Indian Journal of Fibre & Textile Research Vol. 25, March 2000, pp. 75-8\

Effluent treatment in textile processing: Part I-Bleaching of cotton fabric

H T Deo· & S K Chinta

Division of Technology of Fibres and Textile Processing, Department of Chemical Technology, University of Mumbai , Mumbai 400 019, India

Received 1 Jun e 1998; revised received and accepted 24 December 1998

Bleaching of cotton fabric has been carried out by various formulations (Formulations \ - VI) with a view to have easily treatable effluent of reduced volume. It is observed that Formulation VI is the most efficient processing sequence wherein the bleaching time is reduced from 18 h in a conventional method to just 5 h, thereby enhancing the production three fold s. The number of washings is also reduced from 8 to only 3, giving considerable saving in water consumption apart from reducing the effluent load by over 59%. Steam, electricity, and overall savings in Formulation VI are 67%, 72% and 33.8% respectively when compared to those in the con ventional bleaching process. The new process is totall y eco- fri endl y as it avoids the use of any of the chlorine-based bleaching agents or chemicals.

Keywords: Bleaching, Effluent treatment, Cotton fabric , Wet processing, Eco-friendly processing

1 Introduction In the field of textiles, wet processors have been

facing a lot of criticism over the last decade for increasing environmental pollution . The sector's association with toxic chemicals has stained its image. Processing of textiles without chemicals and dyes is not possible as these are required for enhancing the aesthetic appeal and imparting special fini shes l

•2

.

Fibre preparation to garment packing operations generate a substantial amount of waste'. In making all these textile products, more than 8,000 chemicals are used4

. Textile wet processing operations usually generate larger volumes of effluents, which are complex in nature and variable both in regard to quality and characteri stics. Specially designed tre~t~ent plants should be abl~ to cope up wit~ these vanatlOns' . Cotton processing needs different bleaching agents and different classes of dye, as compared to synthetics and their blends6

.

To decide about the type of treatment , all the basic facts, such as the nature of the material processed (cotton, synthetic, wool, silk, etc), operations carried out , quantity and nature of chemicals, machinery employed, characteristics and volume of waste, mode of effluent disposal (into water courses or sewers), possibility of using spent baths, recycling of water and wastes and future expansions of the industry, should be collected and exami ned critica ll y. While

aTo whom all the correspondence may be addressed. Present address: 18 Safalya, 19-20 Nath Pai Nagar, Ghatkopar (East), Mumbai 400 077.

treating the effluent, the waste water is purified by precipitation and biological methods5

.7

.

Various techniques employed to reduce pollution at source are: ( 1) qual ity control of dyes and chemicals, (2) inventory management, (3) chemical/dye substitutions, (4) conservation/optimization of dyes and chemicals, (5) water conservation, (6) process modification, (7) equipment modification, and (8) reuse and recovery.

Recent technological advances are mainl y aimed at cost reduction, quality upgradation, energy and water conservation, and to decrease the quantity and upgrade the quality of effluent8

.

Neutralization of alkaline textile effluents, generated in scouring and bleaching process, by an anaerobic biological procedure, has already been studied. The effluents were biologicall y neutralized in a continuous way up to the pH 8.0 - 8.5 (ref. 9). The effect of sodium hypochl orite used In textile bleaching on water pollution was studied by Moskalink and Kataovic lO

. The advanced processing of scouring and dyeing effluents by ozone treatment, with hydrogen peroxide and radiation (Gamma radiation) and various combinations have already been reviewed II . Attempts have also been made to reduce the effluent pollution from the pretreatment

' processes of cotton by modifying production processes and substituting chemicals and auxiliaries that are more environment-friendli 2

.

The present work aims at developing effect ive bleaching processes for cotton fabrics with a view to

76 INDIAN J. FIBRE TEXT. RES. , MARCH 2000

reduce effluent load by adopting various process modifications through chemical substitution, shortening the process sequence and reducing water, steam, and electricity consumption.

2 Materials and Methods Cotton long cloth (warp count, lOs; weft count,

20s; endslin., 36; and pickslin., 48) was used . Hydrochloric acid, caustic soda, Sequacol-20

(sequestering agent), Ultracar C (anionic wetting agent), anthraquinone, sodium hypochlorite, hydrogen peroxide, sodium carbonate, peroxide stabilizer A WNI, Cidascour L TJ -100 (low temperature scouring agent), sodium hydrosulphite, glucose (reducing agent) ,and cowdung were used for the study.

