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Management of total dissolved solids in tanning process through improved techniques
Journal of Cleaner Production 13 (2005) 699e703 www.elsevier.com/locate/jclepro
Management of total dissolved solids in tanning process through improved techniques V. Sivakumar, V. John Sundar, T. Rangasamy, C. Muralidharan), G. Swaminathan Central Leather Research Institute, Council of Scientific and Industrial Research, Adyar, Chennai, 600 020, India Received 24 November 2003
Abstract Pickling, one of the pre-tanning operations in leather processing, carried out for conditioning skins prior to tanning contributes to about 35% total dissolved solids (TDS) in the effluents. Treatment of TDS is a technological challenge. Treatment methodologies to combat TDS such as membrane separation have disadvantages of generating large quantities of solid sludge containing concentrated salts and they also suffer from operational difficulties. In-plant process control is necessary for combating TDS issues. In this paper, two approaches viz., recycle/reuse of pickle liquor for the subsequent batches as well as resorting to pickle free alumechrome combination tanning systems have been studied. Pickle liquor from the first batch has been successfully recycled for subsequent batches with appropriate replenishments. The use of potash alum for the pH reduction process has been successfully employed in place of the conventional process. Significant levels of TDS reduction were observed through using both approaches. The strength property and organoleptic property assessments indicate that experimental leathers were comparable with those of leathers processed by the conventional process. It is believed that pickle liquor recycling and pickle free alum chrome combination tanning systems could be gainfully employed to overcome the environmental problems of TDS and chromium problems in the effluent and at the same time effectively obtain economic benefits. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Recycle; Reuse; Leather; Tanning; Pickling; Alum; TDS control
1. Introduction Global leather industry has been facing a major threat with respect to the ecological problems caused by some of its waste streams. The difficulties of the industry in complying with strict environmental regulations in the advanced countries are well known. The various wastewater streams generated during leather processing and their major constituents are given in Table 1. It has also become increasingly evident that the true scientific solutions to the problem can be achieved through in-plant control measures rather than by using end-of-pipe treatment methodologies [1]. Such in-plant control strategies involve:
) Corresponding author. Tel.: C91-44-491-5730; fax: C91-44-4911589. E-mail address: [email protected] (C. Muralidharan). 0959-6526/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jclepro.2004.01.006
Detailed audit of the environmental impact of the various chemical inputs; Optimising the chemical inputs and waste reduction; Development of low or zero waste formulations of known chemical auxiliaries; Development of alternatives to known toxic inputs in the leather-making process; Use of augmentation techniques in leather processing. Collagen is a fibrous protein present in the skins/ hides used in leather making. Pickling is a unit operation carried out after the removal of non-collagenous materials such as epidermis, hair, flesh and opening up the fibre structure. It is primarily carried out for preparing the skin/hide matrix for subsequent tanning process to bring the skin/hide to suitable pH ranges. Generally, pH of 2.8e3.0 is suitable for chrome tanning and 4.5e5.0 for vegetable tanning. Conventionally,
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Table 1 Waste streams generated from unit operations in leather processing and their major constituents Unit operation
Major constituents
Soak liquor
Chlorides, soluble proteins, wetting agents. Sulphide, lime, hair and dissolved proteins. Dissolved proteins and ammonium salts Unspent acid and neutral salt Unspent chrome and neutral salts Neutral salts Unspent chemicals
Lime liquor Delime liquor Pickle liquor Chrome tan liquor Neutralisation liquor Retanning, dyeing, fatliquoring liquor
formic and sulphuric acids are used in the brine solution with salt concentration of 8e10(Be [2]. Brine solution is necessary; otherwise protein swells in acid solution leading to fibre distortion. Alternatively, naphthalene sulphonic acid, which has no swelling effect, can be employed to avoid the use of salt [3]. Alum pickle and recycle of pickle liquor can also be employed [4]. Indian standards related to disposal of treated tannery effluent is given by Bureau of Indian Standards [5]. Among the problems in complying with the standards, total dissolved solids (TDS) present in the tannery effluent are yet to be resolved. While the treated tannery effluents have TDS value of about 7000e10 000 ppm, the Indian standard for the TDS in the treated effluent is prescribed to be 2100 ppm. About 35% of TDS generated from tannery effluents sent to the primary treatment plant are from the pickling process. Even though treatment methodologies such as membrane separation (ultra-filtration) [6,7] or reverse-osmosis [8] and electro-dialysis [9] have been employed, they have the inherent problem of generation of solid wastes in the form of salts which must be separated from the effluent. Therefore, one of the more sustainable solutions to overcome the TDS problem in the leather processing is to adopt process innovations. In this paper, closed loop reuse/recycle of pickle liquor generated from the first batch for use in subsequent batches leading to near zero discharge of pickle liquor as well as adoption of alum pickling technique prior to chrome tanning, have been studied.
