esa
me
butth
edye
rem
ova
lw
asbet
ter
inth
ePA
CT
than
inth
eco
nve
ntio
nal
activ
ated
sludge
pro
cess
.49
(199
7)
(Con
tin
ued
on
nex
tpa
ge)
347
Dow
nloa
ded
by [
Kan
sas
Stat
e U
nive
rsity
Lib
rari
es]
at 0
5:45
01
Dec
embe
r 20
13
TAB
LE4
.Typ
ical
Exa
mple
sofCom
bin
atio
ns
Bet
wee
nB
iolo
gica
lTre
atm
entan
dO
ther
Tech
nolo
gies
(Con
tin
ued
)
Tech
nolo
gyD
ye/w
aste
wat
erD
etai
lsRef
eren
ce(y
ear)
Pow
der
edac
tivat
edca
rbon
additi
on
inbio
logi
calsy
stem
Aci
dN
=Nora
nge
7,C.I.
1551
0U
nder
ahig
her
bio
mas
sco
nce
ntrat
ion
(>3
g/L)
,th
eca
rbon
par
ticle
sar
etrap
ped
inth
efloc
mat
rix
and
lose
thei
rpro
per
ties
ofad
sorp
tion
hin
der
ing
mic
robia
lgr
ow
than
ddye
rem
ova
l.
141
(199
7)
Pow
der
edac
tivat
edca
rbon
additi
on
inbio
logi
calsy
stem
Dis
per
sed,direc
t,ac
id&
bas
icdye
s;an
ionic
/nonio
nic
det
erge
nts
.
Rem
ova
lef
fici
ency
rise
sfr
om
55.8
to75
.6%
(CO
D)
and
from
78to
98.5
%(T
OC).
The
nitr
ifica
tion–
den
itrifi
catio
nca
pac
ityofth
esy
stem
also
incr
ease
s,pro
bab
lydue
tohig
hco
nce
ntrat
ion
of
nitr
ifyi
ng–
den
itrifyi
ng
bac
teria
on
the
PAC
surf
ace.
197
(198
4)
Fluid
ized
bed
reac
tor
conta
inin
gco
mple
xpel
lets
ofw
hite
rot
fungu
s&
activ
ated
carb
on
Aci
dN
=Nvi
ole
t7
Com
ple
xm
ycel
ium
pel
lets
with
abla
ckco
reofac
tivat
edca
rbon
(pre
par
atio
n:5
mlin
ocu
lum
+0.
6g
A.C
+200
mlm
ediu
m),
by
reta
inin
gnec
essa
ryfu
nga
lm
etab
olit
es,outp
erfo
rmed
stan
dal
one
applic
atio
noffu
ngi
or
activ
ated
C,or
even
sim
ple
additi
on
of
activ
ated
Cin
fungi
reac
tor;
the
dec
olo
ratio
n(9
5%)
bei
ng
bet
ter
inre
pea
ted
bat
chre
acto
r(5
0g
wet
com
ple
xpel
let/
L;20
hre
tentio
n;
500
mg/
Ldye
)th
anin
contin
uous
reac
tor.
235
(200
0)
Act
ivat
edca
rbon
(AC)-
amen
ded
anae
robic
bio
reac
tor
Hyd
roly
zed
reac
tiveN
=Nre
d2,
Aci
dN
=Nora
nge
7A
C,in
additi
on
toits
adso
rptio
nca
pac
ity,as
abio
logi
cally
rege
ner
able
redox
med
iato
rdue
toquin
one
surf
ace
group
on
it,en
han
ced
azo
dye
reduct
ion,ac
hie
ving
97–9
0%dec
olo
ratio
nfo
r13
0day
s[4
2m
g/L
dye
;35
g/L
VSS
;H
RT
=5.
5hr;
10g/
LA
C].
234
(200
3)
Bio
/NF
Dilu
ted
wooldye
ing
bat
hco
nta
inin
gm
etal
com
ple
x&
acid
dye
(origi
nal
dye
conce
ntrat
ion
8g/
L)
Dilu
ted
dye
bat
h(C
OD
=2
g/L)
afte
rac
tivat
edsl
udge
trea
tmen
t(C
OD
=20
0m
g/L)
was
subje
cted
tonan
ofiltr
atio
nth
atre
sulte
din
reuse
stan
dar
dper
mea
te(f
urther
99%
colo
r&
88%
CO
Dre
mova
l)w
ithle
ssfo
ulin
gas
com
par
edto
that
for
direc
tnan
ofiltr
atio
nofdye
bat
hs.
Ozo
nat
ion
ofm
embra
ne–
rete
nta
tebef
ore
recy
clin
gto
activ
ated
sludge
pro
cess
was
reco
mm
ended
.
33(2
001)
Bio
/mem
bra
ne
(+al
um
inum
poly
chlo
ride)
Dom
estic
+Te
xtile
indust
ry(8
0%by
org
anic
load
)w
aste
wat
er
Mic
rofiltr
atio
n(3
00,0
00D
,cr
oss
-flow
)fo
llow
edby
nan
ofiltr
atio
n(1
50D
,10
bar
,sp
iral
wound)
along
with
alum
inum
poly
chlo
ride
(70
mg/
L)pro
duce
dre
cycl
able
wat
er(C
OD
<10
mg/
L,co
nduct
ivity
<40
us/
cm,neg
ligib
lere
sidual
colo
r)fr
om
the
seco
ndar
yef
fluen
t;al
tern
atel
y“c
lariflocc
ula
tion
(Dose
:4
ppm
,vo
l.)+
multi
med
iafiltr
atio
n+
low
-pre
ssure
RO
(58
D,4
bar
,10
L/m
2.h
,sp
iral
wound)”
seem
edpre
fera
ble
inte
chno-e
conom
ical
anal
ysis
.
183
(199
9)
348
Dow
nloa
ded
by [
Kan
sas
Stat
e U
nive
rsity
Lib
rari
es]
at 0
5:45
01
Dec
embe
r 20
13
‘Bio
+pow
der
edac
tivat
edC,
(BPA
C)’/M
icro
filtr
atio
n
Seco
ndar
yse
wag
eef
fluen
tco
nta
inin
gre
frac
tory
org
anic
slik
elig
nin
,w
hic
hm
aybe
consi
der
edto
be
repre
senta
tive
ofdye
stru
cture
.
PAC
dose
of0.