2.1 Bleaching The cotton fabric samples were bleached separately

by conventional process and modified processes using Formulations I-VI developed in our laboratories. The processing sequence was changed in all the formulations and the effluent generated was collected. Bleaching was carried out first in the laboratory and then scaled up to the industrial level. Typical practical data for the calculation of steam, water and electrical energy consumption are given in Appendix 1.

2.1.1 Conventional Bleaching The long cloth fabric was desized with 0.5% HCI

and 1 gpl wetting agent at room temperature for 120 min followed by hot and cold water wash. Scouring was then carried out using 3.0% (owt) sodium hydroxide, 0.1 % (owt) sequestering agent, 0.1 % (owf) anionic detergent and 0.75% (owf) anthraquinone in a kier at 130°C for 8 h. The scoured fabric was subjected to hot and cold water wash and chemicking was can-ied out using sodium hypochlorite (3.0 gpl available chlorine) at room temperature (30°C) for 2 h. The fabric was then washed and bleached with 0.75% (owf) hydrogen peroxide (50%), 0.2% (owf) sodium carbonate and 0.5% (owf) peroxide stabilizer A WNI at 85°C for 4 h. The bleached fabric was washed with hot and cold water, soured, washed again and dried.

2.1.2 Bleaching Formulation I After desizing and washing the fabric, as described

above, it was subjected to combined scouring and bleaching action by treating it with 0.75% (owf) low temperature scouring agent, sodium hypochlorite (4.0 gpl available chlorine), 0.1 % (OWf) anionic detergent and 0.2% (owf) sodium carbonate (for maintaining the pH at 10.0- 10.5) at room temperature for 2 h. The

treated fabric was then given hot and cold water wash before souring with 0.1 % (owf) hydrochloric acid. Finally, the fabric was washed twice with water and dried.

2.1.3 Bleaching Formulation II The fabric was desized with sodium hypochlorite

(1 .5 gpl available chlorine), 0.1 % (owf) anionic detergent at room temperature for 2 h, followed by hot and cold water wash . The fabric was then subjected to combined scouring and bleaching as described in Formulation I.

2.1.4 Bleaching Formulation III

The fabric was desized with HC) as described in conventional method of bleaching and then subjected to combined scouring and bleaching by treating it with 2.0% caustic soda, 1.5% sodium metasilicate, 0.6% magnesium sulphate, 0.5% low temperature scouring agent, 2.0% hydrogen peroxiode (50%) and 0.5% potassium persulphate at room temperature for 2 h. The fabric was then washed twice with hot and cold water, soured, washed again and dried.

2.1.5 Bleaching Formulation IV The acid desized and washed sample was given a

combined scouring and bleaching treatment using 2.5% (owf) caustic soda, 0.5% (owf) sodium metasilicate, 0.1 % (owf) anionic detergent, 1.0% (owf) hydrogen peroxide (50%) and O.l % (owf) sequestering agent at boil for 6 h. The fabric was then washed twice with hot and cold water, soured, washed again and dried.

2.1.6 Bleaching Formulation V The grey fabric was first treated with 0.1 % anionic

wetting agent at boil for 15 min and then 2% caustic soda was added to the same bath, and the treatment continued for 15 min. Further, 0.5% low temperature scouring agent was added twice at an interval of 15 min and the treatment was continued for 2 h. Sodium hydrosulphite (I %) was then added in the same bath and treatment continued for 15 min more. 1 % hydrogen peroxide (50%) and 0.5% peroxide stabilizer A WNI were then added to the same bath and bleaching continued for 1 h more. The fabric was then washed twice with hot and cold water before souring. The c0.!l1plete treatment was can-ied out at boil.

2.1.7 Bleaching Formulation VI The grey fabric was treated with 0.1 % anionic

wetting agent at boil for 15 min and then 3% caustic

DEO & CHINT A: EFFLUENT TREATMENT IN TEXTILE PROCESSING: PART I 77

soda was added in the bath and the treatment continued for 15 min more. The reducing agent glucose (1 % owf) was added to it and the treatment continued for 2 h. Sodium hydrosulphite (1.0%) was added to this bath and after 15 min, 1.5% hydrogen peroxide (50%) was added and the treatment continued for I h. The total treatment was carried out at boil only. The fabric was finally washed with hot and cold water before souring.