1.1. Recycle/reuse of pickle liquor About 800 l of water and 80 kg of salt are used in the pickling process for every tonne of hides/skins. About 50e60% of the salt and acid used are usually sent to the waste stream. Effective utilisation of salt and acid present in the used pickle liquor by recycle and reuse methods have been studied in the present work.
1.2. Alum pickle and chrome tanning ‘Tawing’ one of the oldest methods of tanning utilises Potash alum K2SO4Al2(SO4)324H2O as the tanning agent. Potash alum dissolved in water produces basic aluminium sulphate and sulphuric acid as shown in the following equation, Al2 ðSO4 Þ3 C2 H2 O/2AlðOHÞSO4 CH2 SO4 Acid produced can be utilised for lowering the pH to 3.0, when 3.5% potash alum (% based on the pelt weight) is used. Neutral salt potassium sulphate present in the potash alum is utilised to control acid swelling of skin protein. 2. Experimental methods 2.1. Recycle of pickle liquor Wet-salted goatskins (10 skins) were taken, trimmed, cut open and individual weights of each skin were documented. Each skin was cut across the backbone in to left and right portions for comparison of the experimental and control process. The process was performed similarily to that of the controls up to the deliming. The skins were soaked with 300% water, 0.5% non-ionic wetting agent (% based on raw skin weight) for 3 h in a pit. The soaked skins were pasted on the flesh side with a paste made of 3% sodium sulphide, 10% lime and 20% water and piled flesh to flesh overnight. The next day, the skins were unhaired using the blunt knife and relimed for 2 days with 300% water and 10% lime. Then, the skins were defleshed in a fleshing machine and scudded. The weight of the fleshed pelt having 80% moisture content was taken as the basis for further operations. Then, the skins were delimed using 100% water, 1% ammonium chloride for 1 h and bating was carried out with 1% alkaline bate. Completion of deliming was checked using phenolphthalein indicator for absence of pink colour at the cross section of the skins. Then, the delimed pelts were washed in plain water and then pickled. For the first pickling process, 80% water, 8% common salt, 0.5% formic acid (1:10 w/v solution) were used and drummed for 30 min, then 1% sulphuric acid (1:10 w/v solution) was added in 3 feeds of 10 min interval and then drummed for 1 h. The spent pickle liquor was collected. Acid and salt content of the used pickle liquor was determined by chemical analysis. On ensuring pH-2.8 at the cross section of the pelt, the skins were chrome tanned by the conventional method [10] using 8% basic chromium sulphate (BCS) and piled overnight. Next day, the wet-blue leathers were sammed in a sammying machine and shaved to 1 mm thickness. The shaved weight of the leathers was noted. Then, the
V. Sivakumar et al. / Journal of Cleaner Production 13 (2005) 699e703
leathers were rechromed with 5% BCS (% based on shaved weight), neutralised to pH-5.2. Then, the leathers were retanned with 8% syntan, fat-liquored with 8% fat-liquor, 2% acid dye and then fixed using 1% formic acid. Then, the leathers were piled overnight. The next day, the leathers were hooked to dry, set, staked, trimmed, buffed and then assessed.
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Table 3 Uptake of salt in the pickle liquor recycling experiments Experiment
% uptake
I batch I recycle (II batch) IX recycle (X batch)
50 G 2 57 G 2 59 G 2
to be 4.0. Then, further processing up to dyeing was performed as done for the control leather.
