«EUROPEAN COMMISSION Integrated Pollution Prevention and Control (IPPC) Reference Document on Best Available Techniques for the Textiles Industry July 2003 ...»
Today, there are only a few mills that segregate high-loaded waste water streams, such as residual padding dyeing liquors and residual padding finishing liquors. Companies tend to apply these measures only when exceeding limits for COD, nitrogen or colour.
Conversely, it is more common to dispose separately of residual printing pastes. These pastes are disposed of in incineration plants or, in the case of reactive and vat printing pastes, in anaerobic digesters.
There are mills treating their waste water by flocculation/precipitation. The volume of sludge produced after dewatering (usually in chamber filter presses), including the water content (which is usually 60 – 65 %), is normally within the range 1 - 5 kg/m3 treated waste water. With a specific waste water flow of 100 - 150 l/kg, the amount of sludge to dispose of is 100 - 750 g/kg finished textiles [179, UBA, 2001].
4 TECHNIQUES TO CONSIDER IN THE DETERMINATION OFBAT
4.1 General good management practices 4.1.1 Management and good housekeeping Description The notes on management and housekeeping given here, although far from being exhaustive, attempt to point out some general principles and pollution prevention approaches that are almost universally applicable in textile mills.
Education/ training of employees Staff training is an important element of environmental management. All staff should understand clearly the precautions needed to avoid resource wastage and pollution. Training should be resource- (chemicals, fibres, energy, water), process- and machinery-specific.
Senior management should have a clearly expressed commitment to environmental improvement, preferably in the form of an environmental policy and an implementation strategy, made available to all staff.
Equipment maintenance and operations audit Machinery, pumps and pipework (including abatement systems) should be well maintained and free from leaks. Regular maintenance schedules should be established, with all procedures
documented. In particular, attention should be paid to the following areas:
· machinery checking: the most significant components of the machinery like pumps, valves, level switches and pressure and flow regulators should be included in a maintenance checklist · leak control: audits should be carefully conducted for broken and leaking pipes, drums, pumps and valves, not only in the water system but also from the oil heat transfer and chemicals dispensing systems in particular · filter maintenance: regular cleaning and checking · calibration of measuring equipment, such as chemicals measuring and dispensing devices, thermometers etc.
· thermal treatment units (e.g. stenters): all units should be regularly (at least once a year) cleaned and maintained. This should include cleaning deposits from the exhaust gas conducting system and from the intake system of the burner air inlet.
Chemicals storage, handling, dosing and dispensing Each chemical should be stored according to the instruction given by the manufacturer in the Material Safety Data Sheet.
All areas where chemicals are stored or spillages are likely to occur should be bunded and it should be impossible for spillage to enter surface waters or sewers. Toxic and dangerous chemicals should be stored separately. More detail on these issues will be found in the horizontal BREF on Storage (which was in preparation at the time of writing).
First aid facilities should be available and evacuation and emergency procedures in place and rehearsed regularly. Records of accidents and incidents (near-misses) must be kept.
Transfer of chemicals from storage to machine is often prone to leakage or spillage. Pumps and pipework used for transfer must be regularly inspected (see “Equipment maintenance” above)
and provisions should be made to ensure the safety of manual transfer (including appropriate training of workers, use of buckets with leak-proof lids, etc.) Accurate weighing, dispensing and mixing are fundamental to avoiding/minimising spillage in manual operation. However, an automated chemical dosing and dispensing system offers some important advantages over the manual method (better laboratory-to-dyehouse correlation;
minimises the chance of worker injury when handling hazardous chemicals; faster delivery times, etc.) Improved knowledge of chemicals and raw materials used The process inputs and outputs should be known and regularly monitored. This includes inputs of textile raw material, chemicals, heat, power and water, and outputs of product, waste water, air emissions, sludges, solid wastes and by-products (see Section 4.1.2).
Prescreening of incoming raw materials (fibres, chemicals, dyestuffs, auxiliaries, etc.) is of the utmost importance for pollution prevention. The supplier should take the responsibility for providing adequate information that enables the mill to make responsible environmental evaluation, even on proprietary products.
