Open Journal of Safety Science and Technology, 2011, 1, 12 -18
doi:10.4236/ojsst.2011.11002 Published Online June 2011 (
Copyright © 2011 SciRes. OJSST
Treatment of Dye Effluent by Electrochemical and
Biological Processes
Balakrishnan Ramesh Babu, Anand Kuber Parande*, Saravanan Arun Kumar,
Sirasanaganbla Udya Bhanu
Central Electrochemica l Research Institute, Karaikud i, India
E-mail: *
Received May 3, 2011; revised June 1, 2011; accepted June 7, 2011
Textile dye wastewater is well known to contain strong colour, high pH, temperature, Chemical Oxygen
Demand (COD) and biodegradable materials. The electrochemical treatment of wastewater is considered as
one of the advanced oxidation processes, potentially a powerful method of pollution control, offering high
removal efficiencies the removal of colour of methyl red azo dye is a challenge in textile industry. The fol-
lowing methods have been adopted for the treatment of real textile wastewater: 1) Electro-oxidation (EO)
and 2) Bio-treatment (BT). In EO process, reduction of COD and removal of colour were 70% and 81% re-
spectively. The effluent was further treated by BT. BT showed a final reduction of 92% of COD and removal
of colour by 95%. Both the combined processes were highly competitive and showed a very good reduction
of COD and colour removal. Electrochemical processes generally have lower temperature requirement than
those of other equivalent non-electrochemical treatments and there is no need for additional chemicals. These
treatment methods may also be employed successfully to treat other industrial effluents.
Keywords: Textile Wastewater, COD, Colour Removal, Electro Oxidation, Biological Process, FTIR
1. Introduction
Treatment of real textile wastewater (RTWW) has be-
come a real challenge in recent years. The textile indus-
try is one of the most important export industries of India.
The RTW is notoriously known to have strong color,
large amount of suspended solids (SS), broadly fluctuat-
ing pH, high temperature, and high Chemical Oxygen
Demand (COD) [1,2]. Different combinations of treat-
ment methods have been proposed in order to be effec-
tive. Removal techniques for coloring substances include
adsorption, precipitation; coagulation, filtration, and
chemical oxidation have been studied by many research-
ers [1-5].
Biological methods are generally cheap, simple and
easy to apply to remove organic compounds in the textile
wastewater [6-8]. But the refractory pollutants present in
the RTW cannot easily be degraded by traditional bio-
logical process with microorganisms [9,10]. It can be
treated by some other methods to make the effluent as
The use of anaerobic digestion for the decolorisation
of dyes has been investigated [11]. Textile dyes can
rarely be aerobically degraded; azo dyes can be anaero-
bically reduced, producing colorless aromatic amines. In
the first stage the dye is decolorized by the reduction of
the azo bond through bacteria directly or indirectly under
anaerobic conditions. In order to produce reduction
equivalents that can be transferred to the dye molecule,
an auxiliary substrate must be present that can be oxi-
dized by the bacteria [12-15]. Large polar sulfonated
dyes [16] such as reactive dyes are unlikely to diffuse
through the cell membrane, so that extra cellular non-
enzymatic redox mediators, e.g. chinones, play an im-
portant role in decolorization with whole cells [17].
Azo dyes are chemical compounds bearing the func-
tional group R–N=N–RO in which R and RO are aryl
groups. Because of the electron delocalization through
the N=N group these compounds have vivid colors, such
as red, orange, or yellow [18,19]. The colour is depend-
ent on the chromophore and the extent of conjugation.
Depending on the number of azo groups there are mono-,
di- and tri-azo dyes. Azo dyes generally are bound to the
textile fibres through secondary bonds. Reactive dyes
contain different organic compounds which forms a
chemical bond with textile fibers [20,21].
The electrochemical treatment of wastewater is con-
sidered as one of the advanced oxidation processes, po-
tentially a powerful method of pollution control, offering
high removal efficiencies. Electrochemical processes
generally have lower temperature requirement than those
of other equivalent non-electrochemical treatments and
there is no need for additional chemicals. The required
equipments and operations are simple. Their controls are
easy and the electrochemical reactors are compact. It can
also prevent the production of unwanted secondary
sludge. The main oxidizing agent in electrochemical
process is hypochlorite ion or hypochlorous acid gener-
ated produced from chloride ions.
