«EUROPEAN COMMISSION Integrated Pollution Prevention and Control (IPPC) Reference Document on Best Available Techniques for the Textiles Industry July 2003 ...»
Data presented in Figure 3.14 also illustrate typical permethrin emissions from a site operating with the conventional means of mothproofing, in which mothproofing is carried out in loose fibre dyeing. The resultant yarn is subsequently scoured to remove lubricant, contaminating the scour liquors with mothproofer. This process is no longer commonplace in the UK, where the majority of manufacturers using this production route are obliged to apply mothproofing agent from a special low-volume application bowl at the end of the scouring line, in order to meet local waste water emission limits.
Reference Sites A and B use the highest proportions of afterchrome dyes, which is reflected by mill effluent loads in the range of 53 – 66 g/tonne of dyed fibre. Note that loads are derived from effluent parameters and total dyed fibre and therefore do not represent loads from individual dyeings carried out with these materials, which are obviously higher (approximately 90 g/tonne fibre for chrome dyes and 10 g/tonne fibre for complex dyes).
Organochlorine pesticides and organophosphorus & synthetic pyrethroid ectoparasiticides Meaningful quantitative data on the concentrations of the organochlorine pesticides present in mill effluent are difficult to obtain, not least because the levels present are often below the lower limit of detection of the analytical procedure, but also because the occurrence of these compounds on wool is intermittent and they therefore occur in effluents in an unpredictable pattern.
The reported data have been calculated from raw fibre consumption and data relating to the partition of the different pesticides between waste water and the fibre for different wet processing sequences. Fibre consumption is identified by country of origin and the initial pesticide content calculated using data from the ENco wool & hair pesticide database. As an example, annual average pesticide content of scoured wool processed at six reference sites is reported in Table 3.52.
Table 3.52: Annual average pesticide content of scoured wool processed at six reference sites The annual pesticide mass released in the effluent is then calculated by applying a waste waterfibre partition coefficient for each of the wet processes used.
These coefficients were determined from trials with fibre selected to have a high initial pesticide loading, thus ensuring analytical detection at each processing stage. The same approach is also applied for OP and SP pesticides. Partition values for the most relevant OC, OP and SP pesticides are reported in Figure 3.13.
Recent studies indicate that individual OPs, (propetamphos, diazinon and chlorfenvinphos) and the SP cypermethrin behave differently when subjected to the wet treatments common in carpet fibre processing [32, ENco, 2001].
In high-temperature dyeing processes these compounds partition between the dye liquor and the fibre in ratios which approximate to their relative water solubility, thus cypermethrin (solubility
0.009mg/l) is generally present at lower concentrations than propetamphos (solubility 110mg/l).
Diazinon behaves somewhat differently and is degraded at the pH values used in wool dyeing, being present neither on the fibre nor in the effluent on completion of dyeing. This observation has been made only recently (ENco, 2000, unpublished results) but explains why many dyehouse effluents appear to contain appreciably less diazinon than propetamphos when the average content of scoured wool is the reverse.
Dyeing also causes hydrophobic pesticides to migrate from the surface into the micro-structure of the wool fibre. Scouring ecru (undyed) yarn thus releases more of these compounds into the effluent than does the scouring of yarn spun from previously dyed fibre.
Where they can be measured, emissions of OC pesticides fall in the range 0.001 - 0.025 g/t of processed wool, reflecting the background environmental contamination responsible for their presence on the fibre. The OP and SP ectoparasiticides are present at higher levels as a result of their registered use as sheep medicines.
Table 3.53: Overview of emission and consumption levels for four typical carpet yarn dyehouses Water & energy consumption Among the four sites analysed, data on water and energy consumption are available only for Sites H, K and L.
Nevertheless they are useful to represent a range of yarn dyeing processes, resulting in quite different water requirements. Both sites H and K pre-scour yarn in hank form and hank dye in Hussong type machines (L.R. 1:15). On Site H, the bulk of production is not rinsed following dyeing, while on Site K the reverse is true. In the former case water consumption amounts to 22m3/tonne of product while on the latter site 53m3/tonne is required.
Site L dyes yarn on packages (L.R. 1:12), without pre-scouring; in this case the water and energy requirements are significantly lower than for hank dyeing.
The considerations outlined for loose fibre dyeing, regarding the meaning of the total water and energy consumption values reported in this report with respect to the corresponding theoretical requirements, are also valid for yarn dyeing.
