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Journal of Chemical Technology and Biotechnology J Chem Technol
Biotechnol 78:1219 1224 (online: 2003)DOI: 10.1002/jctb.924
Direct filtration of Procion dye bathwastewaters by
nanofiltration membranes:
flux and removal characteristicsIsmail KoyuncuIstanbul Technical
University, Faculty of Civil Engineering, Department of
Environmental Engineering, 80626, Maslak, Istanbul, Turkey
Abstract: The treatment and reuse of industrial wastewaters by
membrane processes has become more
attractive in the last few years due to constraints on water
usage. The aim of this study was to investigate
the direct filtration of reactive dye house wastewaters by
nanofiltration membranes based on permeate
flux, and sodium chloride and colour removal. Experiments were
performed using both synthetic and
industrial dye bath wastewaters with the fluxes of the
industrial dye bath wastewaters lower than those
of the synthetic solutions. The effects of operating conditions
such as pressure and pH were assessed.
Studies with DS5 DK type (polysulfonepolyamide) membranes showed
that nanofiltration membranes
are suitable for direct treatment of wastewaters and the
permeate quality was appropriate for reuse in the
dyeing process. Pre-treatment and neutralisation were important
for recovery of large amounts of salt
and water from the permeate stream. Neutralisation of the
solution with HCl rather than H2SO4 gave a
better permeate from the point of view of the reuse. The highest
permeate flux and colour removal and
the lowest salt removal were achieved with the HCl
neutralisation.
2003 Society of Chemical Industry
Keywords: nanofiltration; neutralisation; reactive dye; membrane
fouling; NaCl recovery
INTRODUCTION
As groundwater levels decrease and industrial water
prices increase, there is an emphasis on identifying and
investing in new water sources for future demands.
Such alternative processes include desalination of
brackish and sea water, and the reclamation and reuse
of wastewaters. Several new unit processes for water
and wastewater treatment such as membrane technol-
ogy have been used in desalination and reclamation of
both municipal and industrial wastewaters.1,2
The textile industry is an important industry in
Turkey. Large amounts of water are used and huge
amounts of wastewater are produced at the same
time. The effluents from reactive dye baths are
highly-coloured streams containing hydrolysed dye
together with auxiliary chemicals.3 Thus, wastewaterreclamation
in this industry is highly desirable because
of the opportunities to reduce both the volumes
of wastewater produced and the water consumed.
Membrane processes can be used for the purification
of these complex wastewater streams.412
Nanofiltration membranes show great potential for
direct reuse of dye bath wastewaters in the textile
industry. While water and sodium chloride pass
through the membrane, most of the divalent ions
and dye molecules can be rejected. There have been a
number of reported studies on textile dye bath waste-
water treatment with nanofiltration membranes.711
Direct filtration of dye baths containing reactive dyes
without dilution by rinsing water and without pre-
treatment, has been evaluated to separate sodium
chloride from dye baths by nanofiltration membranes
in tubular modules.8 After nanofiltration of simulated
wastewaters, 99% colour removal and 84% salt
recovery were achieved. Thus, the direct nanofiltration
of dye bath wastewaters has been shown to be a realistic
method for treatment of textile industry wastewater as
well as activated sludge effluent.12 The decline in
the permeate flux was fully reversible and reached
a stable value in all studies. The performance of
nanofiltration membranes can be improved by either
changing the chemical composition of the membrane,or modifying
the membrane surface by varying the
activation time and concentration of the activating
agent.13 Separation factors for different reactive dyes
of greater than 98.5% have been achieved using
nanofiltration membranes.14
The most important parameters in economic terms
for the direct reuse of dye bath wastewaters are
the flux and the recovery rate of sodium chloride.
Consequently, current studies have been orientated
to maximise these parameters. This paper presents
Correspondence to: Ismail Koyuncu, Istanbul Technical
University, Faculty of Civil Engineering, Department of
Environmental Engineering,80626, Maslak, Istanbul, Turkey
E-mail: [email protected]
(Received 17 September 2002; revised version received 3 February
2003; accepted 1 August 2003)
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the comparative evaluation of the results from both
synthetic and actual reactive dye bath wastewaters
based on permeate flux, sodium chloride recovery and
colour removal.