Azo dyes constituting the largest class among the syn-
thetic colors. The effective and economic performance of
the process has been proven to be strongly dependent on
electrode materials, and many researchers have investi-
gated electrochemical oxidation for azo dye degradation
through operating parameters optimization using various
anodes including RuO2, SnO2, PbO2 and diamond elec-
trode [22-25].
Nowadays, many combined processes are suggested.
One of the studies reported that RTW was treated by the
combined processes of chemical coagulation, electro-
chemical oxidation and activated sludge [26]. Ahn et al.
[27] studied Fenton’s oxidation and activated carbon
adsorption as pretreatment processes for dyeing waste-
water treatment. Nicolaou and Hadjivassilis [28] em-
ployed the combined process of chemical coagulation,
activated sludge filtration and disinfection for textile
wastewater treatment. The present study emphases a
method for the removal of COD and colour from RTW
contains methyl red azo dye by the application of EO and
followed by BT.
2. Materials and Method
All the reagents used were of AR grade.
The azo dye used in this study was obtained from a
textile-dyeing factory located in Tirupur, Tamil Nadu,
India. The characteristic of RTWW is shown in Table 1.
Biodegradation was carried out at a temperature of 25˚C
in 250 ml flasks. Table 2 shows the composition of the
Textile Wastewater (RTWW)
2.1. Experimental Setup for EO Process
The schematic diagram of the experimental setup given
in Figure 1 consists of a glass beaker of 500 ml capacity
with PVC lid having provision to fit a cathode and an
anode. Salt bridge with reference electrode was inserted
through provided in the lid. Proper provisions were made
in the lid for inserting of thermometer and for periodic
Table 1. Characteristics of textile wastewater.
S.No.Parameter Range
1. pH 11.4
2. Temperature (˚C) 32
3. COD (mg/L) 8060
4. Suspended solid (mg/L) 270
5. Conductivity (mho/cm) 2800
6. Chlorides (mg/L) 160
Table 2. The composition of the Textile Waste water.
S NoWater Characteristics : Concentrations
1 colour Dark reddish orange
2 turbidity 1026 NTU
3 pH 8.62
4 Chemical Oxygen Demand (COD) 3145 mg/L
5 Total Suspended Solids 836
6 Conductivity 4500
7 Dissolved Oxygen 1.1 mg/L
Figure 1. Schematic diagram of the experimental setup for
EO process.
sampling. It comprises of an anode, a cathode and DC
rectifier. The anode was made of mesh of titanium (12
cm × 6 cm) coated with RuO2, stainless steel (12 cm × 6
cm) was used as cathode. The distance between elec-
trodes was 1.5 cm. The applied current density was 2
A/dm2 and 400 ml of biologically treated combined dye
house wastewater was taken in the glass beaker for fur-
ther reduction of COD by electro oxidation. Experiments
were carried out under galvanostatic conditions using a
DC-regulated power source (HIL model 3161) of 0 - 2 A
Copyright © 2011 SciRes. OJSST
14 B. R. BABU ET AL.
and 0 - 30 V. Stirring was done with a magnetic stirrer.
Electrolysis was carried out under batch mode. During
these processes samples were collected at different time
intervals and the COD was measured. Standard methods
for examination of wastewater [29] were used for the
estimation of COD and colour.
2.2. Enumeration of Micro Organism
The textile sample was serially diluted using 9 ml dis-
tilled water blanks. The total viable counts were enumer-
ated using nutrient agar medium by pour plate method
[30]. Duplicate samples were tested along with control.
Total viable counts were made based on the following
2Average number of colony10 ml
CFU/cm Dilution factorvolume of sample added
2.3. Analytical Measurements
FTIR and UV techniques were adopted for analysis of
treated and untreated dye effluent by EO and BT.
3. Results and Discussion
3.1. Electro-Oxidation Process
Table 3 and Table 4 shows that values of reduction in
COD as well as colour. About 70% of COD removal and
80% of colour removal was achieved by this method. The
mechanism of electrooxidation is explained in Figure 2.
3.2. Mechanism of Electro Oxidation
In known that the organic compounds are completely
oxidized to carbon dioxide. The electrode materials with
high electro catalytic the complex organic compounds to
its simple fragments than can be easily oxidized to car-
bon dioxide and water so as to split activity the organic
compounds are degraded to CO2 and H2O.