2.2. Pickle liquor recycle I Pickle liquor from batch-I was analysed for its acid and salt content and given in Tables 2 and 3, respectively. Recycle I of the pickle liquor was performed by using 80% pickle liquor from the batch-I, 5.3% sodium chloride (% based on fleshed pelt weight) and 0.75% sulphuric acid. Pickling was performed by the same procedure followed for the batch-I. The amount of salt and acid added for this recycle 1 is for replenishing the pickle liquor from batch I to make the concentration of salt 8% and acid 1% based on the pelt weight of the skin. 2.3. Recycle II to IX Recycle experiments II to IX were performed by using 80% pickle liquor from the previous cycle along with 4.5% sodium chloride and 0.37% sulphuric acid. The percentage of chemicals used is based on the fleshed pelt weight and average value for recycle experiments. Pickling was performed with the same procedure followed for the batch I. 2.4. Alum pickling and chrome tanning Wet-salted goatskins were taken, trimmed, cut open and the weights were noted. The processing was carried out similar to that for control up to deliming. Then, the skins were washed in plain water and then alum pickling and chrome tanning was performed using 80% water, 3.5% potash alum (% based on fleshed pelt weight) added in two feeds of 30 min interval and then drumming for further 60 min. The pH at the cross section was adjusted to 3.0. Then, 5% BCS was added in two feeds of 30 min interval and then drumming for further 60 min. The bath was then basified using 1% sodium formate and 1% sodium bi carbonate over a period of 2 h. The pH of the cross section was checked Table 2 Uptake of acid in the pickle liquor recycling experiments Experiment
% uptake
I batch I recycle (II batch) IX recycle (X batch)
63 G 2 65 G 2 62 G 2
2.5. Spent liquor analysis The spent liquors were analysed for bio-chemical oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS), acid content, salt content, chrome content, aluminium content as per the American Water Works Association (AWWA) method [11]. 2.6. Strength property analysis Strength characteristics of the dyed crust leathers such as tensile strength [12] and tongue tear strength [13] were tested using an Instron tensile tester and grain crack and grain burst [13] were tested using lastometer. Leather samples for the physical testing were taken parallel to backbone from the dyed leather samples following the IUP/1 procedure for sampling and testing [14]. 2.7. Organoleptic functional property analysis Dyed crust leathers were subjected to organoleptic assessment for softness, fullness, grain smoothness, grain tightness (break), dyeing characteristics and general appearance by hand and visual examination. The leathers were rated based on a scale of 0e10 grade points for each functional property by experienced professionals in the leather field. The higher grade points indicate better property for the subsequent end usage of leather.
3. Results and discussions 3.1. Recycle of pickle liquor Recycling of pickle liquor facilitates reduction of water input, salt usage and TDS in waste streams. The salient features of this are, It was found that the uptake of acid and salt in pickling operation was nearly 63% and 55% of the input, respectively. The spent pickle liquor was reused for pickling of subsequent batches, after replenishing with necessary
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Table 4 Organoleptic properties of dyed crust leathers for the recycle of pickle liquor experiments Property
I batch
II batch
X batch
E
C
E
C
E
C
Softness Fullness Grain smoothness Grain tightness Dyeing characteristics General appearance
6 G 0:5 7 G 0:4 6 G 0:5 6 G 0:5 7 G 0:2 6 G 0:5
7 G 0:5 6 G 0:3 6 G 0:5 7 G 0:2 6 G 0:5 6 G 0:5
6 G 0:4 5 G 0:5 7 G 0:5 6 G 0:5 6 G 0:5 7 G 0:5
7 G 0:5 6 G 0:5 7 G 0:5 7 G 0:3 7 G 0:5 6 G 0:5
7 G 0:5 5 G 0:3 6 G 0:5 6 G 0:2 6 G 0:5 6 G 0:5
7 G 0:3 5 G 0:5 6 G 0:5 7 G 0:5 6 G 0:4 7 G 0:5
E, experiment; C, control.
quantities of salt and acid, to maintain the appropriate concentrations. The BOD, COD and TDS of the liquors were analysed for the spent liquors. It was found that the TDS of the wastewater could be reduced by more than 45% through recycling of pickle liquors. The visual assessment of the leathers did not show any appreciable change in surface or in functional properties as shown in Table 4 for the organoleptic properties for the leathers Strength characteristics of the leathers are also comparable as given in Table 5.
Table 5 Strength property analyses of dyed crust leather from recycle of pickle liquor experiments Property
I batch E
II batch C
E
X batch C
E
C
Tensile 145 G 2 144 G 2 150 G 1 140 G 2 210 G 2 175 G 2 strength (kg/cm2) Tongue tear 17 G 1 17 G 2 20 G 2 17 G 1 18 G 1 30 G 2 strength (kg/cm) Grain crack 40 G 2 40 G 2 20 G 1 40 G 1 30 G 2 40 G 2 strength (kg) Grain crack 14 G 1 15 G 2 8 G 1 13 G 1 12 G 1 14 G 2 distension (mm) E, experiment; C, control.
3.2. Alum pickling and chrome tanning In case of pickle free alumechrome combination tanning, the following important findings were documented: Complete elimination of pickling operation; Significant savings in material as less chromium is used (5% instead of conventional 8%) and exhaustion characteristics of Cr were as high as 90e92%; Significant reductions in COD and TDS were observed as shown in Table 6; Use of chlorides in processing was eliminated completely. Reduction in CODd63% Reduction in TDSd49% The crust leathers had improved grain characteristics and dyeing properties as shown in Table 7; No adverse changes in strength properties were observed as shown in Table 8.