The theoretical energy requirements for yarn dyeing can therefore be defined as follows:
· yarn package dyeing (heating 10 kg of water per kg of textile): 4.2 GJ/tonne · hank dyeing (heating 15 kg of water per kg of textile): 6.3 GJ · yarn drying (water content when entering the dryer: 0.5 kg/kg textile): 1.3 GJ/tonne.
The total theoretical energy requirement is, therefore, 5.5 and 7.6 GJ/tonne of textile for package and hank dyeing respectively.
The energy requirements of individual plants are two to three times higher than the above figures for the same reasons as those mentioned earlier for loose fibre dyeing. The wide range of values also reflects the types of processes employed on each site. Sites H and K operate hank dyeing equipment and pre-scour the yarn before dyeing. Conversely, Site L operates with package dyeing equipment at a liquor ratio closer to that employed in loose fibre dyeing. In addition, Site L does not pre-scour the yarn, but simply carries out dyeing in the presence of the lubricant, which is specially selected not to interfere with dyeing (this is a not very common process).
Data from the survey record only total energy consumption in wet processing and it was not possible to estimate reliably the proportions attributable to dyeing and drying. However, values are available from other studies (Table 3.54) for hank scouring, dyeing and drying processes and package dyeing of textiles. These sources typically indicate an overall energy requirement of between 17 and 28 GJ/tonne of textile for the hank dyeing route and 5 to 18 GJ/tonne for package dyeing. The values recorded in the industry survey fall within this range, so can be taken as representative of current industry practice. In the majority of cases, approximately 75 % of the energy use arises from scouring and dyeing and 25 % from the drying operations.
Table 3.54: Literature values for practical energy requirements in yarn dyeing Chemical Oxygen Demand The reported figures record the COD load of the final effluent.
It is possible, however, to estimate that the proportion of COD arising from the scouring process accounts for up to 80 % of the total. The total load from scouring is not distributed evenly between scour bowls and, in most installations, bowls 1 and 2 contain up to 95 % of the residues.
In the yarn dyeing sector, acid dyes predominate due to the requirement for level dyeing and may account for up to 90 % of total usage on any given site. Individual manufacturers may dye yarn from specific market segments that require a higher degree of fastness and the use of metal-complex and reactive dyes. The use of chrome dyes is normally restricted to the production of black and navy shades and the proportion of these dyes is typically no more than
5 % of total usage. Among the dyeing auxiliaries consumed, a significant percentage is represented by polyamide reserving agents.
In assessing the COD load in yarn dyeing effluents, it has to be pointed out that, besides the chemicals and auxiliaries used by the finisher, fibrous raw materials carry an additional amount of organic contaminants into the process stream. Synthetic yarn, in particular, contains both the synthetic fibre spin finish and spinning lubricants applied to aid mechanical processing in the mill. These substances are largely removed during the first wet process to which the fibre is subjected, thus contributing to a proportion of the chemical oxygen demand present in waste water.
Table 3.55 indicates the approximate loading of COD-contributing compounds present on raw materials entering the production chain.
The figures were generated by subjecting samples of the raw material to a simple aqueous extraction procedure to simulate the first wet process.
Oxygen-demanding chemicals present on spun yarn prior to scouring are related to the quality of the raw materials, as described above, and to the quantity and nature of the spinning lubricant applied by the spinner. Residual COD carried forward from yarn scouring into dyeing reflects the efficiency of the scouring process. Inevitably the COD attributable to this source varies widely.
Table 3.55: Concentration of compounds present on raw fibre, which contribute to the waste water load Synthetic pyrethroids from mothproofer Emission levels associated with yarn dyeing are generally a function of dye bath pH and auxiliary usage.
Dyeing under the strongly acidic conditions associated with the use of level dyeing acid dyes produces the lowest feasible residues, while dyeing under the more neutral conditions necessary when using metal-complex dyes will produce significantly higher residues.
Emission factors can vary from 0.7 g/tonne of yarn, under acid levelling conditions, to
9.2 g/tonne when dyeing at pH4.5 with metal-complex dyes. Moreover, some dyeing auxiliaries, particularly levelling agents, can exert a significant retarding action with respect to mothproofer uptake.
Of the companies involved in the survey, Site H shows a higher permethrin emission factor (0.24 g/tonne) than Site J (0.035 g/tonne). The difference cannot be attributed to the classes of dyestuffs used, however, because the two companies operate in similar conditions, both using predominantly acid dyes. The difference is attributable to the fact that Site H mothproofs all production with permethrin-based agent, while Site J uses a mixture of agent types and does not mothproof all production in dyeing.
