recovery of cr(iii) from tanning process using membrane separation processes

ORIGINAL PAPER

Recovery of Cr(III) from tanning process using membraneseparation processes

Berna Kiril Mert • Kadir Kestioglu

Received: 10 September 2013 / Accepted: 3 March 2014

� Springer-Verlag Berlin Heidelberg 2014

Abstract In chrome tanning wastewater study, a waste-

water treatment alternative was decided. This treatment

alternative contains cartridge filter, ultrafiltration [UF1

(20 kDa), UF2 (50 kDa), UF3 (150 kDa)], nanofiltration

NF (XN45), and reverse osmosis RO (ACM2). Chrome

tanning wastewater was given to the other membranes to

increase the life time of the membranes after cartridge filter

application. The wastewater from cartridge filter was given

to 3 different UF membranes which have different pore

diameters (20, 50, and 150 kDa) with 3 different pressure

(6, 8, and 10 bar) in this alternative. For this treatment

alternative, for 200 m3/G flow, 8 pieces of (273 m2) UF

(20 kDa), 8 pieces of (160 m2) NF (XN45), and 12 pieces

of (375 m2) RO (ACM2) membranes were used. The total

investment for this treatment alternative was calculated as

228,415 €, and process cost was calculated as 2.77 €/m3;

however, for the classical treatment facility, investment

was calculated as 345,400 €, and process cost was calcu-

lated as 0.8 €/m3. As a result when compared to classical

treatment systems, the membrane technology was found to

have more economic the investment and the process costs.

Keywords Ultrafiltration � Nanofiltration � Reverse

osmosis � Cr(III) � Cost

Introduction

Leather tanning is one of the most important industries in

Mediterranean as their complex wastewater characteristics;

leather tanneries are generally located in so called orga-

nized industrial districts (Lofrano et al. 2013).

Chrome tanning is one of the most popular tanning

systems in leather industry. Its versatility is well-known; it

offers excellent hydrothermal stability, better dyeing

characteristics, and softness to the leather (Kanagaraj et al.

2008).

The untreated release of tannery effluents containing

high COD, BOD levels, trivalent chromium, sulfides,

sodium chloride, Ca, Mg, organics and other toxic ingre-

dients effect flora and fauna of the ecosystem and increase

health risk of human being (Sundar et al. 2013).

Tannery chromium effluents are strictly regulated for

their alleged environmental consequences. Discharge limits

for trivalent chromium vary, broadly ranging from 1 to

5 mg/l in the case of direct discharge into water bodies

and from 1 to 20 mg/l in the case of discharge into the

public sewer systems. The level of chrome fixation on

processed hides/skins is still low enough to result in high-

economic loss, with close to 70 % uptake only achievable

in improved conventional tanning. The remaining 30 % of

basic chromium sulfate applied is left in the spent chrome

liquor and often wasted with the effluent (Tadesse et al.

2006).

There are many processes for the treatment of tannery

wastewater such as chemical coagulation (Lofrano et al.

2006), membrane processes (Gomes et al. 2010),

advanced oxidation (Modenes et al. 2012), adsorption

(Fabbricino et al. 2013), biological treatment (Mannucci

et al. 2010), electrocoagulation (Sengil et al. 2009), and

ion exchange (Sahua et al. 2009).

B. Kiril Mert (&)

Department of Environmental Engineering, Faculty

of Engineering, Sakarya University, 54187 Esentepe, Sakarya,

Turkey

e-mail: [email protected]

K. Kestioglu

Department of Environmental Engineering, Faculty

of Engineering and Architecture, Uludag University,

16059 Gorukle, Bursa, Turkey

123

Clean Techn Environ Policy

DOI 10.1007/s10098-014-0737-4

Chromium recovery’s traditional method is the precip-

itation of chromium salt with NaOH and the dissolution of

Cr(OH)3 in sulfuric acid. But, the quality of the solutions

which are recovered is not always optimal due to the pre-

sence of metals, lipidic substances, and other impurities. As

alternative method, membrane process is analyzed to

improve the quality of the recycled chromium (Das et al.