5g/
L.52
%TO
Cre
move
din
BPA
Cco
nta
ctor
(hig
her
than
PAC
only
),ad
diti
onal
16.8
%w
asre
ject
edby
mem
bra
ne.
189
(199
7)
Bio
/NF
or
O3
Was
tew
ater
from
printin
g,dye
ing
&finis
hin
gte
xtile
pla
nt
Bio
logi
cally
trea
ted:Conduct
ivity
(mS/
cm)
2.8–
3.33
;CO
D(m
g/L)
200–
400.
Folo
win
gbio
logi
caltrea
tmen
ti)
Nan
ofiltr
atio
n(fl
ow
rate
=20
0–40
0L/
h,TM
P=
20bar
):CO
D<
50m
g/L;
Conduct
ivity
=0.
39–0
.51
mS/
cm.ii)
O3:CO
D=
286
(30
min
),70
(210
min
)iii
)O
3+U
V:CO
D<
50(3
0m
in),
<50
(210
min
).O
zonat
ed(w
ith/w
ithoutU
V)
was
tew
ater
can’t
be
reuse
dfo
rrinsi
ng
due
toneg
ligib
leco
nduct
ivity
rem
ova
lal
though
the
pro
cess
isfr
eefr
om
reje
ctst
ream
gener
atio
n.
27(2
003)
Bio
/NF/
O3
Text
ilew
aste
wat
erm
ixed
with
dom
estic
(20%
)w
aste
wat
er
Ozo
nat
ion
(12
ppm
,2h
)ofm
embra
ne
conce
ntrat
es(C
OD
=59
5,TO
C=
190,
Conduct
ivity
=5
ms/
cm,B
OD
5=
0,EC
20=
34%
,pH
=7.
9)re
sulti
ng
from
nan
ofiltr
atio
n(1
0bar
,30
0L/
h)
ofbio
logi
cally
trea
ted
seco
ndar
yte
xtile
effluen
tac
hie
ved
30%
,50
%,an
d90
%re
duct
ion
inTO
C,CO
D,an
dto
xici
ty,re
spec
tivel
y,m
akin
gth
eef
fluen
tre
cycl
able
tobio
logi
caltrea
tmen
t.
134
(199
9)
Bio
/NF/
photo
cata
lytic
mem
bra
ne
reac
tor
Text
ilew
aste
wat
erVis
ible
Ligh
tm
edia
ted
Fento
n(N
afion-F
e+3m
embra
ne,
1.78
%;H
2O
2,
10m
M)
trea
tmen
t(3
h)
ofm
embra
ne
conce
ntrat
es(C
OD
=49
6,TO
C=
110,
pH
=8)
resu
lting
from
nan
ofiltr
atio
nofbio
logi
cally
trea
ted
seco
ndar
yte
xtile
effluen
tre
sulte
din
50%
,20
–50%
,an
d50
%re
duct
ion
inTO
C,ab
sorb
ance
,an
dto
xici
ty,re
spec
tivel
y.Fu
rther
deg
radat
ion
thro
ugh
bio
logi
caltrea
tmen
tposs
ible
atlo
wco
stdue
tobio
com
pat
ible
pH
ofth
eef
fluen
t.
17(1
999)
Bio
/cla
riflocc
ula
tion/G
AC
or
bio
/mem
bra
ne
(MF
→N
F)/O
3
Text
ilew
aste
wat
erm
ixed
with
dom
estic
(25–
30%
)w
aste
wat
er
Due
toco
stofm
embra
ne
and,CO
D&
salin
ityin
crea
sein
bio
logi
cal
pla
ntby
mem
bra
ne
rete
nta
te,te
chno-e
conom
ical
anal
ysis
favo
red
post
trea
tmen
tofbio
logi
cally
trea
ted
effluen
tby
‘cla
riflocc
ula
tion
follo
wed
by
GA
Cad
sorp
tion’o
ver‘m
embra
ne
filtr
atio
n(M
Ffo
llow
edby
NF)
follo
wed
by
ozo
nat
ion’,
alth
ough
the
latter
pro
duce
dbet
ter
&co
nst
antqual
ity(s
often
ed,co
lorles
s)re
cycl
able
effluen
t.
182
(199
9)
Bio
/san
dfiltr
atio
n(S
F)/m
embra
ne
(MF
follo
wed
by
NF)
Dye
ing
was
tew
ater
100%
SS,78
%tu
rbid
ity&
30%
CO
Dre
mova
lby
SF(2
bar
)&
MF
(3.5
bar
;40
0L/
h);
13%
colo
rre
mova
lby
MF,
and
rem
ainin
gCO
D&
colo
rre
mova
lby
NF
(6.5
–7bar
)co
ntrib
ute
dto
ove
rall
94%
colo
r&
82%
CO
Dre
mova
lal
ong
with
conduct
ivity
rem
ova
lm
akin
gth
etrea
ted
wat
erre
usa
ble
for
dye
ing.
139
(200
2)
349
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350 F. I. Hai et al.
the other hand, the dose of coagulants and consequently the quantity of thechemical sludge after biological treatment are smaller compared to those incoagulation followed by biological treatment.57,75,100
Besides coagulation, a variety of other treatment processes may be com-bined with biological treatment. Very often a certain physicochemical processis placed before129 and/or after130 an advanced oxidation process. The bio-logical process is then applied either as the very first,100 penultimate,3 or asthe last129 treatment unit. In view of the abundance of bioresistant and toxiccontaminants in dye wastewater, physicochemical and advanced oxidativepretreatment prior to biological treatment appears to be a rational option. Thechoice between physicochemical and oxidative pretreatment, however, de-pends on the specific wastewater; usually an astute stream separation wouldfacilitate application of appropriate treatment system for different streams.3
On the contrary, especially isolated/acclimatized microbes are usually re-quired for effective biological pretreatment.100,115 In order to obtain reusablewater, an elaborate treatment train composed of conventional physicochemi-cal and advanced oxidation processes may be placed after biological pretreat-ment. While numerous such combinations have been reported in literature,the common underlying principle is to choose a combination so as to furnisha complete system eliminating limitations of the individual techniques. Forinstance, the fact that high concentrations of suspended or colloidal solids inthe wastewater may impede the advanced oxidation processes necessitatessufficient prior removal of these materials by physicochemical treatment.43,100
Conversely, enhancement of COD removal (e.g., after ozonation)127 or im-provement of settleability of sludge (e.g., after electrofloatation)43,130 mayrequire physicochemical treatment subsequent to AOPs.