In case of EO, OH, generated electrochemically by
splitting of H2O, gets discharged at the anode resulting in
radical (OH) as shown in Equation (1)
22 2
 
Later, the (OH) radical, gets adsorbed on to the RuO2
forming a complex of the type (RuO2(OH)) which inturn
gets converted to (RuO2(O)) of higher oxidation state.
 
 
Thus both physisorbed (RuO2(OH)) active oxygen and
Table 3. Effect of current density on the treatment of efflu-
ent by electro-oxidation process.
Final COD (mg/l) (5 hours)
Current density (A/dm2)
Initial COD
1 1.5 2 2.5
8060 2805 2964 2430 2458
Table 4. Treatment of textile effluent by Biological Treat-
ment method.
Biological Treatment
COD (mg/l)
Name of the
Organism Initial Final
(5 days)
% Reduction
of COD
% Reduction
of colour
putida 2430 215 91.15 95.23
chrysosporium 2430 350 85.59 93.02
cereus 2430 455 81.27 90.27
virdae 2430 540 77.77 85.16
Figure 2. Structure of Methyl red azo dye.
chemisorbed (RuO2(O)) active oxygen release diatomic-
oxygen. It can be considered that at the anode surface
two states of “active oxygen” can be presented:
RuOORuO1 2O
It may be speculated in this case that physisorbed ac-
tive oxygen predominantly oxidized the organics and
chemisorbed oxygen RuO2(O) decides the fate of the
intermediate product.
3.3. Biological Process
More than 20 microbes were isolated from the textile
wastewater. Four microbes namely Pseudomonas, phan-
erochaete, Bacillus and tricoderma were used in this
Copyright © 2011 SciRes. OJSST
Copyright © 2011 SciRes. OJSST
study. The microbes culture were cultivated in a fer-
menter containing sterilized media, nutrient broth, and
utilized to inoculate into wastewater. The COD reduction
by the biological treatment was carried out. Table 3
shows COD removal efficiency. At the end of 5th day,
Pseudomonas putida gives the maximum reduction of
COD as 92% and colour removal as 95% respectively.
concluded that by the action of hydrolysis microbes, azo
in raw waste water produced organic amine and NH3 and
these product solutions were alkaline, the quantities of
organic amine and NH3 augmented gradually.
3.5. Mechanism of Azo Dye Reduction
The very first step in the bacterial degradation of azo
dyes, in both the anaerobic or aerobic conditions, is the
reduction of the –NN– bond. This reduction might be
involving different mechanisms. For example the reac-
tions of the enzymes, low molecular weight redox me-
diators, chemical reduction by biogenic reductants like
sulfide or a combination which is shown in the Figure 3.
Additionally, the location of the reactions can be either
intracellular or extracellular depending on the availabil-
ity of the active microbial species.
3.4. Mechanism of Pseudomonas Putida in
Among the microbes, the addition of Pseudomonas
putida into the RTWW gave the best performance in the
reduction of COD. Aromatic compounds are susceptible
to biological degradation in both aerobic and anaerobic
conditions. Diazo bond in azo dyes could be parted by
azo reductive enzyme produced by Pseudomonas putida
in anoxic or anaerobic condition, and then an azo dye
molecule was made of two amine molecules holding
–NH2 [31].
12 122
Microorganisms, bacteria, with their enzyme systems
degrade the aromatic structure under aerobic and anoxic
conditions [33-34]. However, in both the conditions,
microbes metabolize aromatic compounds in both the
peripheral and central path-ways of the cell [35]. Periph-
eral pathways convert a wide variety of compounds into
a few intermediate products or fragments. In aerobic
metabolism, the initial reactions involve the replacement
of other functional groups attached to the aromatic ring
with hydroxyl groups, followed by cleavage by involving
where R1 and R2 were various phenol and naphthol resi-
dues. Then after, amine could be decomposed by ammo-
nia by an action of hydrogenation enzyme and hydrolysis
enzyme in anoxic condition [32]. From the study it is
Figure 3. Schematic representation of different mechanisms of anaerobic azo dye reduction. RM = Redox mediator; ED =
lectron donor; b = bacteria(enzymes). e
Copyright © 2011 SciRes. OJSST
two oxygen atoms. These reactions are catalysed by
enxymes like hydroxylases and oxygenases. Under an-
oxic conditions ring reduction and other unique reactions
such as carboxylation, reductive dehydroxylation, addi-
tion reactions etc are predominant which are absent in
the aerobic metabolism [35].
