«EUROPEAN COMMISSION Integrated Pollution Prevention and Control (IPPC) Reference Document on Best Available Techniques for the Textiles Industry July 2003 ...»
There are a number of lists and classification tools for chemicals. Modes of operation that ensure the lowest overall risk include techniques such as closed-loops and the in-loop destruction of pollutants. Of course, it is essential that due recognition be given to relevant Community legislation.
Following these principles, a number of detailed BAT conclusions arise in particular for surfactants, complexing and antifoaming agents. More details are found in Chapter 5.
Selection of incoming fibre raw material It is recognised that knowledge of the quality and quantity of substances (e.g. preparation agents, pesticides, knitting oils) applied on the fibre during the upstream processes is essential to enable the manufacturer to prevent and control the environmental impact resulting from these substances. BAT is to seek collaboration with upstream partners in the textile chain in order to create a chain of environmental responsibility for textiles. It is desirable to exchange information on the type and load of chemicals that are added and remain on the fibre at each
stage of the product’s life cycle. A number of BAT were identified for different raw materials:
· man-made fibres: BAT is to select material treated with low-emission and biodegradable/ bioeliminable preparation agents · cotton: the main issues are the presence of hazardous substances such as PCP and the quality and quantity of sizing agents used (selection of material sized with low add-on techniques and high-efficiency bioeliminable sizing agents). Preference should be given to organically grown cotton when market conditions allow · wool: emphasis is given to using available information and to encouraging collaboration initiatives between competent bodies in order to avoid processing wool contaminated with OC pesticides and minimise at the source any legally used sheep ectoparasiticides. The selection of wool yarn spun with biodegradable spinning agents instead of formulations based on mineral oils and/or containing APEO is also part of BAT.
All measures assume that the fibre raw materials for textile processing are produced with some sort of quality assurance scheme, so that the finisher can get the appropriate information about the types and amounts of contaminants.
Water & energy management Water and energy savings are often related in the textile industry because the main use of energy is to heat up the process baths. BAT starts from the monitoring of water and energy consumption in the various processes along with improved control of process parameters. BAT includes the use of machinery with reduced liquor ratio in batch processing and low add-on techniques in continuous processing, applying the latest techniques to improve washing efficiency. BAT is also to investigate possibilities for water re-use and recycling by a systematic characterisation of quality and volume of the various process streams.
Wool scouring with water BAT is to use recovery loops for grease and dirt. BAT-associated values for water consumption are 2 to 4 l/kg of greasy wool for medium and large mills (15000 tonnes/year of greasy wool) and 6 l/kg for small mills. Associated values for grease recovery range between 25 and 30 % of the grease estimated to be present in the scoured wool. Likewise, BAT-associated values for energy consumption are 4 - 4.5 MJ/kg greasy wool processed, comprising approximately
3.5 MJ/kg thermal energy and 1 MJ/kg electrical energy. However, due to the lack of data it is
not possible to define whether the above-mentioned BAT associated values for water and energy consumption are also applicable to extra-fine wool (fibre diameter typically in the order of 20µm or less).
Wool scouring with organic solvent Scouring with organic solvent is determined as BAT, provided that all measures are taken to minimise fugitive losses and prevent any possible contamination of groundwater arising from diffuse pollution and accidents. Details about these measures are described in Section 188.8.131.52.
TEXTILE FINISHING AND CARPET INDUSTRYPretreatment Removing knitting lubricants from fabric
BAT is to do one of following:
· select knitted fabric that has been processed using water-soluble and biodegradable lubricants instead of the conventional mineral oil-based lubricants (see Section 4.2.3).
Remove them by water washing. With knitted fabrics made of synthetic fibres the washing step needs to be carried out before thermofixation (to remove the lubricants and avoid them being released in the form of air emissions) · carry out the thermofixation step before washing and treat the air emissions generated from the stenter frame by dry electrofiltration systems that allow energy recovery and separate collection of the oil. This will reduce the contamination of the effluent (see Section 4.10.9) · remove the non-water soluble oils using organic solvent washing. The requirements described in Section 184.108.40.206 are then taken, along with provisions for the in-loop destruction of the persistent pollutants (e.g. by advanced oxidation processes). This will avoid any possible contamination of groundwater arising from diffuse pollution and accidents. This technique is convenient when other non water-soluble preparation agents, such as silicone oils, are present on the fabric.
