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Introducing Bio-Scouring: A Cost Effective and Eco-friendly Process for the Generation Next

Abstract:
 
Textiles have undergone wet chemical processing since time immemorial. Human ingenuity and imagination, craftsmanship and resourcefulness are evident in textile products through out the ages; we are to this day awed by beauty and sophistication of textiles sometimes found in archaeological excavations. The paper mainly focuses on bio-scouring process, significant comparison between enzymatic and traditional scouring  processes, contribution of enzyme to reduce cost and the pressure on environment  and discusses some integrated Eco balancing aspects.

Key words: enzyme, bio-scouring, bio-friendly and Eco-balancing      

Introduction:

Now a days, it is becoming important to consumers that the clothes they buy are well made and of high quality material. Additionally, a growing number of consumers are also interested in clothes that are produced in an environmentally friendly way without the extensive use of harsh chemicals.

Enzymatic Scouring or Bio-Scouring can simply be defined as the application of living organisms and their components to remove the natural and added impurities. It is not an industry in itself, but an important technology that will have a large impact on many industrial sectors in the future. Bio Scouring firms will rely mainly on inexpensive substrates for biosynthesis, processes that will function at low temperatures, and will consume little energy and water as well. In Textile Processing the Enzymatic removal of  impurities also reduces the total chemical consumptions and possibilities of accident.

Why Bio-Scouring: (Problems of traditional scouring)

It has become an essential demand for the mill managers to sort out an alternative for the traditional caustic scouring process for some of its unavoidable limitations:

Less fibre strength: In traditional scouring process caustic soda works on swelling method and attacks the secondary cell wall being almost pure cellulose which I have discussed earlier and it causes to damage the fibre and its strength as well.

Excessive weight loss: The recommended weight loss for caustic scouring is 3-8%, but in practice it is around 8-12% which means an excessive loss of fabric weight unnecessarily. The factory has to pay extra money for this unavoidable fabric loss which should not be accepted.

Dye loss: Said earlier that caustic works on swelling method by which all the necessary and unnecessary particles are removed from cotton fibre and most importantly it damages the actual structure of cotton fibre which inspire the dye molecules not to fix according to our requirements and it causes a significant amount of dye loss.

Energy and time concern: In caustic scouring it takes around 105°C temperature and to raise the temperature at this degree it requires a huge amount of energy on which sector we are struggling. Not only that to raise and lower this temperature and also for several rinsing it takes more time which reduces the productivity.

Rinsing and neutralisation: In caustic scouring several rinsing steps are practiced which increase the demand of amount of water volume and as this process is carried out at a high pH range (12-14), it needs to neutralise the scouring bath for the processes ahead.

Effluent concern: A lot of harsh chemicals are used in traditional scouring process which are very much responsible to increase the amount of BOD, COD and TDS in the effluent water and increase the unwanted pressure on environment. Caustic scouring is responsible for the lion parts of the total effluent of a factory. It produces —–

  • 54% to the total BOD
  • 49% to the total COD
  • 10-20% of the total pollution load generated during entire textile processing operation.

Risk in chemical handling: The handling of harsh chemicals increase the possibilities of accident and most importantly the longevity of the workers are badly affected by the handling of this harsh chemicals.

Mechanism involved in Bio-Scouring:

                               cotton_cell

The following two stages mechanisms are involved in bio scouring—

Stage 1:

  • Removal of wax ( a major part being fatty acids, alcohols and esters) is the critical factor for improved wettability.  Pectin functions as a ‘glue’ binding wax to the fibre. Pectin removal  does not by itself result in wax removal or improved wettability but it renders wax extractable or emulsifiable.
  • Presence of  Ca++ slows down the removal pectin and fatty acid, so a sequestrate should, if compatible, be applied with the enzyme – otherwise after the enzyme reaction.

Stage 2:     

  • 2/3 or more of the pectin must be dissolved in order to be able to emulsify enough wax for a good wettability for dyeing.
  • Emulsification is strongly enhanced at temperatures above the wax melting point, i.e. >70°C

Bio-Scouring Process:
Important process parameters:

  • pH and Temperature
  • Wetteners
  • Emulsifiers
  • Pectinase enzyme

                 Application process:
                 
For  Bio- Scouring of cotton fabric Scourzyme L of  Novozymes is used as sample which is an alkaline pectinase and it removes pectin and other impurities from the primary cell wall of the cotton fibres without any degradation of cellulose.