4.2.2. INTEGRATED PARTIAL OXIDATION/BIODEGRADATION
In contrast to the conventional pre- or posttreatment concepts, where pro-cess designs of different components are independent of each other, a ratherinnovative approach is the so-called “integrated processes” where the effec-tiveness of combining biological and other treatments is specifically designedto be synergetic rather than additive.134 A typical example of such processesis combination of advanced oxidation with an activated sludge treatmentwhere the chemical oxidation is specifically aimed to partially degrade therecalcitrant contaminants to more easily biodegradable intermediates, therebyenhancing subsequent biological unit and simultaneously avoiding the highcosts of total mineralization by AOP. During recent years myriad studies deal-ing with partial preoxidation of dye wastewater, involving virtually all sortsof AOPs, have been reported. Some of these studies include partial oxida-tion by ozonation,39 H2O2,46 photocatalysis,178 photo (solar)-Fenton,207 wetair oxidation,169 combined photocatalysis and ozonation/H2O2,146,200 pho-toelectrochemical process,6 sub- and supercritical water oxidation,103 andelectron-beam treatment.81 The bulk of such studies report on improvement
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Hybrid Treatment Systems for Dye Wastewater 351
of biodegradability (as revealed by biological oxygen demand [BOD]/CODratio or partial oxidation parameter92) and reduction of toxicity (using bioas-say, e.g., bioluminescence test) following some AOP treatment without in-volving actual experiment in biological reactor. However, complete resultsfrom actual investigation in biological system following partial oxidation,as listed in Table 4, are also available. Careful consideration of character-istics of each AOP would facilitate selection of a proper preoxidation pro-cess for rendering wastewater more amenable to biological treatment. Forinstance, Fenton-like treatment using Nafion-Fe+3 membrane, rather than di-rect addition of iron salt,17 or immobilized TiO2 photocatalysis rather thanthe photo-Fenton process,164 would facilitate further biological treatment un-der biocompatible pH making neutralization redundant. Mantzavinos et al.138
have proposed a step-by-step approach to evaluate chemical pretreatmentfor integrated systems.
The combined oxidation and subsequent biodegradation make it nec-essary to set the optimal point of oxidative treatment. Further oxidation maynot lead to any significant changes in the molecular weight distribution, butresult in an increasing mineralization of low-molecular-weight biodegradablesubstances.92 Hence it is rational to adopt the shortest possible preoxidationperiod and remove the biodegradable portion using cost-effective biologicalprocess. Nonetheless, the extent of combined COD removal achievable withthis strategy may be limited in some cases, making utilization of a longer ox-idation period necessary and the following biological process redundant.170
An internal recycle between the oxidation and biological stage has beenrecommended for reducing chemical dose in such circumstances.124 Do-gruel et al.56 pointed to the selective preference of ozone for simpler readilybiodegradable soluble COD fractions, which leads to unnecessary consump-tion of the chemical. They suggested preozonation of segregated recalcitrantstreams from the dye house prior to biological treatment of the mixed wholeeffluent. If a considerable amount of biodegradable compounds originallyexists in the wastewater, the preoxidation step obviously will not lead toa significant improvement of biodegradability; rather, it will cause unnec-essary consumption of chemicals. In such a case a biological pretreatment(removing biodegradable compounds) followed by an AOP (converting non-biodegradable portion to biodegradable compounds with less chemical con-sumption) and a biological polishing step may prove to be more useful.85,213
4.2.3. BIODEGRADATION/ADSORPTION
Owing to limited effectiveness of conventional biological treatment for re-calcitrant textile wastewater composed of recalcitrant textile chemicals anddyes, various adsorbents and chemicals,161 predominantly activated carbon,have been directly added into the activated sludge systems in certain stud-ies. The fact that the additional removal of soluble organic matter (COD andtotal organic carbon, TOC ) in such a system over that in a conventional
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352 F. I. Hai et al.
system cannot be explained by probable contribution of adsorbent as pre-dicted by adsorption isotherms141 has persuaded researchers to hypothe-size a synergistic relationship between activated carbon and microorganism(“enhanced microbial degradation and bioregeneration of adsorbent”).167 En-hanced biodegradation has been attributed to the ability of adsorbent to actas a modulator, by immediately adsorbing high concentrations of the toxiccompounds, and thus regulating the concentration of the free toxic material,together with providing an enriched environment for microbial metabolismon the liquid–solid surface, on which microbial cells, enzymes, organic ma-terials, and oxygen are adsorbed.1 Conversely, bioregeneration of activatedcarbon has been explained by extracellular biodegradation of adsorbed or-ganics by microbial enzymes excreted into carbon micropores.197,225 Themain step in dye removal for activated carbon-amended biological processis microbial degradation, which is higher than adsorption both on activatedcarbon and on biomass.49 Accordingly, although the dye removal in that pro-cess has frequently been reported to be better than in the conventional ac-tivated sludge process,161,197 the mode of COD removal may be the same.49
Under a higher biomass concentration (>3 g/L), the carbon particles are,however, trapped in the floc matrix and lose their properties of adsorption,thereby hindering microbial growth and dye removal.141 Although simultane-ous adsorption and biodegradation treatment occasionally has been demon-strated as a mere combination of adsorption and biodegradation without anymutual enhancement159 and has raised controversies in the bioregenerationhypothesis,225 application of this process to the treatment of textile wastew-aters is an important economic improvement. It allows the removal of CODand color from textile wastewater in a single step with no additional physic-ochemical treatment.141 To minimize reactor volume, a hydraulic retentiontime as low as possible is practically expected. This in turn, however, ren-ders powdered activated carbon (PAC) partially loaded. Its optimum use maybe realized by recirculation of PAC.156 In addition to its adsorption capac-ity, activated carbon has also been reported to enhance anaerobic azo dyereduction234 by acting as a biologically regenerable redox mediator due toquinone surface groups on it. Zhang et al.235 documented an innovative ap-proach involving a fluidized bed reactor containing complex pellets of whiterot fungus and activated carbon. The reactor, by retaining necessary fungalmetabolites, surpassed stand-alone application of fungi or activated C. Theprocess was claimed to be superior to simple addition of activated C in fungireactor.