BAT is to do one of the following:
· select raw material processed with low add-on techniques (e.g. pre-wetting of the warp yarn, see 4.2.5) and more effective bioeliminable sizing agents (see 4.2.4) combined with the use of efficient washing systems for desizing and low F/M waste water treatment techniques (F/M 0.15 kg BOD5/kg MLSS·d, adaptation of the activated sludge and temperatures higher than 15 °C – see 4.10.1) to improve the bioeliminability of the sizing agents · adopt the oxidative route when it is not possible to control the source of the raw material (see Section 220.127.116.11) · combine desizing/scouring and bleaching in one single step, as described in Section 4.5.3.
· recover and re-use the sizing agents by ultrafiltration as described in Section 4.5.1.
BAT is to:
· use hydrogen peroxide bleaching as preferred bleaching agent combined with techniques for minimising the use of hydrogen peroxide stabilisers, as described in Section 4.5.5, or using biodegradable/bioeliminable complexing agents described in Section 4.3.4 · use sodium chlorite for flax and bast fibres that cannot be bleached with hydrogen peroxide alone. A two-step hydrogen peroxide-chlorine dioxide bleaching is the preferred option. It must be ensured that elemental chlorine-free chlorine dioxide is used. Chlorine-free chlorine dioxide is produced using hydrogen peroxide as the reducing agent of sodium chlorate (see Section 4.5.5) · limit the use of sodium hypochlorite only to cases in which high whiteness has to be achieved and to fabrics that are fragile and would suffer depolymerisation. In these special cases, to reduce the formation of hazardous AOX, sodium hypochlorite bleaching is carried out in a two-step process in which peroxide is used in the first step and hypochlorite in the second. Effluent from hypochlorite bleaching is kept separate from the other streams and mixed effluents in order to reduce formation of hazardous AOX.
BAT is to either:
· recover and re-use alkali from mercerising rinsing water as described in Section 4.5.7 · or re-use the alkali-containing effluent in other preparation treatments.
Dyeing Dosage and dispensing of dye formulations
BAT is to do all the following:
· reduce the number of dyes (one way to reduce the number of dyes is by using trichromatic systems) · use automated systems for dosage and dispensing of dyes, only considering manual operation for dyes that are used infrequently · in long continuous lines where the dead volume of the distribution line is comparable with the volume in the padder, give preference to decentralised automated stations that do not premix the different chemicals with the dyes before the process and that are fully automatically cleaned.
General BAT for batch dyeing processes
BAT is to:
· use machinery fitted with: automatic controllers of fill volume, temperature and other dyeing cycle parameters, indirect heating & cooling systems, hoods and doors to minimise vapour losses · choose the machinery that is most fitted to the size of the lot to be processed to allow its operation in the range of nominal liquor ratios for which it is designed.
Modern machines can be operated at approximately constant liquor ratio whilst being loaded at a level as low as 60 % of their nominal capacity (or even 30 % of their nominal capacity with yarn dyeing machines) (see Section 4.6.19) · select new machinery according as far as possible to the requirements described in Section 4.6.19:
Ø low- or ultra-low liquor ratio Ø in-process separation of the bath from the substrate Ø internal separation of process liquor from the washing liquor Ø mechanical liquor extraction to reduce carry-over and improve washing efficiency Ø reduced duration of the cycle.
· substitute overflow-flood rinsing method in favour of drain and fill or other methods (smart rinsing for fabric) as described in Section 4.9.1 · re-use rinse water for the next dyeing or reconstitution and re-use the dye bath when technical considerations allow. This technique (see Section 4.6.22) is easier to implement in loose fibre dyeing where top-loading machines are used. The fibre carrier can be removed from the dyeing machine without draining the bath. However, modern batch dyeing machines are equipped with built-in holding tanks allowing for uninterrupted automatic separation of concentrates from rinsing water BAT for continuous dyeing processes Continuous and semi-continuous dyeing processes consume less water than batch dyeing, but highly concentrated residues are produced.
BAT is to reduce losses of concentrated liquor by:
· using low add-on liquor application systems and minimising volume capacity of the dip trough when using pad dyeing techniques · adopting dispensing systems where the chemicals are dispensed on-line as separate streams, being mixed only immediately before being fed to the applicator · using one of the following systems for dosing the padding liquor, based on measurement of
the pick up (see 4.6.7):
Ø measure the amount of dyeing liquor consumed by reference to the quantity of processed fabric (length of the fabric multiplied by its specific weight); the resulting values are automatically processed and used for the preparation of the next comparable batch Ø use the rapid batch dyeing technique, where rather than being prepared for the whole batch before starting the dyeing batch, the dyestuff solution is prepared just in time, in several steps, based on on-line measurement of the pick up. This second technique is preferred when economic considerations allow (see 4.6.7) · increase washing efficiency according to the principles of counter-current washing and reduction of carry-over described in Section 4.9.2.