Equipment:  Any type of dyeing m/c used in textile                                                                                      wet processing
Wetting agent                                 :  0.5-1.0 g/l
                  Buffer                                             :  pH (7.5-8.5)
                  Scourzyme L                                  :  0.4-0.6% owf
Emulsifier                                        :  0.5-1.0 g/l
                  Temperature                                   :  55°C
Time                                               :  30 min.

scourzymeFig:  Bio-Scouring with Scourzyme L on knitted fabric

  • Water

Wetting agent
Buffer

  • Scourzyme L
  • Emulsifier                                                    

Advantages of Bio-Scouring over Traditional scouring:
The advantages of bio scouring comparing to traditional scouring can be found in all of the following perspectives—-

  • Quality perspective
  • Economic perspective
  • Environmental perspective

Quality perspective:   It has been described earlier that the main objectives of scouring are—

  • To get the adequate absorbency for further subsequent processes
  • To get the minimum degree of whiteness for medium to dark shades and

maximum degree of whiteness for light and white shades.

             absorbency

Treatment Absorbency (time)
Scourzyme L ( 0.4%) 3 sec.
Scourzyme L ( 0.5%) 2 sec.
Scourzyme L ( 0.6%) 1 sec.
Caustic scouring 1 sec.

Courtesy: Northern Corporation

The AATCC recommended absorbency standard for drop test is in the range of (1-5) sec. So the absorbency of bio scoured fabric is quite satisfactory.

Degree of whiteness:

The whiteness found after bio scouring is quite satisfactory for medium to dark shade but for light and white shade the result is below the satisfaction limit.

whiteness_degreeExcept the above direct qualitative measure of bio scouring, it adds some supplementary quality to the dyed and finished fabric—

  • Level dyeing
  • Soft feeling
  • No strength loss

Economic perspective:

Bio scouring process is very much economical and cost effective comparing to traditional scouring. By considering the following parameters for cost analysis it is found that this process reduces 10-20% of total annual cost which adds a significant amount of profit to the company’s annual turnover.

  • Less chemical cost
  • Energy saving
  • Time saving
  • Less water consumption
  • Less weight loss of fabric
  • Less dye loss
  • Less effluent treatment cost

Less chemical cost:

Cost of Traditional Scouring

Chemicals %, g/l Rate Qty/100 kg fabric Cost/100 kg fabric
Softening agent 0.5 140.46 0.4 56.18
Sequestering agent 0.3 207 0.24 49.68
Non ionic Surfactants 1.0 235 0.80 188.00
Dispersants 0.5 112 0.4 44.80
Caustic Soda 3.0 38 2.4 91.20
Stabilizer 0.3 107 0.24 25.68
Hydrogen Peroxide 2.5 42.88 2.0 85.76
Jet 0.1 235 0.08 18.80
Acetic Acid 1.0 60.5 0.8 48.40
Total Cost 608.50
Cost/kg 6.09

Courtesy: Sinha Knitting Ltd. (Dyeing Division)
                                             

Cost of Bio-Scouring

Chemicals %, g/l Rate Qty/100 kg fabric Cost/100 kg fabric
Softening agent 0.5 140.44 0.4 56.17
Soda Ash 0.4 27.67 0.32 8.85
Non ionic Surfactants 0.3 235 0.24 56.4
Scouring enzyme 0.8 258 0.64 165.12
Jet 0.7 235 0.56 131.6
Dispersants 0.5 112 0.40 44.8
      Total Cost 462.94
      Cost/kg 4.63

Courtesy: Sinha Knitting Ltd. (Dyeing Division)

Energy saving:clip_image002_0003Time saving:
clip_image004_0001Less Water Consumption:clip_image006_0001

Less weight loss of fabric:

Duration Fabric reqd in traditional scouring
(kg)
Fabric reqd in bio scouring
(kg)
Fabric save
(kg)
Cost save
($)
Per shift 4000 3920 80 400
Per day 12000 11760 240 1200
Per month 360000 352800 7200 36000
Annual 4320000 4233600 86400 432000

Courtesy: Northern Corporation

Less Effluent Cost:

Norms of discharged
Water
After traditional scouring After bio scouring Reduction
(%)
Total Cost Reduction
(%)
pH 9.78 7.16 26.78
BOD 215 58 73.12
COD 283 179 36.74 31.55
TDS 1361 1317 3.23
TSS 13 12 13.3
DO 6.21 3.94 36.14

Courtesy: Northern Corporation

Environmental Perspective:
The norms of discharged water after dyeing with traditional scouring and bio scouring can be furnished by the following way. It is an approximate data of Northern Corporation.

Norms of discharged
Water
After traditional scouring After bio scouring Reduction
(%)
pH 9.78 7.16 26.78
BOD 215 58 73.12
COD 283

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