The prevention of discharge of hazardous chemicals used in textile processing operations is always looked at as a ‘COST’ that is to be incurred for mandatory compliance requirements –enforced either by a Brand or by local regulatory authorities. All chemical management and effluent treatment exercises are aimed at eliminating or limiting the exposure of such chemicals in the final outputs (viz product, effluent and air emissions) or within the workplace.

However, zero discharge of hazardous chemicals can also be looked at as a ‘PROFIT’ centre by incorporating innovative techniques and ‘green’ chemistry alternatives that help to reduce costs through savings in input resources such as chemicals, water & energy and result in increased productivity as well as reduced impact on wastewater treatment costs.

Let me enumerate some of these techniques:

1.  Reduce chemicals that ‘go down the drain’:

Many chemicals that are used to process fabrics and garments are NOT actually included in the final product, but are simply ‘washed down the drain’. These are called as “Non- productive outputs”. The total cost of these undesired outputs can be anywhere between 15- 30% of the total production costs , including disposal costs .If these are simply eliminated or reduced in the various processes, it directly results in cost-savings. Let me illustrate this with 2 examples:

Example 1: Scour- bleach process of Cotton Knits

The table above illustrates the chemicals used in a conventional scour-bleach recipe versus a recipe using ENZYMES for scour- bleach of a 140 gsm Cotton Knit fabric. The use of enzymes reduces the usage of Caustic Soda (that is used as an alkali in the scour-bleach process) from 1.75 grams per litre to 0.5 grams per litre. Thus, for a knits dyehouse dyeing about 20 tons per day, with an average liquor ratio of 1:6, the amount of caustic soda consumption can be reduced from 210 kgs per day to 60 kgs per day! At an average cost of half a dollar per kg of caustic, a saving of $75 per day can be effected. The lesser use of caustic soda also drastically reduces the COD load on the Effluent Treatment Plant, thereby indirectly reducing the chemical costs for effluent treatment!

Example 2:  Dyeing of pale shades with direct dyes in place of reactive dyes

Reactive Dyes are the most popular dye class used for dyeing of cotton. However, almost 25 -40% of the dye is not fixed on the cotton fibre and gets this unfixed dye needs to be washed out, resulting in use of large amounts of water and washing agents. Additionally, salt used for exhaustion of the reactive dyes during dyeing process also goes down the drain. Thus, unfixed reactive dyes , salt and washing agents used in reactive dyeing process are all non-productive outputs!

How do we reduce these undesired outputs?  By using Specialty Direct Dyes dye pale shades – say upto 1.5% depth – in place of reactive dyes by exhaust dyeing process.

The above table shows a comparison of the direct dyeing and reactive dyeing processes for light shades. The dye quantity required to dye the same depth of shade with direct dye is half or one-third of a reactive dye. The salt quantity requirement is also 1/5^th, which also helps to reduce the Total Dissolved Solids (TDS) load on the Effluent Treatment Plant. Direct Dyes need only a simple Cold Water wash – there is no need to use any washing agents! This type of dyeing not only helps to save chemical and water costs, but also improves productivity by reducing the total dyeing cycle time and eliminates the use of washing agents that may contain APEO contamination!

2. Improving the ‘Right First Time’ (RFT) Dyeing Rate:

Right First Time Dyeing means achieving the target shade in the first attempt itself – without any additions of chemicals or re-processing the dyed fabric. In simple terms, RFT means “Fill it, shut it, forget it”, meaning the fabric load should be taken out of the dyeing machine in the first shot itself. This is a challenging task, since there are so many process variables to be controlled in the dyeing and finishing cycle.

RFT improvement can have a huge impact on your profitability. The table above shows a study by P.S.Collishaw, DAS Phillip and M J Bradbury published in a JSDC issue on the impact on productivity and profits due to shade additions in dyeing. If Blind dyeing, i.e dyeing without any additions is taken as a base of 100, then a small addition results in cost increase by 10%, productivity loss of 20% and a drop in profit to 48 %. In case you strip and re-dye a fabric, then you are already incurring double the costs and you are in a huge loss!

It is estimated that only a 5% increase in RFT (from 75% to 80%) reduces the cost of inputs (chemicals, water and energy) by 15-20%!

To achieve a high RFT rate, variations in 3 areas need to be controlled:

• Lab to lab reproducibility
• Lab to bulk reproducibility
• Bulk to bulk reproducibility

3. Recovery and recycling of chemicals

The 3^rd factor for improving profitability is to recycle and re-use chemicals so as to reduce fresh consumption. Some examples of this are:

1. Recovery and Reuse of caustic soda from the mercerization bath
2. Recovery of Indigo from dyeing of denim
3. Recovery & Reuse of PVA Size
4. Reuse of softeners baths with reconstitution of required amount of softening agent in the reused bath for a fresh batch.
5. Reuse of spent baths of disperse dyeing, direct dyeing, vat dyeing (standing bath method) or metal complex dyeing of wool by collecting spent liquor in a separate tank after completion of dyeing, and making- up of the bath with required chemicals for circulation to a new batch for dyeing. Some investments in tanks, piping and metering devices will be required.

4. Reducing chemical usage through new technology and processes:

The Pad- Humidity- Fix process – or what is popularly known as E-Control process from Monforts – is an innovation that gives savings in chemical usage and other parameters in comparison to the Cold- Pad- Batch (CPB) batch dyeing method.

The table above is a case study between Cold –Pad- Batch and E-Control processes for a brown shade. You can see that there is not just less dyestuff used, but there is no need to use urea and silicate in the E- Control process. Also, the amount of caustic soda required for fixation of the reactive dyes is reduced by about 25%! Other indirect benefits include less dwell time, resulting in faster production.

Similarly, new machine manufacturing technology uses Low material to liquor Ratios (MLR) in dyeing machines that help to reduce water and chemicals consumption. The Then Air flow Synergy dyeing machines have been designed to reduce MLR to 1:2.5 for CO/PES and 1: 4 for CO fabrics. This lower use of water helps to reduce chemical and dyes consumption by 20- 30%.

Another innovative technique is the use of CLAYS in textile pre-treatment processes. Clays are inorganic, naturally- occurring volcanic material that have the ability to adsorb ions. The negatively charged plate- like structure of clay separates out in water and adsorbs metal ions and other impurities from the raw cotton. Clays can be used as a single auxiliary in cotton pre-treatment in place of sequestering agent, stabiliser for peroxide, scouring agent and lubricant. Thus, 4 chemicals that are normally used in cotton pre-treatment can be replaced by a single auxiliary, resulting in chemical savings as well as lower impact on the effluent treatment.