2006).

Treatment of the chromium rich tanning effluents using

UF and NF is mostly studied for the recovery and reuse of

tanning chemicals (Purkait et al. 2009). Another study

proposed a dual-stage treatment involving ceramic micro-

filtration (MF) followed by reverse osmosis (RO) com-

pared to conventional process. The final water was fit for

reuse in the tanning process (Bhattacharya et al. 2013).

Taleb-Ahmed et al. (2004, 2006) proposed the combination

of a physicochemical treatment and nanofiltration to

eliminate chromium from the tanning wastewater. Fabiani

et al. (1996) used a coupled-MF inorganic membrane as a

pre-treatment of the waste solution followed by an UF

polysulfone membrane to produce a clean chromium

solution (permeate) with 28 % recovery. Hafez and El-

Manharawy (2004) studied the reuse of chromium tanning

spent liquor low-pressure RO membranes. These authors

proposed a two-stage/two-pass system for chromium

removal and recovery.

Cassano et al. (2001, 2007) presented the possibility of

application of various membrane separation processes, e.g.,

microfiltration, ultrafiltration (UF), nanofiltration (NF), and

RO to treat effluent coming out of different units of a

tannery. The possibility of increasing of chloride ions in

permeate, with keeping high chromium(III) retention,

during NF of salt mixture solution characterized by very

low pH has been investigated (Religa et al. 2011b). The

high-chromium retention, amounting to 97–99 %, points

out the possibility of the direct application of NF retentate

in tanning and retanning of skins. In this way, the con-

ducted NF of chromium tannery wastewater will enable the

direct reuse of both retentate–recovered tanning bath (high

concentration of chromium) and permeate–recovered

pickling bath (high concentration of chloride ions (Religa

et al. 2011c).

There are various approaches to address the chromium

issue in tannery wastewater. They are (i) Process control

measures (in-plant control): this includes the treatment of

chrome tanning process waste alone (i.e., from this unit

operation of tanning), treat it for the recovery of chromium

through membrane processes, and/or reuse the treated

effluent water back into process (pickling or pre-tanning

operation) thus an in-plant, closed-loop system. (ii) Out of

plant treatment: collection of the entire composite waste. In

this case, the primary and secondary treatments (and some

preparatory steps) need to be carried out before the

employment of membrane processes, for producing clean,

treated water.

This study conducted to the wastewaters from chrome

tanning process from a leather industry. Both approaches

are applied. While recovery of the chrome is aimed con-

sidering process control measures (in-plant control)

approach, on the other hand with the approach of out of

plant, treatment with the membrane technology alternatives

for the chrome wastewaters and achieving discharge stan-

dards of Turkey is aimed.

In this paper, pressure-driven membrane operations such

as UF, NF, and RO were tested with the wastewater dis-

charged after chromium tanning process. The effects of

membrane type, operating parameters, and separation of

different components were analyzed and discussed. Fur-

thermore the economical evaluation was reviewed.

Materials and methods

Characterization of chrome tanning wastewater

The chrome tanning wastewater was obtained from a lea-

ther-producing process (Bursa area of Turkey). The char-

acteristics of the raw chrome tanning wastewater are given

in Table 1.

ATI UNICAM 929 AA Spectrophotometer was used for

Cr(III) measurements. Electrical conductivity and temper-

ature which exists in feed water have been detected with a

JENWAY Conductivity Meter 4,310, and the pH mea-

surement was analyzed with a PT-10 Sartorious pH meter.

A Flame Photometer was used to detect sodium. Mentioned

analyses were performed by titration method with; sulfate

4,500 D Gravimetric Method, and COD (using closed

reflux method). Suspended solids were performed accord-

ing to Standard Method 2,540 (APHA et al. 1998).