Table 7 Organoleptic properties of dyed crust leathers for the alum pickling and chrome tanning experiments Property
Experiment
Control
Softness Fullness Grain smoothness Grain tightness Dyeing characteristics General appearance
7 G 0:5 6 G 0:5 6 G 0:3 6 G 0:5 7 G 0:5 6 G 0:4
7 G 0:5 5 G 0:4 7 G 0:5 7 G 0:5 6 G 0:3 6 G 0:5
On 10 point scale 0, poor; 10, excellent. Table 6 Spent liquor analysis for alum pickling and chrome tanning process Parameter
Experiment
Control
BOD COD TDS Cl % exhaustion of Cr % exhaustion of Al
1200 1250 25640 233 91 66
2667 3345 49830 37408 71 e
All figures, mean values of two determinations, are in ppm except % exhaustion
Table 8 Strength property analysis of dyed crust leather for alum pickling and chrome tanning process Property 2
Tensile strength (kg/cm ) Tongue tear strength (kg/cm) Grain crack strength (kg) Distension (mm)
Experiment
Control
155 G 0:5 26 G 0:4
150 G 0:5 20 G 0:3
25 G 0:5
28 G 0:5
9 G 0:3
10 G 0:4
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V. Sivakumar et al. / Journal of Cleaner Production 13 (2005) 699e703 Table 9 Cost benefit analysis for recycle of pickle liquor experiments (cost calculated for processing 1 tonne of fleshed pelt) % chemicals and cost
Recycle experiments I batch
IIdX batch
IdX batch
% sulphuric acid required
1%!1 ¼ 1% Total ¼ 4:33% US$ 5.24 8%!1 ¼ 8% Total ¼ 48:5% US$ 21.34 US$ 26.58 US$ 20.72
0:37%!9 ¼ 3:33%
1%!10 ¼ 10%
4:5%!9 ¼ 40:5%
US$ 12.10 8%!10 ¼ 80%
Cost (A) @ US$ 0.121/kg % salt required Cost (B) @ US$ 0.044/kg Total cost (ACB) Savings
Table 10 Cost benefit analysis for alum pickling and chrome tanning process (cost calculated for processing 1 tonne of fleshed pelt) % chemicals and cost
Alum pickling and chrome tanning
Control
% alum required Cost (A) @ US$ 0.143/kg % BCS required Cost (B) @ US$ 0.771/kg Formic acid Cost (C) @ US$ 1.013/kg Sulphuric acid Cost (D) @ US$ 0.121/kg Total cost (ACBCCCD) Savings
3.5% US$ 5.01 5% US$ 38.55 e e e e US$ 43.56 US$ 24.395
e e 8% US$ 61.68 0.5% US$ 5.065 1% US$ 1.21 US$ 67.955
Control
US$ 35.20 US$ 47.30
to overcome the TDS problem in the effluent effectively with added cost benefits.
Acknowledgements
3.3. Cost benefit analysis and environmental benefits The cost benefit analysis for the recycle of pickle liquor as well as alum pickling and chrome tanning processes are shown in Tables 9 and 10, respectively. In the case of recycle of pickle liquor experiments, on average 0.37% sulphuric acid and 0.45% salt were added in the pickle liquor from previous batch for replenishment. The analysis indicates that savings of about US$ 20 for recycle of pickle liquor experiments and US$ 24 for alum pickling and chrome tanning method for processing 1 tonne of materials (based on fleshed pelt weight). In addition to the benefits in terms of cost, these novel approaches also enjoy significant reduction in TDS and concomitant reduction in the pollution problems to meet the standards specified for tannery effluents.
4. Conclusions Pickle liquor recycling and pickle free alum chrome combination tanning systems can be gainfully employed
The authors thank Dr T. Ramasami, Director, CLRI for encouragement regarding this work. One of the author V.S. thank C.S.I.R, India for research fellowship.