Fixed granular activated carbon (GAC) beds inoculated with specialchromophoric bond-cleaving and aromatic ring- cleaving bacteria, after aninitial acclimatization period, have been reported to outperform the con-ventional GAC bed.218 However, the bacterial activity in the GAC bed maydecrease after a certain period due to lack of nutrient and/or dissolved oxy-gen (DO). Maintenance of a high DO level by a pressurized system may
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Hybrid Treatment Systems for Dye Wastewater 353
ensure achievement of stable removal (color and COD) with concurrentprolonged carbon-bed life.177 A novel approach entailing partial bioregener-ation (physical adsorption on fluidized biological GAC followed by biodegra-dation and desorption), coupled with complementary periodic physical re-generation of 50% of total GAC, has been reported by Vuoriranta et al.217
The system was observed to achieve an improved COD and color removalapart from reduction in regeneration cost and weight loss of GAC. Moreover,the system has the added advantage of allowing biological activity in GACmedium for subsequent use. Some means of improvement of biodegrad-ability, be it biological177 or advanced oxidation process221, will certainlyfortify biological activity in the subsequent biological GAC. However, in caseof oxidative degradation, subsequent substrate adsorption on carbon mayplummet.23 Carbon-biocatalyst amalgamation in adsorption cartridges for de-coloration has been commercialized (BIOCOL) in the United Kingdom.48
4.2.4. BIODEGRADATION/MEMBRANE FILTRATION
4.2.4.1. Chronological application. For reusable water production,researchers have recurrently referred to nanofiltration (or low-pressurereverse osmosis) of biologically treated colored wastewater, since thisoption involves less fouling as compared to that for direct nanofiltrationof dye baths.33 Some references have put forward inclusion of sandfiltration/multimedia filtration and/or microfiltration in between biologicaltreatment and nanofiltration.139,182 Site-specific techno-economical analysisis usually recommended to ascertain the best combination.183 Notwithstand-ing the disposal problem of the reject stream emanating from membraneseparation, it may be preferred to ozonation as a posttreatment to derivereusable water from secondary wastewater, in view of the fact that the latterwould realize negligible conductivity removal.27 Conversely, provision ofadvanced oxidation of biologically treated wastewater before sending itfor nanofiltration has been reported to yield further increased membranelife.28,96 Addition of facility for partial oxidative degradation (e.g., ozonation)of membrane concentrate to the aforementioned treatment train of nanofil-tration of secondary wastewater may furnish a quasi-“closed loop” system, inthat the partially oxidized products (detoxified) may be recycled to biologicaltreatment.120,134 Such practice may, however, give rise to concern aboutsalinity increase in biological plant. Wu et al.224 reported a cost-competitivedye wastewater reclamation system involving deep aeration activated sludgeprior to bioactivated carbon and nanofiltration, which, in addition to yield-ing prolonged membrane life and recovery/reuse potential, allowed directdischarge of concentrated membrane retentate. Illustrations of chronologicalapplication of membrane and biological treatment in the case of segregatedtextile wastewater streams are also available. Rinsing water may be reused af-ter reclamation by membrane, while the concentrated waste may be degradedin anaerobic digester.219 This example may be further extended to filtration of
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354 F. I. Hai et al.
the segregated dye bath effluent utilizing a membrane of appropriate molec-ular cutoff size that allows passage of salt but retains dye. Consequently,dye bath water containing salt may be reused for dye bath reconstruction,while the membrane concentrate may be degraded in an anaerobic digester.
4.2.4.2. Membrane bioreactors. The membrane bioreactor (MBR),a remarkable improvement over the conventional activated sludgetreatment,214 has been set forth as a promising option in colored wastew-ater treatment. MBR for decoloration has often been envisioned in con-junction with simultaneous adsorption.189 A treatment scheme comprisingan activated carbon-amended anaerobic reactor preceding aerobic MBR re-alizes stable decoloration along with high TOC removal, with concurrentimprovement in activated sludge dewaterability and reduction in filtrationresistance.157 For reuse purpose, MBRs have occasionally been envisagedas the main treatment process prior to a polishing nanofiltration step,188
or even as the core of a rather elaborate treatment train including anaer-obic/aerobic pretreatment prior to MBR and ozonation following it.112 Aninnovative approach notable in contemporary literatures involves the mem-brane (submerged78/sidestream62,102)-separated fungi reactor, which couplesthe excellent degradation capability (due to nonspecific extracellular oxida-tive enzymes) of white-rot fungi with the inherent advantages of membranebioreactor. The MBR system has been envisaged to be capable of coping withthe impedances in implementation of white-rot fungi in large-scale industrialwaste treatment, such as rather slow fungal degradation,147 loss of the ex-tracellular enzymes and mediators with discharged water,235 and excessivegrowth of fungi.236 Development of such a system offering stable 99% decol-oration and 97% TOC removal from synthetic textile wastewater along withavoidance of membrane fouling has been recently documented.78
5. COST ANALYSIS
The overall costs are represented by the sum of the capital costs, the operatingcosts, and maintenance costs. Most costs are very site specific, and for a full-scale system these costs strongly depend on the flow rate of the effluent, theconfiguration of the reactor, the nature (concentration) of the effluent, andthe pursued extent of treatment. The location is also important, not only forits obvious influence on land price but also due to its climatic influence, forexample, duration and intensity of sunlight influencing efficiency of solar-Fenton process.187 Table 5 lists some cost values quoted in different studies.
Studies generally show that AOPs and membrane processes are morecostly than biological processes. However, because of the numerous site-specific factors and assumptions inevitably made in such estimates, a directcomparison is difficult. Especially, indiscriminate comparison of costs (inper cubic meter or per kilogram contaminant) of segregated versus mixedstreams would be simply misleading, as the latter remove significantly less
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TAB
LE5
.Cost
Info
rmat
ion
Per
tain
ing
toD
iffe
rentCom
bin
atio
ns
Purp
ose
&te
chnolo
gyCost
Dye
/was
tew
ater
Rem
arks
Ref
eren
ce(y
ear)
Direc
tnan
ofiltr
atio
nfo
rre
use
US$
0.53
–1.1
9a
m–3
Segr
egat
eddye
ing
and
rinsi
ng
was
tew
ater
Runnin
gco
st(1
5bar
,flow
rate
=4.
5m
/s,flux
=0.
2–1.
1m
3/h
)only
;sa
ving
ofw
ater
supply
cost
due
tore
cycl
ing
not
consi
der
ed.