Experimental setup

Membrane experiments were performed at a lab-scale

plant, as shown in Fig. 1. All assays were performed with a

Table 1 Characteristics of the chrome tanning wastewater

Parameter Unit Value

pH – 4.13

Cr(III) mg/L 6,358

Suspended solids (SS) mg/L 980

Chemical oxygen demand (COD) mg/L 5,970

Sulfate (SO4-2) mg/L 30,625

Sodium (Na?) mg/L 27,728

Conductivity ms/cm 79.3

B. Kiril Mert, K. Kestioglu

123

cross-flow module in a flat-membrane test module. Effec-

tive surface area of membrane is 116 cm2. Membrane

system can be operated at a maximum pressure of 40 bar.

Experimental setup was equipped with a high-pressure

pump to achieve the operating pressure and feed circula-

tion. The concentrate stream or retentate was recycled to

the feed tank, and the permeate flow rate was measured by

an electronic balance (Precisa 320 XB-2,200 C) and

recorded by a computer. All the experimental runs were

carried out at a feed volume of 8 L at the beginning of each

run. The temperature of the feed suspension was kept at

±0.5 �C by a cooling apparatus.

Prior to NF and RO experiments, the membranes were

compacted with distilled water for 5 h at the pressures of

21 bar for NF(XN 45) and 30 bar for (ACM2). Cartridge

filters (50, 10, and 5 lm pore size) were used as a prefilter

to remove coarse particulates from wastewaters before

membrane cell.

Membranes

Three distinct types of UF membranes (P150F, P050F, and

P020F), one distinct type of NF membrane (XN 45), and

one distinct type of RO membrane (ACM2) were used in

this study. Properties of these membranes are shown in

Table 2. The operating pressures were 6, 8, and 10 bars for

UF; 20 bar for NF; and 21 bar for RO. The cleaned

membranes were always kept wet in a 0.5 % sodium

bisulfide solution to avoid bacterial growth on the

membranes.

Results and discussion

Studies of 50, 10, and 5 lm pore-diameter cartridge filter

using chrome tanning wastewater.

Analysis of the wastewater following filtration of the

chrome water through a cartridge filter achieved a removal

efficiency of 39 % in the SS parameter. In this way, the

solid load of the chrome waste water which goes through

the treatment alternative was reduced, and the life of the

UF and NF (NP10) membranes used for initial treatment

purposes was thereby extended. In addition, while removal

efficiencies of 22, 19, and 20 % were achieved in the COD,

Cr(III), and SO4-2 parameters, the Na? and conductivity

removal efficiencies were found to be much lower at 2 and

1.5 %, respectively.

Fabiani et al. (1996) suggested that the level of chrome

in waste water is not completely independent, but rather

conjugated to organic substances or solids; or they form

complexes, and therefore, good removal efficiency rates

could be achieved in terms of the level of Cr(III) in the

initial filtering processes. The Cr(III) removal efficiency of

19 % achieved using a cartridge filter can be explained by

the above-mentioned study.

Fig. 1 Laboratory-scale membrane system

Recovery of Cr(III) from tanning process

123

Membrane treatments

UF treatment

Membrane pressure, feed flow rate, temperature, and the

molecular retention weight of the membrane have signifi-

cant effects on permeate flow, which is a very significant

parameter for the evaluation of membrane performance.

Therefore, in the present study, the UF trials were con-

ducted in batch mode using 3 different UF membranes with

MWCO values of 20, 50, and 150 kDa. While the con-

centrate flow was returned by pumping to the feed tank, the

permeate flow was collected separately. The present study

was conducted using three different pressure values, (6, 8,

and 10 bar), while the flow rate was 3 L/min, flow velocity

was 0.3 m/s, temperature was 20 �C, and the pH value was

4. These trials were completed over a period of 4 h. The

flux in the UF membranes became fixed approximately

100 min after the trails started. Temperature was kept

stable, and as stated by Benitez and Acero Leal (2008),

permeate flow increases as a result of the increase in water

viscosity with temperature increase, and the retention

capacity of the membrane decreases. Given this finding, the

optimal temperature for UF membranes was determined as

20 �C.