2.2 Treatment of Effiuent

2.2.1 Equalization The effluent from all the unit processes, like

desizing, scouring and bleaching, was collected, filtered through filter cloth and then stored for a period of 6 h. The temperature was allowed to cool down to 30°C before it was taken for further. treatment.

2.2.2 Neutralization of Alkaline Waste The alkaline effluent was neutralized by using

sulphuric acid, maintaining pH at 7.8-8.0.

2.2.3 Aeration The neutralized effluent was given aeration

treatment for I h with the help of air compressor.

2.2.4.Coagulation and Flocculation The aerated effluent was treated with 100 mg/litre

alum [Ah(S04h] and 0.2 mg/litre polyelectrolyte. The mixing was carried out very fast within a minute. The treated effluent was then stirred gently to mix the contents properly for a period of 15 min to agglomerate the impurities in the form of rapidly settling floc . The floc was allowed to settle down for 60 min, subsequently leaving clear supernatant liquor.

2.2.5 Aeration The clear supernatant liquor was given the aeration

treatment for 4 h. A few traces of cowdung and diammonium phosphate were added before the aeration starts. After the completion of aeration, the liquor was allowed to settle down for 45 min and the clear supernatant liquor was separated.

2.2.6 Sand and Activated Carbon Column The column was prepared by using granules of

activated carbon sandwiched between the fine sand layers. The column was washed thrice. The clear supernatant liquor was passed through the activated carbon column slowly and collected at the bottom in the receiving flask.

2.3 Tests

2.3.1 Measurement of Tensile Strength The treated fabric samples were first conditioned

and then measured for tensile strength as per the standard method 13.

2.3.2 Determination of Absorbency The absorbency of fabric was determined following

the standard AATCC method l4. The sample was

conditioned in a desiccator at 25°C with 65% RH for 4 h and then clamped tight on an embroidery ring. A drop of water was put on the sample and the time required for its disappearance was noted.

2.3.3 Determination of Whiteness Value The whiteness values were determined on a high

volume tester (930 Colorimeter) which directly gives the values of percentage reflection, i.e. whiteness (Hunter Scale).

2.3.4 Determination of Total Suspended Solids Total suspended solids (TSS) were determined by

the filtration methods.

2.3.5 Total Dissolved Solids A known volume of the effluent sample was

filtered through a glass micro fibre · filter paper and filtrate was then evaporated in a porcelain dish. Increase in weight gave the total di ssolved solid (TDS) contentss.

2.3.6 Biological Oxygen Demand Biological oxygen demand (BOD) was determined

by dilution of effluent followed by the titrimetric methodS.

2.3.7 Chemical Oxygen Demand The organic matter of the sample was oxidized to

water, carbon dioxide and ammonia by refluxing with a known excess quantity of potassium dichromate in 50% sulphuric acid solution . Silver sulphate was added as a catalyst for promoting oxidation and mercuric sulphate was added for eliminating interference due to chlorides. The excess dichromate was then titrated with a standard solution of ferrous ammonium sulphates.

2.3.8 Determination of Carboxyl Value The carboxyl content was determined by the

iodometric method as reported earlier l5.

3 Results and Discussion Table I shows that the conventional method of

bleaching requires 18 h, whereas bleaching with

78 INDIAN J. FIBRE TEXT. RES., MARCH 2000

Formulations I-VI requires substantially less time e.g. 9.5 hand 5 h with Formulation IV and Formulation VI respectively . This is due to the reduced number of washings from 8 in conventional bleaching to only 3 in these formulations. This not only saves time but also increases the production almost by more than three folds. As the number of washings decreases, the quantity of water required for bleaching per kg of fabric also decreases from 110 litres to 45 litres. This results in saving of time and water by 72.66% and 59.09% respectively in the case of Formulation VI. When the conventional method of bleaching is compared with the six formulations , Formulation VI seems to be the most efficient one as far as time and water savings are concerned.