215
(200
1)
Direc
tnan
ofiltr
atio
nfo
rre
use
US$
0.81
m−3
Was
tew
ater
from
dye
bat
hco
nta
inin
gac
id,dis
per
sean
dm
etal
com
ple
xdye
Cost
incl
udes
both
capita
l&
oper
atin
gco
st(fl
ow
rate
=10
00m
3/d
).Sa
ving
ofw
ater
supply
cost
(2–3
US$
m−3
)due
tore
cycl
ing
notco
nsi
der
ed.
108
(200
1)
Direc
tnan
ofiltr
atio
nfo
rre
use
ofw
ater
and
dye
bat
hsa
lt
US$
1.36
m−3
Rea
ctiv
edye
bat
hw
aste
wat
erco
nta
inin
ghig
ham
ountofN
aCl
Flow
rate
=20
0m
3/d
;quote
dco
sthas
bee
nca
lcula
ted
usi
ng
the
oper
atin
gan
din
vest
men
tco
stm
entio
ned
inth
ere
fere
nce
(ass
um
ing
10-y
rin
vest
men
t).A
pay
bac
kofin
vest
men
tco
stm
aybe
expec
ted
inle
ssth
an2
yrs
with
the
savi
ng
ofw
ater
supply
cost
,w
aste
wat
erdis
posa
lco
st,N
aClan
dhea
ten
ergy
.
110
(200
4)
Reu
seofw
ater
and
chem
ical
resi
dues
by
(i)
mem
bra
ne
filtr
atio
n,
(ii)
chem
ical
pre
cipita
tion,(iii)
activ
ated
C,(iv)
counte
rcurr
ent
evap
ora
tion
US$
m−3
(i)1
,(ii)1–
2,(iii)
10–1
5,(iv)
10–1
5
Rea
ctiv
edye
ing
ofco
tton
Cost
incl
udes
oper
atin
gan
din
vest
men
tco
st.
219
(199
6)
Ele
ctro
coag
ula
tion
asso
letrea
tmen
tU
S$0.
1–0.
3(k
gCO
Dre
move
d)−1
Mix
ture
ofex
hau
stdye
ing
solu
tions
Oper
atin
gco
st(incl
udin
gen
ergy
and
mat
eria
lco
st)
for
iron
and
alum
inum
elec
trode,
resp
ectiv
ely.
Labor,
mai
nte
nan
ce,an
dso
lid/l
iquid
separ
atio
nco
stnotco
nsi
der
ed.[W
aste
wat
erCO
D=
3422
mg/
L;ar
ound
70%
rem
ova
l.]
21(2
004)
Com
bin
edtrea
tmen
tw
ithH
2O
2/O
3/U
VU
S$6.
54m
−3W
aste
wat
erco
nta
inin
gdis
per
sedye
stuff
&pig
men
ts
Cost
ofco
nsu
mab
les
only
.Le
ssye
tsa
tisfa
ctory
(>90
%)
CO
Dre
mova
lby
Fento
n’s
reag
entat
alo
wer
(0.2
3U
S$)
unit
cost
.12
(200
4)
Com
bin
edtrea
tmen
tw
ithO
3/e
lect
ron
bea
mto
mee
tdis
char
gest
andar
d
US$
3.17
m−3
Mola
sses
pro
cess
ing
was
tew
ater
(inte
nse
lyco
lore
dan
dre
calc
itran
t)
Cost
incl
udes
both
capita
l&
oper
atin
gco
st(fl
ow
rate
=50
m3/h
).69
(199
8)
(Con
tin
ued
on
nex
tpa
ge)
355
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TAB
LE5
.Cost
Info
rmat
ion
Per
tain
ing
toD
iffe
rentCom
bin
atio
ns
(Con
tin
ued
)
Purp
ose
&te
chnolo
gyCost
Dye
/was
tew
ater
Rem
arks
Ref
eren
ce(y
ear)
Com
bin
edtrea
tmen
tw
ithm
ulti
stag
eco
agula
tion/O
3
1.57
CU
S$to
n−1
h−1
Dye
man
ufa
cturing
was
tew
ater
Appro
xim
ate
cost
consi
der
ing
elec
tric
ityco
stofozo
ne
gener
atio
nonly
(chem
ical
cost
mad
esm
allco
ntrib
utio
n).
86(1
998)
Com
bin
edtrea
tmen
tw
ithad
sorp
tion
+U
V–H
2O
2
US$
1m
−3Rea
ctiv
eEve
rzolB
lack
-GSP
Oper
atin
gco
st(c
onsu
mab
les
and
mai
nte
nan
ce)
for
dec
olo
ratio
n&
50%
TO
Cre
mova
lfr
om
36ppm
dye
solu
tion.
91(2
002)
Com
bin
edtrea
tmen
tw
ithcl
arifl
occ
ula
-tio
n/o
zonat
ion/m
embra
ne
(UF)
for
reusa
ble
wat
er
US$
0.52
bm
−3W
aste
wat
erfr
om
carb
oniz
ing,
dye
ing
and
fulli
ng
pro
cess
Flow
rate
=15
00m
3/d
;Cost
incl
udes
oper
atin
gan
din
vest
men
tco
st.A
pay
bac
kofin
vest
men
tco
stm
aybe
expec
ted
in3
yrw
ithth
esa
ving
ofw
ater
supply
cost
.
139
(200
2)
Photo
(sola
r)-F
ento
npre
trea
tmen
t(f
or
subse
quen
tbio
logi
cal
trea
tmen
t)
US$
22m
−3D
yein
term
edia
te(5
-am
ino-6
-met
hyl
-2-
ben
zim
idaz
olo
ne
AM
BI)
-conta
inin
gw
aste
wat
er;4
gC/L
Cost
(for
1.2
Lh
−1m
−2)
incl
udes
annual
ized
capita
l,co
nsu
mab
les
&m
ainte
nan
cebutex
cludes
hig
hla
nd
cost
(US$
200–
400
m−2
)in
Switz
erla
nd.Eco
nom
ical
than
wet
air
oxi
dat
ion
or
inci
ner
atio
n(U
S$20
0m
−3).
Further
cost
reduct
ion
poss
ible
for
dilu
ted
was
tew
ater
ata
loca
tion
pro
vidin
ghig
her
sunny
hours
.