References [1] Sivakumar V. PhD thesis, Anna University, Chennai, India; 2001. [2] BASF, West Germany, Pocket book for the leather technologist; 1972. [3] Sacchev S, Niagolov K. Rev Tech Indus du Cuir 1982;74:130. [4] Sivakumar V. M.Tech thesis, Anna University, Chennai, India; 1996. [5] Bureau of Indian standards for discharge of industrial effluents BIS, IS-2490, Part-3, India; 1985. [6] Viero F, Mazzarollo ACR, Wada K, Tessaro IC. Desalination 2002;149(1e3):145e9. [7] Alves AMB, de Pinho MN. Desalination 2000;130(2):147e54. [8] Cassano R, Molinari R, Romano M, Drioli E, Membrane J. J Membrane Sci 2001;181(1):111e26. [9] Raghava Rao J, Prasad BGS, Narasimhan V, Ramasami T, Shah PR, Khan AA. J. Membrane Sci 1989;46(2e3):215e24. [10] Muralidharan C, Sundar VJ, Sundara Rao VSJ. J Am Leather Chem Assoc 2001;96(2):61e6. [11] American Water Works Association (AWWA). Standard methods for the examination of water and wastewater. 20th ed. USA; 1998. Published jointly by American Water Works Association, American Public Health Association, and Water Environment Federation. [12] SLTC (Society of leather technologists and chemists). IULTCS, Official methods. UK; 1996. [13] SATRA. Test procedures. Northamptonshire, UK; 1992. [14] IUP (International union of leather chemists societies physical testing commission. IUP Recommended physical test methodsd IUP/1. J Soc Leather Technol Chem Soc 1958;42:382e93.
Management of total dissolved solids in tanning process through improved techniques V. Sivakumar, V. John Sundar, T. Rangasamy, C. Muralidharan), G. Swaminathan Central Leather Research Institute, Council of Scientific and Industrial Research, Adyar, Chennai, 600 020, India Received 24 November 2003
Abstract Pickling, one of the pre-tanning operations in leather processing, carried out for conditioning skins prior to tanning contributes to about 35% total dissolved solids (TDS) in the effluents. Treatment of TDS is a technological challenge. Treatment methodologies to combat TDS such as membrane separation have disadvantages of generating large quantities of solid sludge containing concentrated salts and they also suffer from operational difficulties. In-plant process control is necessary for combating TDS issues. In this paper, two approaches viz., recycle/reuse of pickle liquor for the subsequent batches as well as resorting to pickle free alumechrome combination tanning systems have been studied. Pickle liquor from the first batch has been successfully recycled for subsequent batches with appropriate replenishments. The use of potash alum for the pH reduction process has been successfully employed in place of the conventional process. Significant levels of TDS reduction were observed through using both approaches. The strength property and organoleptic property assessments indicate that experimental leathers were comparable with those of leathers processed by the conventional process. It is believed that pickle liquor recycling and pickle free alum chrome combination tanning systems could be gainfully employed to overcome the environmental problems of TDS and chromium problems in the effluent and at the same time effectively obtain economic benefits. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Recycle; Reuse; Leather; Tanning; Pickling; Alum; TDS control
1. Introduction Global leather industry has been facing a major threat with respect to the ecological problems caused by some of its waste streams. The difficulties of the industry in complying with strict environmental regulations in the advanced countries are well known. The various wastewater streams generated during leather processing and their major constituents are given in Table 1. It has also become increasingly evident that the true scientific solutions to the problem can be achieved through in-plant control measures rather than by using end-of-pipe treatment methodologies [1]. Such in-plant control strategies involve:
) Corresponding author. Tel.: C91-44-491-5730; fax: C91-44-4911589. E-mail address: [email protected] (C. Muralidharan). 0959-6526/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jclepro.2004.01.006
Detailed audit of the environmental impact of the various chemical inputs; Optimising the chemical inputs and waste reduction; Development of low or zero waste formulations of known chemical auxiliaries; Development of alternatives to known toxic inputs in the leather-making process; Use of augmentation techniques in leather processing. Collagen is a fibrous protein present in the skins/ hides used in leather making. Pickling is a unit operation carried out after the removal of non-collagenous materials such as epidermis, hair, flesh and opening up the fibre structure. It is primarily carried out for preparing the skin/hide matrix for subsequent tanning process to bring the skin/hide to suitable pH ranges. Generally, pH of 2.8e3.0 is suitable for chrome tanning and 4.5e5.0 for vegetable tanning. Conventionally,
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V. Sivakumar et al. / Journal of Cleaner Production 13 (2005) 699e703
Table 1 Waste streams generated from unit operations in leather processing and their major constituents Unit operation
Major constituents
Soak liquor
Chlorides, soluble proteins, wetting agents. Sulphide, lime, hair and dissolved proteins. Dissolved proteins and ammonium salts Unspent acid and neutral salt Unspent chrome and neutral salts Neutral salts Unspent chemicals
Lime liquor Delime liquor Pickle liquor Chrome tan liquor Neutralisation liquor Retanning, dyeing, fatliquoring liquor
formic and sulphuric acids are used in the brine solution with salt concentration of 8e10(Be [2]. Brine solution is necessary; otherwise protein swells in acid solution leading to fibre distortion. Alternatively, naphthalene sulphonic acid, which has no swelling effect, can be employed to avoid the use of salt [3]. Alum pickle and recycle of pickle liquor can also be employed [4]. Indian standards related to disposal of treated tannery effluent is given by Bureau of Indian Standards [5]. Among the problems in complying with the standards, total dissolved solids (TDS) present in the tannery effluent are yet to be resolved. While the treated tannery effluents have TDS value of about 7000e10 000 ppm, the Indian standard for the TDS in the treated effluent is prescribed to be 2100 ppm. About 35% of TDS generated from tannery effluents sent to the primary treatment plant are from the pickling process. Even though treatment methodologies such as membrane separation (ultra-filtration) [6,7] or reverse-osmosis [8] and electro-dialysis [9] have been employed, they have the inherent problem of generation of solid wastes in the form of salts which must be separated from the effluent. Therefore, one of the more sustainable solutions to overcome the TDS problem in the leather processing is to adopt process innovations. In this paper, closed loop reuse/recycle of pickle liquor generated from the first batch for use in subsequent batches leading to near zero discharge of pickle liquor as well as adoption of alum pickling technique prior to chrome tanning, have been studied.