Site L does not use permethrin-based mothproofers and residues in its effluent must, therefore, arise from the processing of previously contaminated fibre.
Metals Residual metals in the waste water invariably mirror dyestuff usage patterns. In particular, the levels of chromium reflect the usage of chrome dyes. In yarn dyeing the use of acid and metalcomplex dyes is predominant. The emission levels of chromium are therefore not as high as for loose fibre dyeing. The highest emission factor corresponds to Site L, where metal-complex and chrome dyes (in lower percentage) account for 60 % of the total amount of dyestuffs consumed.
Organochlorine pesticides and organophosphorus & synthetic pyrethroid ectoparasiticides The considerations outlined for loose fibres are also valid for yarn dyehouses. The partition factors for yarn dyeing processes are reported in Figure 3.13
3.4.2 Integrated carpet manufacturing companies Table 3.56 reports data for waste water emissions from two carpet finishing mills. Here, specific consumption is not related to kg but to m2. There is limited information available for the finishing of carpets in piece form. Therefore the examples in the table are intended to give only a preliminary insight [179, UBA, 2001].
Table 3.56: Concentration values and textile substrate-specific emission factors for waste water from two carpet finishing mills Both sites are integrated plants where dyeing, printing and back-coating are carried out.
TFI 1 dyes only in discontinuous, whereas TFI 2 is one of the few plants dyeing with the Carpet-ORoll method. Both sites use the rotary printing technology.
As for waste water flow, the exhaust dyeing section accounts for the highest share (about 80 %), followed by the printing section (18.5 %). The waste water from the application of latex (this process is carried out only in TFI 1) results from cleaning of the application equipment and accounts for about 1.5 % of the discharged volume. This effluent is usually treated by flocculation/precipitation, resulting in considerable amounts of sludge to be disposed of.
The applied chemicals are grouped as dyestuffs, textile auxiliaries and basic chemicals. The
values from the two mills are as follows:
For one mill the sum of textile auxiliaries and basic chemicals is 55.2 g/m2.
The specific consumption of electricity of the two mills is 0.9 and 1.3 kWh/m2. The consumption of oil or natural gas is not available.
126.96.36.199 Analysis of some relevant specific processes for carpet manufacturing mills There is no detailed information available that can provide a realistic picture of emission and consumption levels for specific processes in this category of mills. The only process-specific data presented in this section regard air emissions from carpet backing lines. Data are based on measurements carried out in a sample of carpet manufacturing mills over the period 1996 - 2001.
Table 3.57 gives an overview of the composition of the off-gases from two typical carpet backing lines (textile backing and foam backing).
As Table 3.58 shows the main pollutants found in the exhaust air are VOC, measured as total organic carbon.
Hazardous substances such as 1,3 butadiene and 4-vinyl-1-cyclohexene can be emitted from latices. However, nowadays their concentration is low, especially the 1,3 butadiene content which is normally below 1 mg/kg.
Ammonia, which is mainly used as stabiliser for the latex, is also often found in the emissions.
Latices with only very small amounts of ammonia or even ammonia-free latices are available on the market today.
Table 3.57: Overview of the composition of the off gases of two typical carpet backing lines (textile backing and foam backing).
Analysis was performed by GC/MS
3.5 General issues concerning odour nuisances in the textile industry Some processes in the textile industry are often accompanied by odour emissions.
Odour-intensive substances and typical ranges for odour concentrations are summarised in Table 3.59 and Table 3.60.
Table 3.60: Typical examples of odour concentrations in some textile processes (OU: odour unit)
3.6 General issues concerning solid & liquid wastes generated in the textile industry In textile finishing industries, many different solid and liquid wastes are generated and have to be disposed of. Some of them can be recycled or re-used, whereas others are incinerated or landfilled. There are also some wastes which (in a few cases) are treated in anaerobic digesters.
Many of these wastes are not specific to the textile finishing industry. A distinction is therefore made here between solid wastes that are specific to this sector and those that are not (see Table 3.61).
Waste in need of high control
- Waste from oil/water separators
- Halogenated organic solvents
- PCB-containing condensers Source: [179, UBA, 2001] Table 3.61: Solid and liquid wastes from textile industry Usually, most of the textile waste is recycled.