EXPERIMENTAL
ApparatusThe Sepa CF laboratory-scale 316SS membrane cell
was supplied by Osmonics Inc and was as described
in previous work.15 The feed vessel volume was about
50dm3. The experimental system had two pumps: a
low pressure and a high pressure pump operating in
series so that the low pressure pump supplied sufficient
inlet pressure for the high pressure pump. The high
pressure pump was able to supply a feed pressure up to
10 000 kPa and a feed flow rate up to 1000 dm3 h1. A
rotameter was provided to measure the feed flow rate
up-stream of the membrane cell. Also, pressure gauges
were used to measure the inlet and outlet pressures.
Allexperiments were carried out at constant temperature
of 25 1 C and constant cross flow velocity of
0.74ms1. Constant temperature was also supplied
by using a heat exchanger in the feed tank (Fig 1).
The concentrate stream was returned to the feed vessel
while the permeate stream was collected separately. A
cartridge filter (10m pore size) was used as a pre-
filter to remove coarse particulates from the dye bath
wastewater prior to nanofiltration. A DS5 DK type
(polysulfone polyamide) nanofiltration membrane
(0.0155 m2) with an approximate molecular weight
cut-off of 150 300 Da, supplied by Osmonics as a flat
sheet, was used in this study.
Table 1. The wastewater composition of the synthetic and
industrial
Procion dye baths
Component
Concentrations
(gdm3)
in synthetic
wastewater
Concentrations
(gdm3)
in industrial
wastewater
Reactive Navy HEXL (RN) 0.2 0.2
Reactive Blue HEGN (RB) 0.2
Reactive Crimson HEXL (RC) 0.04
NaCl 30 30
Na2CO3 15 15
Acetic acid 0.3 0.3
Verolan NBO 0.5 0.5
Slipper 1 1
Wastewater composition
The Procion dye bath, containing high concentrations
of NaCl, was simulated for the initial experiments.The
composition of the Procion dye bath from the
local cotton textile industry is given in Table 1. The
simulated Procion dye bath solutions were prepared
step-wise by adding the auxiliary chemicals in five
stages (Table 2). It was considered that, for the
preparation of the synthetic dye bath, approximately
20% of the dyes and 100% of all other chemicals
remained in the exhausted dye bath wastewater.16
Reactive Navy HEXL (RN) used in the synthetic
solutions was supplied by the local textile company.
NaCl, Reactive Navy HEXL, Na2CO3, acetic acid,
Slipper (Mega Tec Company) and Verolan NBO
(Rudolf Duraner Company) were added to the
Low pressurepump
Prefilter
Flowmeter
High pressurepump
Cell holder
Back pressure valve
Coolingsystem
(Tapwater)
Concentrateflow
Manometer
Feed Vessel
Computer
Permeate
Balance
Manometer
Cell body
Piston clampingmechanism
Temperaturecontroller
Manometer
Figure 1. Schematic flow diagram of the laboratory membrane
system.
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Direct filtration of Procion dye bath wastewaters
Table 2. The composition of simulated wastewaters prepared
step-wise in five stages
Stage no Solutions
1 Distilled water
2 NaCl
3 NaCl + Reactive Navy HEXL (RN)
4 (a) NaCl + Reactive Navy HEXL (RN) +Na2CO3 (pH = 10.5
(original pH))
4 (b) NaCl + Reactive Navy HEXL (RN) +Na2CO3 (pH = 7 with
HCl)
5 (a) NaCl + Reactive Navy HEXL (RN) +Na2CO3 + acetic acid
+Verolan NBO (ion keeper)+ Slipper (broken preventer)
(pH = 10.5 (original pH))
5 (b) NaCl + Reactive Navy HEXL (RN) +Na2CO3 + acetic acid
+Verolan NBO (ion keeper)+ Slipper (broken preventer)
(pH = 7 with HCl)
synthetic dye baths. Slipper is manufactured by micro-
dispersion of polyester co-polymers and used to
prevent fibre damage, which minimises the friction
between metals and fibre. The pH of the solution is
9.5 for the 10% slipper solution. The other auxiliary
chemical, Verolan NBO, contains polyacrylate and
alkaline phosphonate, and retains some ions such as
iron from the fibre surface; the pH of the solution is
5 for the 5% Verolan NBO solution. Reactive Blue
HEGN (0.2 g dm3) and Reactive Crimson HEXL
(0.04gdm3) were also used in the actual industrial
dye bath preparation. All synthetic solutions were
prepared using distilled water. Since the pH value
required adjustment to neutral pH values for the
reuse of permeates in the actual process,12,17 the
effluent was neutralised before nanofiltration with
either 0.1 mol dm3 HCl or 0.01moldm3 H2SO4solutions.