187
(200
3)
Couple
dphoto
-Fen
ton
and
bio
logi
cal
trea
tmen
t
US$
71m
−3p-n
itroto
luen
e-ortho-
sulfonic
acid
(conta
ined
indye
man
ufa
cturing
was
tew
ater
),1
g/L
or
330
mg
C/L
Cost
of70
min
(0.6
8L/
h)
photo
-Fen
ton
pre
trea
tmen
tusi
ng
400
Wla
mp
(0.1
2U
S$/K
WH
)prior
tobio
logi
caltrea
tmen
t,co
mbin
edD
OC
rem
ova
lbei
ng
91%
.Com
mer
cial
lam
ps,
bei
ng
far
more
effici
ent,
would
incu
rle
ssco
st.
175
(199
9)
Com
bin
edtrea
tmen
tw
ithO
3/b
io(a
erobic
,ro
tatin
gdis
cre
acto
r)
US$
94.7
bm
−3Se
gre
ga
ted
conce
ntrat
eddye
bat
hco
nta
inin
gC.I
reac
tive
Bla
ck5
&hig
hsa
ltco
nce
ntrat
ions.
Cost
incl
udes
both
capita
l&
oper
atin
gco
st(fl
ow
rate
=50
L/h).
Hig
her
valu
eas
com
par
edto
those
from
oth
erst
udie
s.e.
g.,
mem
bra
ne
separ
atio
n(1
1.68
US$
m−3
),ad
sorp
tion
follo
wed
by
aero
bic
bio
logi
caltrea
tmen
t(2
.6U
S$m
−3),
pre
cipita
tion/fl
occ
ula
tion
follo
wed
by
activ
ated
carb
on
adso
rptio
n(5
.19
US$
m−3
)in
dic
ates
the
ambig
uousn
ess
aris
ing
from
stra
ightforw
ard
com
par
ison
ofco
sts
ofse
greg
ated
vs.m
ixed
stre
ams.
124
(200
3)
356
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nloa
ded
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5:45
01
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embe
r 20
13
UV
/H2O
2trea
tmen
tof
seco
ndar
yte
xtile
effluen
tto
mee
tdis
char
gest
andar
d
US$
0.85
m−3
Text
ilew
aste
wat
erO
per
atin
gco
stin
cludin
gla
mp
repla
cem
ent,
chem
ical
and
elec
tric
alco
st.(D
isch
arge
stan
dar
d:CO
D<
100
mg/
L;co
lor<
400
AD
MIunit)
123
(200
0)
Post
trea
tmen
tof
seco
ndar
yte
xtile
effluen
tby
(i)
ozo
nat
ion,(ii)
mem
bra
ne
filtr
atio
n
US$
m−3
(i)
0.19
,(ii)
0.69
Text
ilew
aste
wat
erco
nta
inin
gdirec
tan
dre
activ
edye
s
Cost
incl
udes
both
capita
l&
oper
atin
gco
st(e
xcep
tth
ere
ject
dis
posa
lco
stin
case
ofm
embra
ne
filtr
atio
n).
Flow
rate
,(a
)20
00m
3/d
;(b
)10
00m
3/d
.
108
(200
1)
Com
bin
edtrea
tmen
tw
ithco
agula
tion/
elec
troch
emic
aloxi
dat
ion/a
ctiv
ated
sludge
US$
0.34
ton
−1Te
xtile
was
tew
ater
conta
inin
g15
dye
suse
din
apla
ntm
akin
gprim
arily
cotton
and
poly
este
rfiber
san
dsm
all
quan
tity
ofw
ool
Mai
nly
cost
ofco
nsu
mab
les
incl
uded
.Eco
nom
ical
than
the
conve
ntio
nal
trea
tmen
tpro
cess
(US$
0.45
ton
−1)
use
dat
that
time
inTai
wan
.
129
(199
6)
Com
bin
edtrea
tmen
tw
ithco
agula
tion/F
ento
n’s
reag
ent/
activ
ated
sludge
US$
0.4
m−3
Text
ilew
aste
wat
erRunnin
gco
st,ex
cludin
gth
atfo
rsl
udge
dis
posa
l.Eco
nom
ical
than
the
conve
ntio
nal
trea
tmen
tpro
cess
use
dat
that
time.
128
(199
5)
Com
bin
edtrea
tmen
tw
ithCoag
ula
tion/A
ctiv
ated
sludge
/Filt
ratio
n/
Dis
infe
ctio
n
US$
0.19
–0.
22m
−3Te
xtile
was
tew
ater
Oper
atin
gco
st(c
onsu
mab
les
and
mai
nte
nan
ce)
155
(199
2)
Com
bin
edtrea
tmen
tw
ithbio
/san
dfilte
r(S
F)/O
3
for
reusa
ble
wat
er
US$
0.13
bm
−3W
aste
wat
erfr
om
pla
nts
dye
ing
&finis
hin
gnat
ura
l/sy
nth
etic
fiber
s
Cost
men
tioned
isfo
roper
atio
n&
mai
nte
nan
ce.In
cludin
gin
vest
men
tco
st,it
may
amountup
to0.
52U
S$m
−3
dep
endin
gon
amountofw
ater
trea
ted,al
though
inve
stm
ent
may
be
repai
din
ash
ort
time
due
tosa
ving
ofco
stofw
ater
supply
(0.5
2–1.
3U
S$m
−3).
43(2
001)
Com
bin
edtrea
tmen
tw
ithbio
/cla
riflocc
ula
tion/
GA
Cfo
rre
usa
ble
wat
er
US$
0.45
4bm
−3Te
xtile
was
tew
ater
mix
edw
ithdom
estic
(25–
30%
)w
aste
wat
er
Flow
rate
=25
,000
m3/d
.Cost
incl
udes
both
capita
l&
oper
atin
gco
st.
182
(199
9)
Com
bin
edtrea
tmen
tw
ithbio
/mem
bra
ne
(MF→
NF)
/O3
for
reusa
ble
wat
er
US$
1.69
-1.9
5b
m−3
Text
ilew
aste
wat
erm
ixed
with
dom
estic
(25–
30%
)w
aste
wat
er
Flow
rate
=25
,000
m3/d
.Cost
incl
udes
both
capita
l&
oper
atin
gco
st.The
syst
emm
aypote
ntia
llybec
om
eco
st-e
ffec
tive
with
dec
line
inm
embra
ne
cost
,th
em
ain
cost
-contrib
utin
gfa
ctor.