As can be seen from Fig. 2, the highest flux rate was

obtained in the UF1 (20 kDa) membrane. The flux rate

was found to be 22 L/m2 h at 6 bar, 26 L/m2 h at 8 bar,

and 30.5 L/m2 h at 10 bar. In the UF2 (50 kDa) mem-

brane, the flux rates were found to be 25, 26, and 27 L/

m2 h. In the UF3 (150 kDa) membrane, the flux rates

were found to be 25, 25, and 24 L/m2 h, respectively.

The flux rate obtained with the UF1 membrane at 10 bar

was greater than the UF2 and UF3 membranes, although

the MWCO values are higher. The change in the flux rate

is similar to that reported by Fababuj-Roger et al. (2007),

in which the flux rate of the UF membrane with a

MWCO of 30 kDa was found to be higher than the UF

membrane with a MWCO of 100 kDa. The authors

suggested that this could be explained by the effect of

the molecular size of the solution on membrane con-

tamination. They stated that the 100 kDa UF membrane

retained large particles, and the pores of the membrane

became blocked and contamination increased, thereby

reducing the flux rate.

Table 3 describes the composite permeates obtained at

three different pressure values of 6, 8, and 10 bar using

three different UF membranes with pore diameters of 20,

50, and 150 kDa, respectively. The removal efficiency

rates were obtained by considering the initial concentra-

tions of the contaminants in the chrome tanning wastewater

and their concentrations in the composite permeate.

Generally, the main problem with the recycling of

chrome tanning liquors is the build-up of lipolytic com-

pounds, dissolved salts, and other organic impurities

affecting leather quality (Scholz and Lucas 2003). UF of an

exhaust chromium bath resulted in a strong reduction of

suspended solid components and fat substances.

As stated by Benitez and Acero Leal (2008), the Cr(III),

SS, and COD removal efficiency rates in the UF trials were

greater at higher pressure. The highest permeate quality

was observed in the trials using the UF1 membrane at a

pressure of 10 bar. At 10 bar, the removal efficiency rates

for the COD and SS parameters were 39 and 72 %,

respectively. The concentration values for COD and SS in

the composite permeate were found to be 2,841 and

167 mg/L, respectively.

As can be seen from Table 3, the initial concentration

value of Cr(III) was decreased from 5 150 to 3,376 mg/L.

The Cr(III) removal efficiency rate was found to be 34 %.

The removal efficiency rates for the SS and Cr(III)

parameters, which were found to be 72 and 34 %,

respectively, are similar to those (75 and 37 %) obtained by

Cassano et al. (2001) using a polysulfone UF membrane

with a MWCO of 20 kDa. In the present study, the removal

efficiency of the COD parameter is higher than those

reported by Fababuj-Roger et al. (2007) and Cassano et al.

(1996). Fababuj-Roger et al. (2007) reported a COD

removal efficiency of 16 % using a 30 kDa polysulfone UF

membrane, and Cassano et al. (1996) reported a COD

removal efficiency of 12 % using a 15–25 kDa PVDF UF

membrane.

Furthermore, findings reported in the literature indicate

that higher COD removal efficiency rates are obtained at

lower flow rates. This is because a contamination layer

develops more easily at lower flow rates and natural organic

Table 2 Characteristics of the ultrafiltration, nanofiltration, and reverse osmosis membranes used in experiments

UF membrane UF membrane UF membrane NF membrane RO membrane

Designation P150F P050F P020F XN45 ACM2

Polymer type Polyethersulfone Polyethersulfone Polyethersulfone Polyamide Polyamide

MWCO (Da) 150,000 50,000 20,000 200 –

Area (m2) 0.0116 0.0116 0.0116 0.0116 0.0116

pH range 0–14 0–14 0–14 2–11 2–11


123

substances start to accumulate on this layer. The related

contamination layer acts as an additional filter layer, and the

total resistance for organic substances increases. The

adsorption and sedimentation of organic substances due to

the increased contamination layer causes the COD con-

centration in the permeate to decrease (Benitez et al. 2006;

Ahmad et al. 2005). Therefore, the flow rate of the UF

membranes was determined as 3L/min in the present study.