The trend of the microorganism in removal of COD
and colour is as follows:
Pseudomonas > phanerochaete > Bacillus > Tri-
3.6. FTIR Analysis of the Sample
The sample was given for FTIR spectrum analysis before
and after treatment. Figure 4 shows the FTIR spectra of
untreated and treated by electrooxidation and biological
method dye effluent. Major peaks were obtained for un-
treated sample at 3302.08, 2107.55, 1636.47 and 709.29
cm1 shown in Figure 4(a). The absorbance of peaks at
3302.03 cm1 and 1636.47 cm1 were due to the structural
vibration of hydrogen in bound with OH groups of phenol
or OH of carboxyl groups COOH and the hydrogen vi-
bration of amide N-H functions. It shows that the sample
contain high content of water molecule and considerable
amount of alkanes (CH). After decolourization showed
absence of peak at 1600 cm1 indicates breakdown of azo
bond, might be due to action of azo reductase. Absence of
peaks at 688 cm1, 726 cm1, 765 cm1 and 827 cm1 in-
dicates loss of aromatic or benzene ring.
The absorbance of peaks at 2107.99 cm1 was due to
the vibration of C=O and intense absorbance of the bands
at 1620 - 1640 and 1510 - 1540 cm1 was also observed,
indicating enrichment in amide and aromatic. The ap-
pearance of peak at 1636.47 cm1 indicates the pressure
of C=C conjugated diene groups. This is due to the func-
tional group of aromatic carbons. The absorbance of
peaks at 709.23 cm1 (out-of plane bending modes of
aromatic CH bonds) was found to be due to the vibra-
tion of aromatic compounds and benzene ring. Figure
4(b) shows the FTIR spectra of treated sample by Elec-
tro-Oxidation. After the EO method, decolourization
showed absence of peak at 1636.47 cm1 indicates
breakdown of aromatic rings. Peak at 1615 cm1 indi-
cates synthesis of aliphatic secondary amines and di-
methyl groups it seems that azo reductase catalyses the
reductive cleavage of the azo bond of methyl red [36].
Figure 4(c) shows the FTIR spectra of biologically
treated sample. Out of the four organisms used Pseudo-
monas putida showed the best performance which de-
grades to facilitate by oxidative enzymes.
3.7. UV
The samples were given for UV–Vis spectra analysis
before treatment and after EO treatment and BT treat-
ment and are shown in Figure 5. The intensity of peaks
was reduced by EO and is shown in Figure 5(b) and
followed by BT method Figure 5(c). The dye UV spec-
trum before treatment exhibited absorption bands at 545
nm. The characteristic band at 485 to 570 nm could be
assigned to the n-* transition of –N=N– group [37]. The
weak band below 350 nm could be attributed to the -*
transition related to the aromatic ring attached to the
–N=N– group in the dye molecule. It is apparent that the
intensity of characteristic band (545 nm) of dye solution
was found to diminish gradually during the experiment
and disappeared totally after EO and BT. The disappear-
ance of the bands indicates the effective destruction of
the azo. The intensity of the absorption spectra was re-
duced further by BT as it is evident from Figure 5(b)
when compared with EO treatment shown in Figure 5(c).
It could be concluded that the dye molecule undergoes
degradation in the presence of microorganisms. This
clearly indicates that the intensity of the absorption spec-
Figure 4. FTIR spectra of untreated dye effluent (a), elec-
tro-oxidation (b) and biologically treated (c).
Figure 5. UV–vis spectra of untreated dye effluent (a), elec-
tro oxidation (b) and biologically treated (c).
usions were drawn:
ficantly by elec-
ld, F. Judkins and B. L. Weand, “Process
Chemistry for Water and Wastewater Treatment,” Pren-
ol. 35,
tra was reduced drastically after the combined effect of
both the treatments.
4. Conclusions
The following concl
1) COD and colour were reduced signi
trooxidation followed by biological method and the
maximum were obtained as 91% and 95% respectively.
2) Pseudomonas putida showed the best bacteria for
the reduction of COD and colour.
3) The performance of colour removal was signifi-
cantly improved by the application of the combined
treatment methods which was observed in UV studies.
4) FTIR reveals that aromatic compounds degraded to
aliphatic compounds which are easily biodegradable.
5) The treated water can be reused for effective dyeing
6) The intensity of UV–Vis spectra was reduced dras-
tically that clearly indicates azo dye degradation with
electro-oxidation followed by biological treatment.
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