Enzyme finishing (Denmark)

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1. Case study or Built example

Built example

2. Industry Sector

Textile finishing industry.

3. Industrial application

The use of the enzyme Terminox Ultra to neutralize the fabric after bleaching and before dyeing.

4. Process description
  • Process flowsheet:

No information is available.

  • Processes:

Natural fabrics such as cotton are normally bleached with hydrogen peroxide before dyeing. Bleaching agents are highly reactive chemicals and even very small amounts of hydrogen peroxide can interfere with the dyeing process. That is why thorough 'bleach cleanup' is necessary. Bleach Cleanup is a term chosen by Novo Nordisk to describe this process of removing residual hydrogen peroxide after bleaching and prior to dyeing [1].

The traditional method is to remove the bleaching agent by rinsing the fabric with large quantities of water several times. Alternatively a reducing agent like thiosulfate can be used to neutralize the bleach but the dose has to be controlled precisely. Also a higher temperature is required in order to react efficiently with hydrogen peroxide. After the reduction the remaining reducing agent has to be rinsed out. In either case, large amounts of water are required for rinsing: up till 40 litres per kg of fabric.

5. Energy flows and temperature ranges
  • Main heat supply system and fuel:

The natural gas is used for the steam generation at the dyehouse.

  • Energy consumption (Sankey):

No information is available.

  • Temperature ranges and other parameters:

No information is available.

6. New technology’s description

Enzymes provide a more convenient alternative because they are easier and quicker to use. A small dose of Catalase is capable of decomposing hydrogen peroxide to water and oxygen. Compared with the traditional clean-up method, the enzymatic process results in a reduced water consumption and a reduced energy consumption. The enzyme can be applied directly after the bleaching stage. The Terminox Bleach Cleanup process recommended for batch processing in e.g. Yarn dyeing equipment, Jet dyers and winches is as follows [2]:

1. Drain the bleaching liquor
2. Fill with fresh cold water
3. Adjust pH as for dyeing
4. Add 0.5-1.0 g/l Terminox
5. Check hydrogen peroxide after 10 - 15 min.
6. Start dyeing in same liquor

The rinsing step is not required when using the enzyme because the bleaching agent is decomposed and the residues of the enzyme have no effect on textile fibres or dyestuffs. In cases where the fabric is very dirty it is recommended to include a rinsing step between bleaching and dyeing.

Terminox Ultra (commercial name of the Novo enzyme) is a tabilized liquid catalase, found in nature and produced by submerged fermentation of a non-pathogenic microorganism. The enzyme specifically breaks down hydrogen peroxide into non-active oxygen and water under mild temperature conditions.

2 H2O2 --> O2 + 2 H2O

The activity of the enzyme is 10 KCIU/g. One KCIU activity unit ( Kilo Catalase International Unit) is the amount of enzyme that breaks down one millimole of hydrogen peroxide per minute under standard conditions ( 25 C, pH 7.0, 10 millimole H2O2)[2]. Under industrial conditions, Terminox Ultra takes 10 to 15 minutes to breakdown the hydrogen peroxide completely and then the dye can be added. This also means that time can be saved.

Saving energy (thereby preventing the associated emissions ) and saving water are the main environmental benefits compared to conventional bleach clean up, especially in developing countries where water is usually a scarce resource. In industrialized countries, water is often more readily available but water charges are usually high for both fresh water and for treating waste water.

The advantages of the enzyme are:

  • No adverse effect on dyestuffs
  • No need for heating
  • No need for rinsing prior to dyeing
  • No risk of harmful overdosing
  • No formation of by products in waste water

7. Energy savings
  • Pinch analysis results:

No information is available.

  • Energy savings:

The trial is done with 470 kg knitted 100% cotton fabric with a machine capacity of 500 kg. The results of this test are passed on to the 1500 tons dyed in a year to calculate the yearly savings.

TABLE 1: material/energy balance

Material balance-Enzyme finishing (Denmark).jpg

TABLE 2: Savings when using the enzyme instead of a reducing agent.

Savings when using the enzyme instead of a reducing agent-Enzyme finishing (Denmark).jpg

Terminox Ultra consumption  : 5-10 tons per year

The quantity of gas is converted to the quantity of energy in GJ. The basic heating value of natural gas is assumed to be 39.1 MJ/m3.

As no heating is required when the enzymatic treatment is used, considerable amounts of gas can be saved giving reductions in carbon dioxide emissions of an estimated 160 tons per year. This is the main advantage from the environmental point of view. However, from the economical point of view, the savings in water charges are most significant. Instead of 19 litres per kg of fabric, only 10 litres were required for the Bleach Clean up stage [1].

The dye house tested the color shade and fastness, and found no difference between the processes. The bursting strength of samples were tested internally, and again no difference could be found between the two samples [3].

Neither Terminox, nor the reducing agent applied as alternative, had any significant impact on the waste water quality. Impurities from the cotton fabric (pectines and spinning oil) were the main contributors to BOD5 and COD.

8. Economic evaluation
  • Economic parameters:

Investment Costs

There are no investment costs. The same machine is used and no further equipment is necessary.

Operational and Maintenance Costs

There are no additional operational and maintenance costs. The difference in price of terminox and thiosulfate depends on the supplier ( of thiosulfate) as well as the geographical market. The cost savings in a particular country will depend on local water charges and the costs for energy. To calculate the cost savings for a hypothetical case the following assumptions for energy and water costs have been made. Natural gas: 1 DKK/m3 and water 15 DKK/m3. Using these assumptions the cost savings, as a result of the use of Terminox, are 27500 DKK per year, based on the reductions in water and energy consumptions indicated in table 1.

Payback Time

While the investment cost are zero the payback time is also zero. The new process starts to give benefits as soon as it is used.

Reviewer's Comments:

This case study was submitted to UNEP IE by the Institute for Applied Environmental Economics (TME) of the Netherlands on the part of the UNEP IE working group on Biotechnology. The case study was edited for the ICPIC diskette in August 1995. It has not undergone a formal technical review.


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