Table 3 Analysis values and removal efficiencies for permeate water obtained from chrome tanning wastewater using UF membranes [UF1

(20 kDa), UF2 (50 kDa) and UF3 (150 kDa)]

Type of

membrane

Parameter UF feed (Cartidge

Filter Exit) (mg/L)

6 bar 8 bar 10 bar

UF

permeate

(mg/L)

UF removal

efficiency (%)

UF

permeate

(mg/L)

UF removal

efficiency (%)

UF

permeate

(mg/L)

UF removal

efficiency (%)

UF1

(20 kDa)

COD 4,657 3,241 30.4 3,027 35 2,841 39

Cr(III) 5,150 3,729 27.5 3,591 30 3,376 34

SS 598 233 61 197 67 167 72

UF2

(50 kDa)

COD 4,657 3,260 30 3,167 32 3,074 34

Cr(III) 5,150 3,850 25 3,728 27.6 3,646 29

SS 598 359 40 335 44 308 48.5

UF3

(150 kDa)

COD 4,657 3,283 29.5 3,306 29 3,306 29

Cr(III) 5,150 4,031 21.7 4,231 18 3,815 26

SS 598 449 25 431 28 368 38.5

Fig. 2 Temporal flux changes of permeate water passing through a UF1 (20 kDa), b UF2 (50 kDa), and c UF3 (150 kDa) membranes


123

In the UF1 (20 kDa) membrane permeate which would

pass through the NF (XN45) membrane, efficiency was

achieved in the SO4-2, Na? and conductivity parameters

even if just a bit. A removal efficiency of 22 % was

achieved in the SO4-2 parameter, 8 % in the Na? parame-

ter, and 3 % in the conductivity parameter.

Studies conducted with NF (XN45) membrane

The permeate water obtained from the UF1 (20 kDa)

membrane was transferred to the NF (XN45) membrane.

The experiments were conducted in optimal conditions,

which were determined as a result of synthetic studies.

The pressure was 20 bar, temperature was 18 �C, pH was

4, flow rate was 7 L/min, cross-flow rate was 0.7 m/s,

experiment duration was 4 h, and the feed volume was 8

liters, all of which were fixed rates. The flux graphic of

the permeate water obtained from the UF membrane

passing through the NF (XN45) membrane is shown in

Fig. 3.

The initial feed volume for the NF (XN45) membrane

was 8 L, and this decreased to 4.05 L at the end of the

experiment. The VRF value was found to be 1.97. The flux

rate became steady after the 150th minute and was found to

be 47 L/m2 h. The AFM measurements indicated that the

NF (XN45) membrane has a relatively rough structure

(Kaya et al. 2006). This nature of the NF (XN45) mem-

brane causes contaminants to more easily accumulate on

the surface of the membrane and results in high flux losses.

In a study conducted with organic NF of tannery

wastewater, chrome removal efficiency was found to be

60 % in an acidic medium and 30 % in an alkaline medium

(Taleb-Ahmed et al. 2004). Taking the above-mentioned

finding into consideration, the pH value was regulated as 4

in the present trials, as in the synthetic studies. While the

initial concentration of Cr(III) in the feed tank was

3,376 mg/L, this increased to 7,055 mg/L. The Cr(III)

concentration value of the permeate was 164 mg/L. The

removal efficiency increased from around 96–98 % over

time. Similar findings already achieved by Religa et al.