PES & PES blends dyeing with disperse dyes
BAT is to:
· avoid the use of hazardous carriers by (in order of priority):
Ø using non-carrier dyeable polyester fibres (modified PET or PTT-type) as described in Section 4.6.2, when product market considerations allow Ø dyeing in HT conditions without use of carriers. This technique is not applicable to PES/WO and elastane/WO blends Ø substituting conventional dye carriers with compounds based on benzylbenzoate and Nalkylphthalimide, when dyeing WO/PES fibres (see Section 4.6.1) · substitute sodium dithionite in PES aftertreatment, by applying one of the two proposed
techniques (as described in Section 4.6.5):
Ø replace sodium dithionite with reducing agent based on sulphinic acid derivatives. This should be combined with measures in order to ensure that only the strict amount of reducing agent needed to reduce the dyestuff is consumed (e.g. by using nitrogen to remove oxygen from the liquor and from the air in the machine) Ø use of disperse dyes that can be cleared in alkaline medium by hydrolitic solubilisation instead of reduction (see Section 4.6.5) · use optimised dye formulations that contain dispersing agents with high degree of bioeliminability as described in Section 4.6.3.
Dyeing with sulphur dyes
BAT is to (see 4.6.6):
· replace conventional powder and liquid sulphur dyes with stabilised non-pre-reduced sulphide-free dyestuffs or with pre-reduced liquid dye formulations with a sulphide content of less than 1 % · replace sodium sulphide with sulphur-free reducing agents or sodium dithionite, in that order of preference · adopt measures to ensure that only the strict amount of reducing agent needed to reduce the dyestuff is consumed (e.g. by using nitrogen to remove oxygen from the liquor and from the air in the machine) · use hydrogen peroxide as preferred oxidant.
Batch dyeing with reactive dyes
BAT is to:
· use high-fixation, low-salt reactive dyes as described in Sections 4.6.10 and 4.6.11 · avoid the use of detergents and complexing agents in the rinsing and neutralisation steps after dyeing, by applying hot rinsing integrated with recovery of the thermal energy from the rinsing effluent (see Section 4.6.12).
Textiles Industry xv Executive Summary Pad-batch dyeing with reactive dyes BAT is to use dyeing techniques that perform at equivalent levels to those described in Section 4.6.13. The technique described is more cost effective than pad-batch dyeing in terms of total processing costs, but the initial capital investment in switching to the new technology is significant. However, for new installations and those seeking to replace equipment the cost factor is not so significant. In all cases, BAT is to avoid the use of urea and to use silicate-free fixation methods (see Section 4.6.9).
BAT is to:
· substitute chrome dyes with reactive dyes or, where not possible, use ultra-low chroming
methods that fulfil all the following requirements as defined in Section 4.6.15:
Ø an emission factor of 50 mg chromium per kg of wool treated is achieved, which corresponds to a chromium concentration of 5 mg/l in the spent chroming bath when a 1:10 liquor ratio is used Ø no chromium (VI) is detectable in the waste water (using a standard method able to detect Cr VI at concentrations 0.1 mg/l) · ensure minimum discharge of heavy metals in the waste water when dyeing wool with metal complex dyes. BAT associated values are emission factors of 10 - 20 mg/kg of treated wool, which correspond to 1 - 2 mg/l of chromium in the spent dye bath when a 1:10 liquor
ratio is used. These performances can be achieved by:
Ø using auxiliaries that enhance dye uptake like, for instance, the process described in Section 4.6.17 for loose wool and tops Ø using pH control methods to maximise final bath exhaustion for other make-ups · give preference to a pH-controlled process when dyeing with pH-controllable dyes (acid and basic dyes) so that level dyeing is obtained with maximum exhaustion of dyes and insect resist agents and minimum use of organic levelling agents (see Section 4.6.14).
Process in general
BAT is to:
· reduce printing paste losses in rotary screen printing by:
Ø minimising the volume of printing paste supply systems (see 4.7.4) Ø recovering printing paste from the supply system at the end of each run by adopting the technique described in Section 4.7.5 Ø recycling residual printing paste (see Section 4.7.6)
· reduce water consumption in cleaning operations by a combination of (see Section 4.7.7):