The detailed information provided to the finisher about textile raw material tends to be limited to the technical characteristics of the textile substrate. Information from the supplier should include also the kind and amount of preparation agents and sizing agents, amount of residual monomers, metals, biocides (e.g. ectoparasiticides for wool) present on the fibre. These substances/impurities are carried over into the process and account for a significant percentage of the pollution load from textile mills. Improved knowledge of the raw material will allow the manufacturer to prevent or at least control the resulting emissions.
Minimisation/optimisation of chemicals used
In general the overall strategy for the minimisation/optimisation of the chemicals used should
consider the following steps:
1. where it is possible to achieve the desired process result without the use of chemicals, then avoid their use altogether
2. where this is not possible, adopt a risk-based approach to selecting chemicals and their utilisation mode in order to ensure the lowest overall risk.
That said, possible measures of general applicability are:
· regularly revising the recipes in order to identify unnecessary chemicals (dyes, auxiliaries) so that they can be avoided · giving preference in the selection of auxiliaries and chemicals to products with a high degree of biodegradability/ bioeliminability, low human and ecological toxicity, low volatility and low smell intensity (see Sections 4.3.1 and 4.3.2) · optimising the process by improving the control of process parameters such as temperature, chemical feed, dwell times, moisture (for dryers), etc.
· using high-quality water (where needed) in wet processes in order to avoid/reduce the use of chemicals to prevent side effects caused by the presence of impurities · avoiding/ minimising any kind of surplus of applied chemicals and auxiliaries (e.g. by automated dosing and dispensing of chemicals) · optimising scheduling in production (e.g. in dyeing: dyeing dark shades after pale shades reduces water and chemicals consumption for machine cleaning) · giving preference to low add-on devices for chemicals · re-using mother-baths whenever possible · recovering vapour during delivery of volatile substances
· filling of tanks with volatile compounds using the following precautions:
- use of vapour balancing lines that transfer the displaced vapour from the container being filled to the one being emptied
- bottom loading to avoid splashing (for larger tanks).
Use of water and energy:
In order to develop waste minimisation options in a process, a detailed understanding of the plant wastes and operations is required. In particular, optimal use of water and energy should start from monitoring of water, heat and power consumption of sub-units of the process and characterisation of the facility waste streams. This general, but fundamental, approach is explained in Section 4.1.2.
Using this improved knowledge of the process, a number of low-technology measures can be identified. A first group of measures applicable to wet processes (in which water and energy consumption are often related because energy is used to a great extent to heat up the process
· installation of flow control devices and automatic stop valves which link the main drive mechanism of the range to the water flow (e.g. on continuous washers – Section 4.9.2) · installation of automatic controllers to facilitate accurate control of fill volume and liquor temperature (e.g. batch dyeing machines) · substitution of overflow-flood rinsing method (in batch processes) in favour of drain and fill or other methods (e.g. smart rinsing) based on optimised process control (see Section 4.9.1) · optimisation of scheduling in production (e.g. in dyeing: dyeing dark shades after pale shades reduces water and chemicals consumption for machine cleaning; in finishing: proper scheduling minimises machine stops and heating-up/cooling down steps) · adjustment of processes in pretreatment to quality requirements in downstream processes (e.g. bleaching is often not necessary if dark shades are produced) · combination of different wet treatments in one single step (e.g. combined scouring and desizing, combined scouring/desizing and bleaching – an example is given in Section 4.5.3) · water re-use (e.g. re-use of final rinsing baths, dye bath re-use, use water for pre-washing carpets in after-washing, countercurrent flows in continuous washing– see Section 4.6.22) · re-use of cooling water as process water (and also for heat recovery).
Note that whenever water is re-used/ recycled it is important to discriminate between water usage and water consumption of the process. When water is re-used in the process the overall water consumption naturally reduces.
A second group of options specifically focused on energy savings is:
· heat-insulation of pipes, valves, tanks, machines (see Section 4.1.5) · optimising boiler houses (re-use of condensed water, preheating of air supply, heat recovery in combustion gases) · segregation of hot and cold waste water streams prior to heat recovery and recovery of heat from the hot stream.
· installing heat recovery systems on waste off-gases – an example is given in Section 4.8.1 · installing frequency-controlled electric motors · controlling moisture content in the circulating air and on the textile in stenters (see Section 4.8.1) · proper adjustment of drying/curing temperature and drying/curing time.