1.1. Recycle/reuse of pickle liquor About 800 l of water and 80 kg of salt are used in the pickling process for every tonne of hides/skins. About 50e60% of the salt and acid used are usually sent to the waste stream. Effective utilisation of salt and acid present in the used pickle liquor by recycle and reuse methods have been studied in the present work.
1.2. Alum pickle and chrome tanning ‘Tawing’ one of the oldest methods of tanning utilises Potash alum K2SO4Al2(SO4)324H2O as the tanning agent. Potash alum dissolved in water produces basic aluminium sulphate and sulphuric acid as shown in the following equation, Al2 ðSO4 Þ3 C2 H2 O/2AlðOHÞSO4 CH2 SO4 Acid produced can be utilised for lowering the pH to 3.0, when 3.5% potash alum (% based on the pelt weight) is used. Neutral salt potassium sulphate present in the potash alum is utilised to control acid swelling of skin protein. 2. Experimental methods 2.1. Recycle of pickle liquor Wet-salted goatskins (10 skins) were taken, trimmed, cut open and individual weights of each skin were documented. Each skin was cut across the backbone in to left and right portions for comparison of the experimental and control process. The process was performed similarily to that of the controls up to the deliming. The skins were soaked with 300% water, 0.5% non-ionic wetting agent (% based on raw skin weight) for 3 h in a pit. The soaked skins were pasted on the flesh side with a paste made of 3% sodium sulphide, 10% lime and 20% water and piled flesh to flesh overnight. The next day, the skins were unhaired using the blunt knife and relimed for 2 days with 300% water and 10% lime. Then, the skins were defleshed in a fleshing machine and scudded. The weight of the fleshed pelt having 80% moisture content was taken as the basis for further operations. Then, the skins were delimed using 100% water, 1% ammonium chloride for 1 h and bating was carried out with 1% alkaline bate. Completion of deliming was checked using phenolphthalein indicator for absence of pink colour at the cross section of the skins. Then, the delimed pelts were washed in plain water and then pickled. For the first pickling process, 80% water, 8% common salt, 0.5% formic acid (1:10 w/v solution) were used and drummed for 30 min, then 1% sulphuric acid (1:10 w/v solution) was added in 3 feeds of 10 min interval and then drummed for 1 h. The spent pickle liquor was collected. Acid and salt content of the used pickle liquor was determined by chemical analysis. On ensuring pH-2.8 at the cross section of the pelt, the skins were chrome tanned by the conventional method [10] using 8% basic chromium sulphate (BCS) and piled overnight. Next day, the wet-blue leathers were sammed in a sammying machine and shaved to 1 mm thickness. The shaved weight of the leathers was noted. Then, the
V. Sivakumar et al. / Journal of Cleaner Production 13 (2005) 699e703
leathers were rechromed with 5% BCS (% based on shaved weight), neutralised to pH-5.2. Then, the leathers were retanned with 8% syntan, fat-liquored with 8% fat-liquor, 2% acid dye and then fixed using 1% formic acid. Then, the leathers were piled overnight. The next day, the leathers were hooked to dry, set, staked, trimmed, buffed and then assessed.
701
Table 3 Uptake of salt in the pickle liquor recycling experiments Experiment
% uptake
I batch I recycle (II batch) IX recycle (X batch)
50 G 2 57 G 2 59 G 2
to be 4.0. Then, further processing up to dyeing was performed as done for the control leather.