Analytical methods
The colours of the feed and permeate samples were
analysed with a Spectronic 20D spectro-photometer
at a wavelength of 595 nm which is the maximum
absorbance. An ORION SA 720 type pH meter was
used to measure pH. An AGB-1001 Laboratory Data
Logging system was used to monitor temperature
and conductivity. The concentration of chloride
was determined by potentiometric titration using
0.1 mol dm3 AgNO3. All parameters were recorded
for the feed and permeate flows. Process performance
was evaluated by the permeate flux, removal of
salt and colour, and the pressure at the inlet andoutlet of the
module during each experiment. The
permeate flux was determined gravimetrically with
the data logging system as shown in Fig 1, and the
permeate conductivity and flux values were used to
determine when the permeate composition and flux
had reached steady state after changing the applied
pressure. The removal efficiency is calculated using
the following equation:
R(%) =
1
Cp
Cf
100 (1)
where Cf is feed water concentration and Cp is
permeate water concentration.
RESULTS AND DISCUSSION
Studies with synthetic dye bath wastewaters
The composition of the synthetic Procion dye bath
is given in Table 1. Experiments were conducted in
five stages (Table 2) to understand the effects of salts,
dyes and auxiliary chemicals on membrane fouling,
and salt and colour removal. In the first step, distilled
water experiments were performed to determine the
pure water flux rate for the DS5 DK membrane.
NaCl solution (30 g dm3) was used in the second
step. In the third stage, Reactive Navy HEXL (RN)
(0.2gdm3) was mixed with the NaCl solution. The
pH value of the feed solution during the first three steps
was about 7. With the addition of 15 g dm3 Na2CO3solution in the
fourth step, however the pH value
increased to 10.5, typical for dye bath wastewaters.
Experiments were carried out with wastewaters at the
original pH and following neutralisation with HCl in
the fourth step. Finally, in the fifth step acetic acid,
Verolan NBO and Slipper, and the other additivesin the dye bath,
were added to the solution. The
pH value of the feed solutions at this stage was
10.5 and 0.1 mol dm3 HCl was used to neutralise
the feed solution before nanofiltration. Pressures of
800 2400 kPa were applied and the flow velocity was
set at 0.74 m s1. Flux values of the membrane system
were determined using the data logging system.
Figure 2 shows the steady state flux values, after
2 h operation, versus pressure with respect to the
simulated dye bath solutions for these five steps.
0
10
20
30
40
50
60
70
80
90
100110
0 5 10 15 20 25 30
Pressure, kPa ( 100 )
Flux,dm
3m
-2h
-1
1) Distilled water2) NaCl
3) NaCl+RN4) a) NaCl+RN+Na2CO3
b) NaCl+RN+Na2CO35) a) All chemicals
b) All chemicals
Figure 2. Flux versus pressure graphs for the synthetic
wastewater
experiments. (a) Original pH; (b) HCl-neutralisation.