Management of waste streams
The following general measures can be identified:
· separate capture of high-loaded waste streams from low-concentrated effluent to allow more efficient treatment · separate collection of unavoidable solid waste · reduction of packaging
· use of returnable containers · recycling of textile wastes (textile residues, spoilt work, raising, etc.).
Main achieved environmental benefits The main environmental advantages achievable by systematic performance of optimised housekeeping and management measures are savings in the consumption of chemicals, auxiliaries, fresh water and energy and the minimisation of solid waste and pollution loads in waste water and off-gas.
Workplace conditions can also be improved.
Operational data Vary with the type of measure considered. Cross-references to fuller information about some techniques are given above.
Cross-media effects None believed likely.
Applicability Most of the described methods are cheap and do not require investment in new equipment, although the immediate applicability of some of the techniques in existing mills may be limited by considerations of space, logistics etc. and the need for major structural modifications.
Particularly, space availability may be an issue in some existing plants if implementing measures such as the optimisation of boiler houses and the installation of heat recovery systems for off-gases [311, Portugal, 2002].
Some measures, such as the installation of automated dosing systems and process control devices, may be expensive, depending on how sophisticated they are.
The success of management and good housekeeping measures is largely dependent on the commitment and organisational skills of management. Tools such as EN ISO 9000 ff, EN ISO 14001 and EMAS will support this approach. Information and communication are required at company level and within the whole supply chain.
The described measures enable improved operational reliability and reproducibility, which is economically beneficial. The main economic benefits are savings in the consumption of energy, fresh water, chemicals, and in the cost of waste water, off-gas cleaning and discharge of solid waste.
Driving force for implementation Cost savings, improvement of operational reliability, improved environmental performance and compliance with legislation are the main reasons for implementing good general management / good housekeeping.
Reference plants Various textile finishing mills in Europe have implemented good general management practices to improve their environmental performance and are working in accordance with good housekeeping principles.
Reference literature [192, Danish EPA, 2001], [179, UBA, 2001], [51, OSPAR, 1994], [77, EURATEX, 2000], [11, US EPA, 1995], [32, ENco, 2001], [187, INTERLAINE, 1999].
4.1.2 Input/output streams evaluation/inventory Description All environmental problems are directly linked with input/output streams. In the interests of identifying options and priorities for improving environmental and economic performance, it is therefore vital to know as much as possible about their quality and quantity.
Input/output stream inventories can be drawn up on different levels. The most general level is an annual site-specific overview.
Figure 4.1 indicates the relevant input/output streams.
Starting from the annual values, specific input and output factors for the textile substrate can be calculated (e.g. litre of water consumption/kg processed textiles or g of COD in waste water/kg processed textiles etc.).
Although these factors have their limitations, they allow preliminary comparisons with other sites or similar processes and they provide a baseline against which to start tracking on-going consumption and emission levels. Available data for different categories of waste water are presented in Chapter 3.
Figure 4.1: Scheme for annual input/output overview at site level [179, UBA, 2001] The systematic listing and evaluation of applied chemicals (dyestuffs and pigments, textile auxiliaries and basic chemicals) is very important for identifying critical compounds.
It is therefore recommended that eight forms be used, one for each of the following classes (see
example in Table 4.1):
· auxiliaries and finishing agents for fibres and yarns · pretreatment agents · textile auxiliaries for dyeing and printing · finishing assistants · technical auxiliaries for multipurpose use in the textile industry · textile auxiliaries not mentioned in the Textile Auxiliaries Buyer’s Guide “Melliand/TEGEWA, 2000” · basic chemicals (all inorganic compounds, all aliphatic organic acids, all organic reducing and oxidising agents, urea) · dyestuffs and pigments.
The first six categories are identical with Textile Auxiliaries Buyer’s Guide.
The following table shows an example form for dyeing and printing.
The listing allows a first rough assessment of the applied chemicals and a calculation of COD input to the process. The information on biological degradation/elimination is the basis for the selection of products with higher biodegradability/bioeliminability. The full picture, however, can only be had by assessing each of the ingredients of the commercial formulations used. In addition, the information on biological degradation/elimination often has to be critically questioned with respect to the properties of chemicals and the testing methods.