2.2. Pickle liquor recycle I Pickle liquor from batch-I was analysed for its acid and salt content and given in Tables 2 and 3, respectively. Recycle I of the pickle liquor was performed by using 80% pickle liquor from the batch-I, 5.3% sodium chloride (% based on fleshed pelt weight) and 0.75% sulphuric acid. Pickling was performed by the same procedure followed for the batch-I. The amount of salt and acid added for this recycle 1 is for replenishing the pickle liquor from batch I to make the concentration of salt 8% and acid 1% based on the pelt weight of the skin. 2.3. Recycle II to IX Recycle experiments II to IX were performed by using 80% pickle liquor from the previous cycle along with 4.5% sodium chloride and 0.37% sulphuric acid. The percentage of chemicals used is based on the fleshed pelt weight and average value for recycle experiments. Pickling was performed with the same procedure followed for the batch I. 2.4. Alum pickling and chrome tanning Wet-salted goatskins were taken, trimmed, cut open and the weights were noted. The processing was carried out similar to that for control up to deliming. Then, the skins were washed in plain water and then alum pickling and chrome tanning was performed using 80% water, 3.5% potash alum (% based on fleshed pelt weight) added in two feeds of 30 min interval and then drumming for further 60 min. The pH at the cross section was adjusted to 3.0. Then, 5% BCS was added in two feeds of 30 min interval and then drumming for further 60 min. The bath was then basified using 1% sodium formate and 1% sodium bi carbonate over a period of 2 h. The pH of the cross section was checked Table 2 Uptake of acid in the pickle liquor recycling experiments Experiment
% uptake
I batch I recycle (II batch) IX recycle (X batch)
63 G 2 65 G 2 62 G 2
2.5. Spent liquor analysis The spent liquors were analysed for bio-chemical oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS), acid content, salt content, chrome content, aluminium content as per the American Water Works Association (AWWA) method [11]. 2.6. Strength property analysis Strength characteristics of the dyed crust leathers such as tensile strength [12] and tongue tear strength [13] were tested using an Instron tensile tester and grain crack and grain burst [13] were tested using lastometer. Leather samples for the physical testing were taken parallel to backbone from the dyed leather samples following the IUP/1 procedure for sampling and testing [14]. 2.7. Organoleptic functional property analysis Dyed crust leathers were subjected to organoleptic assessment for softness, fullness, grain smoothness, grain tightness (break), dyeing characteristics and general appearance by hand and visual examination. The leathers were rated based on a scale of 0e10 grade points for each functional property by experienced professionals in the leather field. The higher grade points indicate better property for the subsequent end usage of leather.
3. Results and discussions 3.1. Recycle of pickle liquor Recycling of pickle liquor facilitates reduction of water input, salt usage and TDS in waste streams. The salient features of this are, It was found that the uptake of acid and salt in pickling operation was nearly 63% and 55% of the input, respectively. The spent pickle liquor was reused for pickling of subsequent batches, after replenishing with necessary
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Table 4 Organoleptic properties of dyed crust leathers for the recycle of pickle liquor experiments Property
I batch
II batch
X batch
E
C
E
C
E
C
Softness Fullness Grain smoothness Grain tightness Dyeing characteristics General appearance
6 G 0:5 7 G 0:4 6 G 0:5 6 G 0:5 7 G 0:2 6 G 0:5
7 G 0:5 6 G 0:3 6 G 0:5 7 G 0:2 6 G 0:5 6 G 0:5
6 G 0:4 5 G 0:5 7 G 0:5 6 G 0:5 6 G 0:5 7 G 0:5
7 G 0:5 6 G 0:5 7 G 0:5 7 G 0:3 7 G 0:5 6 G 0:5
7 G 0:5 5 G 0:3 6 G 0:5 6 G 0:2 6 G 0:5 6 G 0:5
7 G 0:3 5 G 0:5 6 G 0:5 7 G 0:5 6 G 0:4 7 G 0:5
E, experiment; C, control.
quantities of salt and acid, to maintain the appropriate concentrations. The BOD, COD and TDS of the liquors were analysed for the spent liquors. It was found that the TDS of the wastewater could be reduced by more than 45% through recycling of pickle liquors. The visual assessment of the leathers did not show any appreciable change in surface or in functional properties as shown in Table 4 for the organoleptic properties for the leathers Strength characteristics of the leathers are also comparable as given in Table 5.
Table 5 Strength property analyses of dyed crust leather from recycle of pickle liquor experiments Property
I batch E
II batch C
E
X batch C
E
C
Tensile 145 G 2 144 G 2 150 G 1 140 G 2 210 G 2 175 G 2 strength (kg/cm2) Tongue tear 17 G 1 17 G 2 20 G 2 17 G 1 18 G 1 30 G 2 strength (kg/cm) Grain crack 40 G 2 40 G 2 20 G 1 40 G 1 30 G 2 40 G 2 strength (kg) Grain crack 14 G 1 15 G 2 8 G 1 13 G 1 12 G 1 14 G 2 distension (mm) E, experiment; C, control.