(2013). The Cr(III) amount was thereby doubled when

compared to the initial feed concentration.

Table 4 shows the analysis values and removal effi-

ciencies of the permeate water obtained from passing the

chrome wastewater through the UF1 (20 kDa) membrane,

by the NF (XN45) membrane. Relatively high removal

efficiencies were achieved for the COD (67 %), SS (91 %),

and SO4-2 (92 %) parameters. COD, SS, and SO4

-2 were

thereby reduced to 938, 15, and 1,529 mg/L, respectively.

As in the present study, Galiana-Aleixandre et al. (2005,

2011) achieved over 90 % removal of SO4-2 from pickling

and tannery solutions, and suggested that the low permeate

flux obtained can be directly used in the tanning process.

The contaminant removal efficiency rates are similar to the

findings of previous studies in the literature. Permeate

water of good quality was obtained in the NF (XN45)

membrane except for the conductivity and Na? values. The

conductivity value could be reduced by 13 %, while the

Na? value by 25 %.

A study by Viero et al. (2002) of tannery wastewater

that was passed through a membrane found that the COD

value was 62–86 mg/L as a result of an efficiency higher

than 50 %, and it was concluded that the related permeate

is suitable for reuse for tanning. Following this process, the

study aimed to purify the permeate, obtained from the NF

(XN45) membrane, in the RO (ACM2) membrane to a

level compliant with discharge criteria (Anonymous 2004)

by way of ensuring salt removal.

While the concentration factor was found to be 2 for

Cr(III), the concentration factor for COD was found to be

1.09, which is similar to the findings of Cassano et al.

Fig. 3 Temporal flux change of permeate water obtained from UF1

(20 kDa) membrane passing through NF (XN45) membrane

Table 4 Analysis values and removal efficiencies of filtration of

permeate obtained from chrome tanning wastewater passing through

membrane NF (XN45)

Parameter NF

(XN45)

feed

NF (XN45)

permeate

NF (XN45) removal

efficiency (%)

COD (mg/L) 2,841 938 67

Cr(III) (mg/L) 3,376 164 95

SS 167 15 91

Na? (mg/L) 25,000 18,750 25

SO4-2 (mg/L) 19,110 1,529 92

Conductivity

(ms/cm)

76.5 66.5 13

pH 4.3 4.43 –


123

(1997), indicating that the chrome solution obtained is of

high purity quality. The low amount of the Cr(III) and the

high conductivity of the composite permeate obtained

indicate that it can be reused in tannery and pickling

processes.

Studies conducted with the RO (ACM2) membrane

The permeate water obtained from the NF (XN45) mem-

brane was transferred to the RO (ACM2) membrane. The

experiments were conducted under the conditions obtained

from the synthetic studies. The pressure was 21 bar, tem-

perature was 20 �C, pH was 4, flow rate was 7 L/min,

cross-flow rate was 0.7 m/s, experiment duration was 4 h,

and the feed volume was 8 L, all of which were fixed rates.

Figure 4 shows the flux graphic of the permeate water

obtained from the NF (XN45) membrane passing through

the RO (ACM2) membrane.

The flux rate was found to be 10 L/m2 h. The flux rate

started to decrease due to the residual salts and the resulting

contamination of the RO (ACM2) membrane. Inorganic

solutes might cause contamination during sedimentation

and filtration in the membrane due to hydrolysis and oxi-

dation (Suthanthararajan et al. 2004).

Table 5 gives the temporal change in the permeate and

feed concentration of Cr(III) as a result of the filtration of

the permeate water, which was obtained from the NF

(XN45) membrane, in the RO (ACM2) membrane. The

Cr(III) concentration in the permeate water obtained from

the NF (XN45) membrane was found to be 164 mg. The

Cr(III) was completely removed from the permeate water

that was passed through the RO (ACM2) membrane,

achieving a removal efficiency of 100 %. In a study by

Scholz and Lucas (2003), ultrafiltrated tannery chrome

wastewater was filtrated through a RO membrane with a

flux rate of 21 L/m2 h; this process achieved 100 %

removal of Cr(III) content from the water.