182
(199
9)
(Con
tin
ued
on
nex
tpa
ge)
357
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embe
r 20
13
TAB
LE5
.Cost
Info
rmat
ion
Per
tain
ing
toD
iffe
rentCom
bin
atio
ns
(Con
tin
ued
)
Purp
ose
&te
chnolo
gyCost
Dye
/was
tew
ater
Rem
arks
Ref
eren
ce(y
ear)
Com
bin
edtrea
tmen
tw
ithbio
/san
dfiltr
atio
n(S
F)/m
embra
ne
(MF
follo
wed
by
NF)
for
reusa
ble
wat
er
US$
0.44
bm
−3D
yein
gw
aste
wat
erFl
ow
rate
=15
00m
3/d
;Cost
incl
udes
oper
atin
gan
din
vest
men
tco
st.A
pay
bac
kofin
vest
men
tco
stm
aybe
expec
ted
in3
yrs
with
the
savi
ng
ofw
ater
supply
cost
.
139
(200
2)
Com
bin
edtrea
tmen
tw
ithbio
/san
dfiltr
atio
n(S
F)/m
embra
ne
(UF
follo
wed
by
RO
)fo
rre
usa
ble
wat
er
US$
1.26
bm
−3W
aste
wat
erfr
om
pla
nts
dye
ing
&finis
hin
gnat
ura
l/sy
nth
etic
fiber
s
Flow
rate
=10
00m
3/d
;Cost
incl
udes
both
oper
atin
gan
din
vest
men
tco
sts.
44(2
001)
Com
bin
edtrea
tmen
tw
ithdee
pae
ratio
nac
tivat
edsl
udge
/BA
C/m
embra
ne
(NF)
for
50%
recy
clin
g
US$
0.29
4C
m−3
Was
tew
ater
from
pla
nts
dye
ing
&finis
hin
gsy
nth
etic
fiber
s
Flow
rate
=50
m3/d
;Cost
men
tioned
isfo
roper
atio
n&
mai
nte
nan
ce.
224
(200
5)
Com
bin
edtrea
tmen
tw
ithbio
/san
dfiltr
atio
n(S
F)/o
zonat
ion
for
50%
recy
clin
g
US$
0.57
bm
−3W
aste
wat
erfr
om
pla
nts
fulli
ng
&dye
ing
nat
ura
l/sy
nth
etic
fiber
s
Flow
rate
=20
00m
3/d
;O
per
atin
gco
stonly
.Req
uired
fres
hw
ater
supply
(50%
ofto
tal)
incu
rsa
further
cost
of0.
92U
S$m
−3.
42(2
001)
Reu
seaf
ter
mem
bra
ne
filtr
atio
n(i),
follo
wed
by
UV
/H2O
2(ii),
concu
rren
tw
ithre
use
afte
rm
embra
ne
conce
ntrat
etrea
tmen
tby
wet
air
oxi
dat
ion
(iii)
and
bio
logi
cal(iv)
US$
m−3
(i)
0.53
(ii)2.
6(iii)
4.4
(iv)
0.13
Text
ilew
aste
wat
erFl
ow
rate
=40
0m
3/d
.In
dic
ated
cost
sar
eoper
atin
gan
dm
ainte
nan
ceco
sts
for
each
stag
eofth
ein
tegr
ated
syst
em.
Annual
ized
tota
lin
stal
latio
nco
stis
US$
243,
000
while
savi
ng
gener
ated
from
wat
erre
use
isU
S$98
,000
.
120
(200
1)
Mem
bra
ne
bio
reac
tor
US$
0.27
3m
−3M
unic
ipal
was
tew
ater
dFl
ow
rate
=2.
4m
3/h
;co
stm
entio
ned
incl
udes
allso
rts
of
capita
l&
oper
atin
gco
sts.
With
expec
ted
dec
line
inm
embra
ne
cost
toU
S$50
m−2
in20
04,th
eunit
cost
would
reduce
toU
S$0.
181
m−3
.
228
(200
4)
a,b
,cO
rigi
nal
reported
valu
esin
Deu
tsch
eM
arks
,Euro
and
Tai
wan
ese
dolla
rhav
ebee
nco
nve
rted
toU
S$by
multi
ply
ing
with
afa
ctorof0.
6633
48,1
.297
30,0
.032
2134
,re
spec
tivel
y.dD
ata
give
nfo
rco
mpar
ison
ofM
BR
tech
nolo
gyw
ithoth
ers
only
.
358
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Hybrid Treatment Systems for Dye Wastewater 359
contaminant due to dilution. The fact that treatment schemes based on segre-gated waste streams coupled with process water recycling have the potentialto save quite a bit of money even with high costs per cubic meter shouldbe considered while evaluating process viability.124 Nevertheless, the impor-tance of reporting such values cannot be overlooked as they always givesome rough idea on different scenarios and may as well form the base forfurther improved cost estimation. Plausible analyses of the cost data followin the next paragraph.
Treatment trains composed of conventional physicochemical and bio-logical systems involve sustainable cost155; however, their removal perfor-mance may not satisfy contemporary stricter regulations. Membrane filtrationof biologically pretreated dye wastewater109 has been occasionally reportedto require less cost than that for direct membrane filtration108 of dye bath,presumably as the former involves less membrane fouling. However, boththe processes furnish potential of water reuse, thereby achieving furthercost savings. Other membrane-based combinations, especially, membranebioreactors,78,228 are potential contenders among present-day dye wastewatertreatment processes. At the present stage of development of AOPs, sole ap-plication of AOP or even combinations among AOPs themselves are unlikelyto yield satisfactory effluent with reasonable cost.12 AOP pretreatment priorto biological treatment is certainly more cost-effective than complete miner-alization by AOP. Conversely, according to the examples in Table 5, AOP asa posttreatment incurs less cost as compared to that as pretreatment.109,187
Notwithstanding this fact, it should be emphasized that application of AOPpretreatment on segregated recalcitrant stream may avoid unnecessary con-sumption of chemicals by biodegradable compounds, thereby impartingcost-effectiveness to the integrated system.124 Combination of AOP withadsorption,91 membrane separation,139 or other physicochemical86 systemsmay be cost-competitive. It is intriguing to notice that integrated systemscombining a wide variety of technologies, for instance, membrane, AOP,WAO, and biological processes, when accomplishing water and/or auxiliarychemicals reuse, appear to be feasible, in that capital cost can be recoveredwithin a few years.43,120,139
6. PROPOSED HYBRID PROCESS
Based on the array of potential hybrid technologies and the available costinformation, a conceptual on-site textile dye wastewater treatment system, aspresented in Figure 3, may be proposed. Two distinct cases have been con-sidered here: (1) an integrated textile processing plant involving essentiallyall steps of textile processing, starting from conversion of fiber to cloth andextending up to dyeing and finishing, and (2) a segregated plant concerningonly dyeing and finishing. Additionally, an ideal state of practice of recovery
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360 F. I. Hai et al.