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Permeate conductivity and flux values were also used
to monitor when the permeate composition and flux
reached constant values after changing the applied
pressure.18 The permeate flux (Jv) increased with
increasing pressure for the five steps (Fig 2) with
the highest flux, about 110 dm3 m2 h1 at 2400 kPa,
achieved for distilled water (step 1). The fluxes
decreased, however, with the addition of componentsto the dye
bath. Thus a flux of 73 dm3 m2 h1 was
obtained at 2400 kPa for the 30 g dm3 NaCl solution,
and addition of 0.2 g dm3 Reactive Navy HEXL (RN)
further slightly affected the flux. In addition, there
was a greater influence on membrane fouling with
the addition of 15 g dm3 Na2CO3 because of the
high pH of the solution. The effect of pH can be
explained by dye aggregation and the related influence
on dye hydrophobicity. Under alkaline conditions, the
formation of a strong and stable dye salt complex
will result in an increase in dye hydrophobicity.19
Therefore, the adsorption of dye molecules on themembrane
surface increases under alkaline conditions,
resulting in fouling of the membrane surface giving
a flux value at pH 10.5 of about 34dm3 m2 h1
at 2400 kPa. To investigate the effect of pH at this
stage, the pH of the solution was decreased to 7
using 0.1 mol dm3 HCl. After this adjustment the flux
increased to about 63.5 dm3 m2 h1 at the pressure of
2400 kPa, probably due to the decreasing effect of dye
hydrophobicity at the membrane surface. Acetic acid,
Verolan NBO and Slipper, and the other additives,
were added to the solution in the last stage with
similar results to step 4. The first run (5a) was carriedout at
pH 10.5. As seen from Fig 2, the flux of this run
was about 52.5 dm3 m2 h1, however, this increased
to 70dm3 m2 h1 for the second run (5b) conducted
with the solution neutralised using 0.1 mol dm3 HCl.
The effect of pressure on salt removal was evaluated
in stages 2 5. Removal efficiencies were calculated
by determining the Cl ion concentrations in the
feed and permeate streams. Low NaCl removal
was important for NaCl recovery in the permeate
stream. The higher the NaCl concentration in the
permeate, the lower would be the NaCl demand in
the preparation of subsequent dye baths. As shown
in Fig 3, Cl rejections increased with increasing
pressure in all experiments. The highest Cl rejection
of about 44% at the pressure of 2400 kPa was
observed with 30 g dm3 NaCl. Addition of 0.2 g dm3
Reactive Navy HEXL (RN) had a slight effect on
Cl rejection. In step 3, however the addition of
15gdm3 Na2CO3, probably because of the resulting
increase in osmotic pressure, gave the largest effect
on salt removal. Subsequently neutralisation with
0.1 mol dm3 HCl further decreased the Cl rejection.
Increase in the NaCl concentration in the feed,
together with the addition of HCl, further decreased
the osmotic pressure differences in the feed and
permeate due to the contribution of HCl to the overall
Cl concentration. Similar results were also obtained
0
0.1
0.2
0.3
0.4
0.5
0 5 10 15 20 25 30
Pressure, kPa ( 100 )
RsOBS,%(
100)
2) NaCl3) NaCl+RN4) a) NaCl+RN+Na2CO3
b) NaCl+RN+Na2CO35) a) All chemicals
b) All chemicals
Figure 3. Salt removal versus pressure graphs for the
synthetic
wastewater experiments. (a) Original pH; (b)
HCl-neutralisation.
in the final stage. The lowest Cl rejection of 27% was
achieved with the neutralised solution.
Colour removal was also determined using simu-
lated dye bath effluents by analysis at the maximum
absorbance of the dye at 595 nm; the permeate was
almost colourless. The highest colour removal (>99
%) was achieved with the solution neutralised with
0.1 mol dm3 HCl while the lowest colour removal was
obtained in the first step with the mixture of 0.2 g dm3
Reactive Navy HEXL (RN) and 30 g dm3 NaCl.
Studies with industrial dye bath wastewaters
Industrial dye bath wastewater samples (Table 1) were
taken from a local textile company in the province of
Istanbul, Turkey. Experiments were performed under
similar operating conditions to those used for synthetic
wastewater experiments. The pH value of the original
wastewater was about 10.35 and 0.1 moldm3 HCl
and 0.01 mol dm3 H2SO4 were used to neutralise the
feed solutions before nanofiltration. The performance
of the membranes was evaluated by permeate flux, and
salt and colour removals at various pressures and pH
values.
The relationships between flux and pressure in
distilled water and dye bath wastewater experiments
at different pH values are given in Fig 4. All the
flux values were taken under steady state conditions.
0
10
20
30
40
50
60
70
80
90
100
110
0 5 10 15 20 25 30
Pressure, kPa ( 100 )
Flux,dm
3m
-2h-1
Distilled water
pH=10.35 (Original)pH=7 (with H2SO4)
pH=7 (with HCl)
Figure 4. Flux versus pressure for the industrial dye bath
wastewater
experiments.