The COD amount in the chrome wastewater that was

passed through the UF1 (20 kDa) and NF (XN45) could

only be reduced to 938 mg/L. This value is not appropriate

in terms of the discharge criterion (Anonymous 2004).

A COD removal efficiency rate of 95 % was achieved

when the wastewater was filtrated in the RO (ACM2)

membrane, and the COD parameter was reduced to 47 mg/

L below the discharge criterion (Anonymous 2004). The

concentrations of Cr(III), conductivity, SO4-2, and SS in the

content of the permeate water obtained from the RO

(ACM2) membrane could be completely removed. Similar

results were obtained by Scholz et al. (2005) who used a

combined treatment of MBR and RO resulting into

90–100 % reduction of COD, BOD tannery effluent.

Keerthi et al. (2013) also verifies the maximum COD

removal of hybrid membrane bioreactor HMBR was found

to be 90.2 %.

The Na? content could only be reduced to 188 mg/L,

despite achieving a removal efficiency of 99 % (Table 5).

Another study about the reuse of tannery wastewater was

conducted by Ranganathan and Kabadgi (2011). In this

study, conventional treatment methods like neutralization,

clari-flocculation, and biological processes were used the

pre-treatment before RO process. About 93–98, 92–99, and

Fig. 4 Temporal flux change of permeate water obtained from NF

(XN45) membrane passing through RO (AMC2) membrane

Table 5 Analysis values and removal efficiencies of filtration obtained from chrome tanning wastewater passing through RO (ACM2)

membrane

Parameter RO(ACM2) feed RO(ACM2)

permeate

RO(ACM2) removal

efficiency (%)

Discharge criterian

(Anonymous 2004)

COD (mg/L) 938 47 95 200

Cr(III) (mg/L) 164 – 100 3

SS (mg/L) 15 – 97 –

Na? (mg/L) 18,750 188 99 –

SO4-2 (mg/L) 1,529 – 100 –

Conductivity (ms/cm) 66.5 – 100 –

pH 4.43 4.7 – 6–9


123

91–96 % removal of TDS, sodium, and chloride, was

achieved for 5 different tanneries. 70–85 % of water could

be recovered and recycled.

In this study; the conductivity of the chrome tanning

effluent (Table 1) is 79 ms/cm and suggests the presence of

high level of salts like NaCl. The high conductivity of the

NF feed (UF permeate) as well as RO feed (NF-permeate)

suggests that neither UF nor NF has removed the salts

which finally appear in RO retentate. Due to the high-

chloride concentration (pickling and tanning effluents), a

RO process is necessary in order to reuse tannery waste-

water (De Gisi et al. 2009).

As can be seen from Table 5, the RO retentate may be

reused in pickling process preceding chrome tanning, and

the content of permeate water obtained from the RO

(ACM2) membrane could be reduced to the discharge

criteria values. The permeate water could, therefore, be

discharged or reused in tanning or painting processes for

tanning yards in need of water of high quality (Suthan-

thararajan et al. 2004).

Cost evaluation

Classical treatment facility treatment cost

A treatment facility of the Leather Organized Industry

Zone consists of physical, chemical, and biological treat-

ment units. The facility was constructed in three steps. The

wastewaters collected from the factories located in various

land plots were carried to the treatment zone through 3

channels (chrome, sulfide, and general wastewaters). In the

Zone of Leather Organized Industry, the chrome waste-

waters were collected in general wastewaters zone after a

chemical treatment. This process resulted in a cost

Table 6 Economic feasibility of the classical treatment alternative of

Leather Industrial Zone

Cr(III) wastewater

Flow (m3/d) 200

Equipment cost, € 129,300

Construction cost, € 175,000

Total process cost, € 43,040

Total process cost, €/m3 0.8

Plant operation was taken as 269 days/year

Table 7 Economic feasibility of the membrane treatment alternative

Membranes UF (20 kDa) NF(XN45) RO(ACM2)