Table 2 shows that in conventional method, the total bleaching cost including those of chemical, steam, electricity and water comes around Rs. 5079.0. Formulations I and II offer more advantages as far as steam cost is concerned. These treatments were carried out at room temperature and here no steam cost is involved, thereby giving net savings of 59.31 %, which is the highest amongst all other formulations. In the case of Formulations V and VI, there is net saving in thermal, electrical and water costs as the number of steps in bleaching and washing is reduced which results in saving of time as well. Thus, it appears that Formulations V and VI, which

give cost reduction of 31.68% and 33.84% respectively, are efficient as far as cost saving factor is concerned. Moreover, no hypochlorite is involved in bleaching with these two formulations.

Table 3 shows that the loss in tensile strength of the bleached fabric is higher in conventional method but comparatively less in case of other formulations . Absorbency of all the treated samples including those with conventional method is found to be less than 3' s, which is quite satisfactory. The carboxyl content, which indicates the chemical degradation of cellulose, is found to be 0 .75 for conventionally bleached sample, whereas it is less for Formulations I-VI. This shows that the degradation or deterioration of the samples bleached with Formulations I-VI is not enough to be observed . Although Formulations I-IV offer slight decrease in whiteness, Formulations V and VI, on the other hand, give better results in this regard .

Table 4 shows the results of analysis of effluent generated by conventional bleaching as well as by different formulations . The pH value for all the formulations is around 10, which is highly alkaline due to the use of strong alkali used in the bleaching process . The total suspended solids are found to be less in all the formulation s as compared to that in conventional method. Formulation III gives the lowest va lue of TSS (3985 mg/litre). As against this, the

Table I-Effect of different bleaching sequences on process parameters

Process No. of Time Saving Water No. of Saving Cost of bleaching steps required in time required washings in water ( I kg fabric)

h % litres/kg of fabri c % Rs

Conventional 14 18.0 110 08 2.54

Formulation I 09 5.5 69.44 67 05 39.09 1.69

Formulation II 09 5.5 69.44 67 05 39.09 1.69

Formul ation III 09 5.5 69.44 67 05 39.09 2.48

Formulation IV 09 9.5 47.22 67 05 39.09 1.48

Formulation V 06 5.5 71.33 45 03 59.09 2.59

Formulation VI 06 5.0 72.66 45 03 59.09 2.87

Table 2-Effect of different bleaching sequences on processing 1000 kg fabric

Process Cost of Cost of Saving Cost of Saving in Cost of Saving Cost of Savi ng chemicals stearn in stearn electricity electricity water in water bleaching in cost

Rs Rs % Rs % Rs % Rs %

Conventional 2540 1800 54.0 605 5059.0

Formulation I 1690 100 16.5 69 .44 360 40.50 2066.5 59.3 1

Formulation II 1690 100 16.5 69.44 360 40.50 2066.5 59.31

Formulation III 2480 100 16.5 69.44 360 40.50 2856.5 43 .76

Formulation IV 1480 628.5 66.57 28.5 47.22 360 40.50 2497.0 50.84

Formul ati on V 2590 615 67.29 15.0 72.22 250 58.68 3470.0 31.68

Formulation VI 2480 6 15 67. 29 15.0 72.22 250 58.68 3360.0 33.84

DEO & CHINTA: EFFLUENT TREATMENT IN TEXTILE PROCESSING: PART I 79

Table 3-Effect of different formulations on quality of bleached fabric

Process Tensi le strength Absorbency Carboxyl Whiteness kgf s group (Hunter)

Warp Weft content %

Grey 38.3 35.1

Conventional 32.5 27.5 <3 0.75 85.006

Formulation I 34.2 28.2 <3 0.74 83.959

Formulation II 33.6 28.1 <3 0.79 84.612

Formulation III 34. 1 28.4 <3 0.71 83.214

Formulation IV . 32.9 28.0 <3 0.66 84.612

Formulation V 33.9 28.8 <3 0.73 86.819

Formulation VI 33.9 28.6 <3 0.72 85.880

Table 4 - Analysis of waste water generated by different formulations

Process pH Total Biological Chemical Total Total suspended

solids mg/litre

Conventional 10.3 7338

Formulation I 10.2 4201

Formulation II 10.2 4097

Formulation III 10.8 3985

Formulation IV 10.7 4135

Formulation V 9.4 4731

Formulation VI 9.5 4230

comparatively higher value of TSS in case of Formulation V (4731 mg/litre) may be due to more number of processes under drastic conditions of temperature used in this formulations as against Formulation III.