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Direct filtration of Procion dye bath wastewaters
As with the synthetic wastewater experiments, feed
solutions were neutralised with 0.1 mol dm3 HCl
and 0.01 mol dm3 H2SO4. The permeate flux (Jv)
increased with increasing pressure for all experiments.
The fluxes for the industrial dye bath wastewater were
lower than for the synthetic wastewaters. This was
probably the result of particulate materials present in
the industrial wastewater. Flux values for the originalsolution
and neutralised solution with HCl decreased
by about 28% and 23% respectively compared with the
results of synthetic wastewaters. The lowest flux value
of 37.5dm3 m2 h1 was obtained with the original
solution. The highest flux value of 54 dm3 m2 h1,
however, was obtained with the neutralised solution
by using 0.1 mol dm3 HCl. Flux values for the
solution neutralised with 0.01 mol dm3 H2SO4 were
about 47dm3 m2 h1. It was slightly lower than
that for the solution neutralised with HCl. These
low flux values at high pH were probably the
consequence of the hydrophobicity of dye molecules
at the membrane surface. Furthermore, sulfate ions
in solutions neutralised with H2SO4 increased the
osmotic pressure of the feed and this caused lower flux
values for the solutions neutralised with H2SO4 than
with HCl.
Chloride ion removal was also determined for the
industrial wastewaters. Similar to the flux values, salt
removal from industrial wastewater was lower than
from the synthetic solutions with chloride rejection
from the original solution of about 28% at 2400 kPa.
There were small differences in Cl removal between
experiments conducted with the original solution and
the solution neutralised with H2SO4. The lowest Cl
removal, about 15% at 2400 kPa, was observed with
the solution neutralised with HCl (Fig 5). While the
feed Cl concentration increased with the addition of
0.1 mol dm3 HCl, the osmotic pressure differences
between the feed and permeate decreased further. It
can therefore be concluded that HCl-neutralisation
increased NaCl recovery.
A basic economic evaluation has been carried out
to estimate the annual income from the reuse of
NaCl. Permeate NaCl concentration is estimated as
25.5gdm3 based on 15% salt removal at 2400 kPa
0
0.1
0.2
0.3
0.4
0.5
0 5 10 15 20 25 30
Pressure, kPa ( 100 )
RsOBS,%(
100)
pH=10.35 (Original)pH=7 (with H2SO4)pH=7 (with HCl)
Figure 5. Salt removal versus pressure for the industrial dye
bath
wastewater experiments.
for the industrial wastewaters. With this concentration
and the NaCl unit cost of 0.041 $ per kg, the annual
income from NaCl reuse will be about $75 000 for
200m3 day1 capacity. From this basic calculation the
pay back period for the nanofiltration plant will be
about 2 years assuming a capital cost of $150 000.
Additional financial benefits from water and energy
reuse can decrease this pay back period. In addition,the NaCl
content of the reactive dye houses varies
between 20 and 80 g dm3 and all the different dye
wastewaters will be collected together and treated by
the nanofiltration plant. Therefore the salt content
of the feed solution will increase to an average value
of 40gdm3, and can decease the salt removal to
10%.9,17 In addition, the rate of salt removal can
further be lowered in real operation because of the high
recovery rate. Thus, overall, the use of a nanofiltration
plant to treat reactive dye wastewaters is an attractive
proposition.
CONCLUSIONS
The results of this study confirm previous observations
that nanofiltration is suitable for the direct treatment
of industrial wastewaters. Permeate quality was
appropriate for the reuse of the permeate in the dyeing
process. Nevertheless, further experiments should be
performed to study the effect of reuse of water on the
dyeing process. Pre-treatment and neutralisation were
important parameters for recovery of high amounts of
salt and water from the permeate stream. The results
from industrial dye bath experiments were differentfrom the
results of the synthetic experiments. The
fluxes of the industrial wastewaters were lower than
the synthetic solutions, and cartridge filtration had to
be used before nanofiltration to remove particulate
material. Experiments also showed that neutralisation
with HCl rather than H2SO4 gave better permeate
quality with respect to reuse, with the highest flux
and colour removal and the lowest salt removal. Basic
economic evaluation showed a pay back period for the
nanofiltration plant to be less than 2 years.
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