FIGURE 2. Different stages of textile wet processing and associated scopes of materialrecovery.127,220
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Hybrid Treatment Systems for Dye Wastewater 361
FIGURE 3. Layout of a conceptual on-site textile dye wastewater treatment scheme (Contin-uation from Figure 2).
and reuse of textile chemicals (sizing agent, detergent, lanolin from raw woolscouring, caustic for cotton mercerizing, dye bath electrolyte), energy (heat),and water by using appropriate membranes has been assumed (Figure 2).This assumption was prompted by the fact that such practice realizes costsavings through reduction in production of waste and consumption of freshchemicals/water, and consequently the usual payback period of the highcapital investment associated with it is 2–3 years or less.151,180 Furthermore,available technoeconomical analyses indicate that inclusion of a comprehen-sive energy and water reuse plan within the treatment scheme would be moreviable as compared to full end-of-pipe treatment with limited or no recov-ery/reuse strategy.51 Nevertheless, initial investment costs and site-specificconditions will obviously play a role in whether or to what extent a plantdecides to proceed with a recycling concept. It is worth mentioning here thatrecovery/reuse of both chemicals and water is different from that of only wa-ter, in that the former entails handling of the point sources separately, whilethe latter may be achieved by following usual end-of-pipe strategy (mixingdifferent streams).
A submerged microfiltration membrane bioreactor (MBR) implementinga mixed microbial culture predominantly composed of white-rot fungi con-stitutes the core of the proposed hybrid dye wastewater treatment scheme.The fungi MBR78 couples the excellent recalcitrant compound degradabilityof white-rot fungi with the inherent advantages of an MBR. To sustain an un-interrupted supply of nonspecific extra cellular enzyme by fungi, the reactorrequires operation under a quasi-controlled environment (acidic pH) withsimultaneous supply of an easily biodegradable carbon source (e.g., starchused in textile sizing). In the case of an integrated textile plant, after thechemical and water recoveries as indicated in Figure 2, the concentrates anddiscarded streams may be fed to the MBR. Depending on the case-specific
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362 F. I. Hai et al.
requirement, the MBR may be augmented by a subsequent advanced oxi-dation facility (e.g., solar photocatalysis187). An internal recycle strategy be-tween the MBR and the photoreactor may prove to be further beneficial.Depending on the site-specific quality achievement, the final effluent may bereused with or without mixing with fresh water. In the case of a plant deal-ing only with dyeing and finishing, however, a slightly changed approachof water and electrolyte recovery is recommended. In this case since otherstreams except the dyeing and finishing streams are absent, the concentratedreject stream generated after water and salt recovery from segregated dyebath effluent and rinse water cannot be diluted. Under this condition, thedye bath effluent and rinse water may be directly fed to the MBR–AOP se-quence, and then desalinated by membrane (RO/NF), with the concentrate(salt) and permeate (water) being reused.
Due to declining membrane costs,34 recovery and reuse of chemicalsand water using membranes is expected to gain rapid acceptability in nearfuture. The concentrates generated therefrom and discarded streams (includ-ing dye), however, entail further effective economical treatment. This maybe realized by an on site membrane separated fungi reactor. Requirementof small plant size is one of the inherent advantages of MBR process. Thefungi MBR,78 in addition, can achieve excellent effluent quality. Besides,posttreatment of the MBR permeate by an AOP will ensure complete de-coloration. Moreover, use of the AOP for posttreatment will minimize itslight penetration limitation, which would be significant if it were used forpretreatment. Last but not least, the approach of utilizing solar light for pho-tocatalysis adds to the effort to conserve energy sources. Based on this rea-soning, the proposed conceptual integrated treatment scheme appears to beattractive.
This article intends to underscore the indispensability of hybrid tech-nology for dye wastewater treatment and endorses the inclusion of energyand water reuse plan within the treatment scheme. However, the proposedlayout is certainly not claimed to be a panacea for textile dye wastewa-ter. It is rather a demonstration of one of the probable suitable combina-tions. In line with the broad spectrum of hybrid technologies portrayedin this article, some additions/modifications to the proposed scheme mayalso be considered. For instance, simultaneous addition of adsorbent in theMBR,189 utilization of concurrent AOP adsorption systems,91,132 etc. are worthexploring.
Other approaches may enjoy case-specific superiority over the proposedscheme. For example, with more advancement in the reactor design for AOPs,the partial preoxidation by AOP (may be combination among AOPs them-selves) prior to MBR treatment may appear to be more appropriate in nearfuture. Conversely, incineration/wet air oxidation of dye bath concentrate(possessing high calorific value34) remaining after material and water recov-ery by membrane may also furnish an attractive solution.
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Hybrid Treatment Systems for Dye Wastewater 363
7. CONCLUSION
Residual dyes along with other auxiliary chemical reagents used for process-ing, impurities from the raw materials, and other hazardous materials appliedin the finishing process impose massive load on wastewater treatment sys-tem. This eventually leads to a poor color and COD removal performance.The release of colored wastewater in the ecosystem is a remarkable sourceof esthetic pollution, eutrophication, and perturbations in aquatic life. Theseconcerns have led to new and/or stricter regulations concerning coloredwastewater discharges, rendering the decolorization process further difficultand costly. To combat this problem, researchers have put forward a widevariety of hybrid decolorization techniques. Based on the array of potentialhybrid technologies and the available cost information, it can be concludedthat hybrid technologies having biological processes as the core appear to bethe most prospective ones. It should also be emphasized here that inclusionof energy and water reuse plan within the treatment scheme is an imperative.In this context, membrane technology has an immense role to play. Mem-brane bioreactors implementing special dye-degrading microorganisms andinvolving simultaneous addition of adsorbent in MBR may surface as poten-tial contenders among present-day dye wastewater treatment processes. TheMBR technology may also be combined with advanced oxidation facilities.Case-specific selection of the appropriate hybrid technology is the key torealization of a feasible system.
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