The Biological Oxygen Demand (BOD) is an important criterion for depletion · of oxygen . Formulations I-VI show lower values of BOD as compared to conventional method . It can be observed that Formulations IV and VI give the lowest BOD value of 251 mg/litre each. The higher BOD for the conventionally bleached sample may be due to the use of more number of chemjcals and their higher dosages.

The Chemical Oxygen Demand (COD) for conventionally bleached effluent is found to be higher (1523 mg/litre), whereas it is the lowest for Formulations V and VI (515 mg/litre). The reasons for low values of COD for Formulations I-VI may be the use of less number of chemicals and their small dosages. The total residual ch lorine is found to be more in the case of Formulation II (3200 mg/ litre), whereas it is less in the case of conventional bleaching (2700 mg/litre) and Formulatuion I (2800

oxygen oxygen residual dissolved demand demand chlorine solids mg/litre mg/litre mg/litre mg/litres

427 1523 2700 8975

312 835 2800 7325

323 843 3200 7201

329 923 7375

251 735 8121

265 515 6500

251 515 6271

mg/ litre) . This may be because of the hypochlorite desizing and bleaching in case of Formulation II. As there is no hypochlorite involved in Formulations ill­VI, no residual chlorine is found for these formulations. The Total Dissolved Solids are higher in the case of conventional bleaching than those in the case of Formulations I-VI. Formulations V and VI show lower values of TDS and thus indicate that these formulations are more efficient as far as effluent quality is concerned. The above findings indicate that the quality of the effluent, in general, generated in various formulations is much better than that generated in conventional method,particularly in case of Formulations V and VI. Due to the reduced load in the effluents generated in Formulations V and VI, the effluent could be treated in much easier way in shorter duration of time.

Table 5 shows the results of analysis of treated effluent. The pH values are corrected in the range of 8.1- 8.3 and are found to be within the norms of Pollution Control Board l 6

. The values of TSS, TDS, BOD and COD have also been reduced and are found to be within the norms of Pollution Control Board. The residual chlorine in effluents generated in

80 INDIAN 1. FIBRE TEXT. RES., MARCH 2000

Table 5 - Analysis of treated effluents

Process pH Total suspended

solids mg/litre

Conventional 8.3 79

Formulation I 8.2 68

Formulation II 8.2 68

Formulation III 8.2 74

Formulation IV 8.2 74

Formulation V 8.2 75

Formulation V[ 8. [ 75

Pollution 5.5-9.0 100

Control Board

(PCB) norms

Total Biological dissolved oxygen

solids demand mg/litre mg/litre

2350 28

1675 28

1600 28

1721 27

1839 27

1521 31

1525 30

2100 30

Chemical oxygen demand mg/litre

175

184

167

179

189

165

160

250

Residual chlorine mg/litre

0.3

0.3

0.4

1.0

Table 6-Effect of different formulations on effluent generation and its treatment cost for 1000 kg fabric

Process Effluent Reduction Treatment Saving in generated in effluent cost treatment cost

litre

Conventional 1,10,000

Formulation [ 67 ,000

Fonnulation II 67 ,000

Formulation III 67,000

Formulation IV 67,000

Formulation V 45 ,000

Formulation V[ 45 ,000

conventional bleaching and Formulation I is around 0.3 mg / litre each, while it is higher at 0.4 mg/ litre for Formulation II. This may be due to the higher dosage of hypochlorite in Formulation II. However, it is also within the norms of Pollution Control Board.

Table 6 shows the effluent load and cost of its treatment. The effluent generated in conventional method is 1,10,000 litres per 1,000 kg of fabric. Whereas it is 45,000 litres each in Formulations V and VI. This gives the savings of 59.09% in effluent load in these two Formulations . The lower volumes of effluent generated in Formulations I-VI may be due to the less number of steps and washings involved in these formulation s. The cost of effluent treatment is found to be Rs .330 in case of conventional method and Rs.135 in case of Formulations V and VI each, thereby giving net savings of 59.09% in effluent treatment cost for Formulations V and VI each. Even the Formulations I-IV give net savings of 39.09% each. This shows that if the effluent load is reduced, the treatment cost will also be reduced by many folds . Considering the awareness regard ing the protection of environment, the wet processors must treat the

% Rs %

330

39.09 201 39.09

39.09 201 39.09

39.09 201 39.09

39.09 201 39.09

59.09 135 59.09

59.09 135 59.09

effluent before it gets discharged . The daily recurring expenses for treating the effluent, however, is a problem. Hence, Formulations V and VI may offer advantages in reducing effluent treatment costs.