Optimum conditions

Pressure, bar 10 20 21

Recovery, % 90 50 60

Technical conditions

Area, m2 273 160 375

Flow, L/m2 h 30.5 47 10

Membrane quantity 8 8 12

Membrane equipment cost

System cost of spiral wound membrane, € [UF, NF(XN45), RO(ACM2)] 47,000 23,000 13,000

Cost of spiral wound membrane, €/year 22,200 7,200 3,120

Other investments, € 16,685

Tubing cost, € 13,210

Total membrane cost, €/year [UF ? NF(XN45) ? TO(ACM2)] 32,520

Total investment, € 228,415

Process cost

Energy cost, €/y 18,153

Other annual process costs, € 98,411

Total process cost/year 149,084

Total process cost, €/m3 2.77

Annual saving, € 296,936

Saving, €/y 180,372

Saving, €/m3 3.35

Pay-back, months 10

Cartridge filter change period was taken as 2 weeks; membrane change period was taken as 3 times a year; cleaning chemicals were taken as

once a week; and plant operation was taken as 269 days/year


123

increase. So, the cost of chemical and biological treatment

prepared for the chrome zone which had a flow of 200 m3/

d (Table 6).

Membrane treatment cost

The membranes used in the experiments were sized

according to 200 m3/d. The appropriate operating condi-

tions (pressure, temperature, flow rate, and pH) and flux

rates were found for three different membranes: UF, NF

(XN45), and RO (ACM2). The number of membranes and

membrane costs were calculated for these conditions and

are presented in Table 7.

In the cost study for the chrome treatment facility that

includes chemical settling unit for Leather Organized

Industrial Zone, when the cost was compared with the

membrane system, it was found that the investment cost

was higher but the process cost was lower. Besides, chrome

recovery with chemical settling unit was not possible.

Since taking into account the studies already done, the

recovered chrome solution after chemical treatment was at

lower quality considering the presence of the organic

compounds, metals, and other pollutants. Thus, also in

parallel with the literature, it was observed that when

compared to classical treatment methodologies, which are

being used in the treatment of chrome tanning, membrane

technology leather wastewaters was more feasible in terms

of process, cost, and the recovered chrome quality (Scholz

and Lucas 2003).

Conclusions

The present study examined removal efficiencies for per-

meate water obtained from a UF1 (20 kDa) membrane

passed through a NF (XN45) membrane. The removal effi-

ciency rates for SS and Cr(III) were 72 and 34 %, respec-

tively; removal efficiency was 22 % for SO4-2, 8 % for the

Na? parameter; and 3 % for the conductivity parameter.

Removal efficiency rates of 67, 91, and 92 % were achieved

for COD, SS, and SO4-2. While the conductivity value was

reduced by 13 %, the Na? value was reduced by 25 %. The

permeate water of the NF (XN45) membrane was trans-

ferred to the RO (ACM2) membrane. The content in the

obtained permeate water was reduced to appropriate dis-

charge criteria [Cr(III): 2 mg/L, COD: 200 mg/L]. In addi-

tion, the permeate water could be discharged or reused in

tanning or painting processes by tanning yards in need of

water of high quality. When sizing and cost analysis were

conducted for chrome tanning wastewater with a flow rate of

200 m3/d, it was observed that the plant would amortize its

annual operating costs within 10 months. In conclusion, the

investigated ‘‘clean technology’’ application of membranes

brings the possibility of zero-pollutant discharge closer to

reality. The findings clearly demonstrate the benefits and

economic feasibility of membrane applications for chemical

recovery in the leather industry.

Acknowledgments The authors acknowledge the support of Uludag

University Research Projects Department for this project (Project No.

M-2006/31).

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