3.2. Alum pickling and chrome tanning In case of pickle free alumechrome combination tanning, the following important findings were documented: Complete elimination of pickling operation; Significant savings in material as less chromium is used (5% instead of conventional 8%) and exhaustion characteristics of Cr were as high as 90e92%; Significant reductions in COD and TDS were observed as shown in Table 6; Use of chlorides in processing was eliminated completely. Reduction in CODd63% Reduction in TDSd49% The crust leathers had improved grain characteristics and dyeing properties as shown in Table 7; No adverse changes in strength properties were observed as shown in Table 8.
Table 7 Organoleptic properties of dyed crust leathers for the alum pickling and chrome tanning experiments Property
Experiment
Control
Softness Fullness Grain smoothness Grain tightness Dyeing characteristics General appearance
7 G 0:5 6 G 0:5 6 G 0:3 6 G 0:5 7 G 0:5 6 G 0:4
7 G 0:5 5 G 0:4 7 G 0:5 7 G 0:5 6 G 0:3 6 G 0:5
On 10 point scale 0, poor; 10, excellent. Table 6 Spent liquor analysis for alum pickling and chrome tanning process Parameter
Experiment
Control
BOD COD TDS Cl % exhaustion of Cr % exhaustion of Al
1200 1250 25640 233 91 66
2667 3345 49830 37408 71 e
All figures, mean values of two determinations, are in ppm except % exhaustion
Table 8 Strength property analysis of dyed crust leather for alum pickling and chrome tanning process Property 2
Tensile strength (kg/cm ) Tongue tear strength (kg/cm) Grain crack strength (kg) Distension (mm)
Experiment
Control
155 G 0:5 26 G 0:4
150 G 0:5 20 G 0:3
25 G 0:5
28 G 0:5
9 G 0:3
10 G 0:4
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V. Sivakumar et al. / Journal of Cleaner Production 13 (2005) 699e703 Table 9 Cost benefit analysis for recycle of pickle liquor experiments (cost calculated for processing 1 tonne of fleshed pelt) % chemicals and cost
Recycle experiments I batch
IIdX batch
IdX batch
% sulphuric acid required
1%!1 ¼ 1% Total ¼ 4:33% US$ 5.24 8%!1 ¼ 8% Total ¼ 48:5% US$ 21.34 US$ 26.58 US$ 20.72
0:37%!9 ¼ 3:33%
1%!10 ¼ 10%
4:5%!9 ¼ 40:5%
US$ 12.10 8%!10 ¼ 80%
Cost (A) @ US$ 0.121/kg % salt required Cost (B) @ US$ 0.044/kg Total cost (ACB) Savings
Table 10 Cost benefit analysis for alum pickling and chrome tanning process (cost calculated for processing 1 tonne of fleshed pelt) % chemicals and cost
Alum pickling and chrome tanning
Control
% alum required Cost (A) @ US$ 0.143/kg % BCS required Cost (B) @ US$ 0.771/kg Formic acid Cost (C) @ US$ 1.013/kg Sulphuric acid Cost (D) @ US$ 0.121/kg Total cost (ACBCCCD) Savings
3.5% US$ 5.01 5% US$ 38.55 e e e e US$ 43.56 US$ 24.395
e e 8% US$ 61.68 0.5% US$ 5.065 1% US$ 1.21 US$ 67.955
Control
US$ 35.20 US$ 47.30
to overcome the TDS problem in the effluent effectively with added cost benefits.
Acknowledgements
3.3. Cost benefit analysis and environmental benefits The cost benefit analysis for the recycle of pickle liquor as well as alum pickling and chrome tanning processes are shown in Tables 9 and 10, respectively. In the case of recycle of pickle liquor experiments, on average 0.37% sulphuric acid and 0.45% salt were added in the pickle liquor from previous batch for replenishment. The analysis indicates that savings of about US$ 20 for recycle of pickle liquor experiments and US$ 24 for alum pickling and chrome tanning method for processing 1 tonne of materials (based on fleshed pelt weight). In addition to the benefits in terms of cost, these novel approaches also enjoy significant reduction in TDS and concomitant reduction in the pollution problems to meet the standards specified for tannery effluents.
4. Conclusions Pickle liquor recycling and pickle free alum chrome combination tanning systems can be gainfully employed
The authors thank Dr T. Ramasami, Director, CLRI for encouragement regarding this work. One of the author V.S. thank C.S.I.R, India for research fellowship.
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