4 Conclusions Formulation VI is the most efficient bleaching

process and may offer the following advantages without affecting the quality of bleached fabric : • Treatment time is reduced from 18 h to 5 h only.

This may increase the production rate by more than three folds.

• As the number of washings are reduced from 8 to 3, there is a net saving of water of 65 litres/kg of fabric, i.e. from 1 10 litres/kg to 45 litres/kg of fabric.

• A net saving of 67 .29% in thermal energy in the form of steam and 72.22% in electrical energy is observed. The saving in water consumption is almost 58.68% and the total saving is around 33 .84% as against conventional method of bleaching.

DEO & CHINTA: EFFLUENT TREATMENT IN TEXTILE PROCESSING: PART I 81

• The analysis of treated effluent indicates that the parameters are according to the norms of Pollution Control Board.

• The reduction in water consumption not only decreases the cost of water required but also reduces the cost of effluent treatment by 59.09%.

• As Formulation VI does not require any solvent or hypochlorite, the process is totally eco­friendly.

• Though the cost of bleaching is slightly higher than that of conventional method of bleaching, the savings and other benefits are very high, giving overall savings in the bleaching of long cloth with the new formulations suggested in this work.

References 1 Subramanium S & Phalgumani G R, Book of Papers, 52n

'/ All India Textile Conference on Modern Technology Management in Textiles [Textile Associ ation (India)], 1996, 197.

2 Rao C S, Environmental pollution control engineering (Wiley Eastern Limited, New Delhi), 1991 .

3 Topalian J, Text Trend, 38 (4) (1995) 29. 4 Lokhande H T & Naik S R, Book of Papers, 52rn.i All India

Textile Conference on Modern Technology Management in Textiles [Textile Association (India)] , 1996, 182.

5 Manivaskam N, Treatment of textile processing effluents, (Sakthi Publications, Coimbatore), 1995.

6 Thakore K A & Mehta K S, Book of Papers, 18th A TIRA Technical Conference, (ATIRA, Ahmedabad), 1977.

7 Desai C, Colourage, 40 (8) (1993) 39. 8 Andreas W & Dietrich F, Melliand Textilber, 74 (9) (1993)

E325.

9 Crespi M & Yilaseca M, Boletin Intexter, (1996) 37; World Text Abstr, 29 (1997) 1748, 148.

10 Moskalink K & Kataovic D, Tekstil, 46 (3) (1997) 139; World Text Abstr, 29 (1997) 5854, 506.

II Perkowski J, Kos L & Ledakowicz S, Przeglad Wlokienniczy, 51 (5) (1997) 27; World Text Abstr, 29 (1997) 6515.

12 Cheng K M, Book of Papers, International Conference and Exhibition, (American Association of Textile Chemists and Colorists, Atlanta), 1997, 28; World Text Abstr, 30 (1998) 492,54.

13 lSI Handbook (Indian Standards Institution), 1983 , 44. 14 AATCC technical manual, (American Association of Textile

Chemists and Colorists, Atlanta), 1975, 171 . 15 Majumdar P, Sanyal S, Dasgupta B, Show S C & Guha Roy

T K. Indian J Fibre Text Res, 19 (1994) 286. 16 Indian standard specifications, IS:2490 (Bureau of Indian

Standards,New Delhi) 1981 .

Appendix -Typical practical data for calculation of steam, water and electrical energy

Steam consumption:

-Scouring

-Peroxide boil

-Scouring-cum-bleaching

Rating of kier circulation pump

Motor of washing machine

Water required for machine

Cost

-Steam

-Electricity

-Water

: 1.8 kg/kg of fabric

: 1.0 kg/kg of fabric

: 1.0 kg/kg of fabric

: 5 HP (3 .75 kW)

: 5 HP (3.75 kW)

: 10 Iitres/kg of fabri c

: Rs 0.60/kg

: Rs 3.00 /kWh

: Rs 55.00/1 0,000 litre