1. wool scouring environment issues


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1. wool scouring environment issues

  1. 1. 2 APPLIED PROCESSES AND TECHNIQUES15.The textile chain begins with the production or harvest of raw fibre. The basic steps inthis chain are schematically represented in the following diagram and will be described inthis chapter.Figure 2.! : General diagramme of processes in textile industry
  2. 2. 2.1.9 WoolComposition of wool Wool is an animal hair from the body of sheep. This hair is normallysheared once, or sometimes twice, a year and its quality and quantity varieswidely, depending on the breed of sheep and its environment. Wool is amember of a group of proteins known as keratin, also found in horns, nails,etc. In addition to wool fibre, raw wool contains:• Natural impurities - Wool grease 2-25% of greasy wool weight - - Suint (dried perspiration) 2 - 12 % of greasy wool weight - - Dirt 5-45% of greasy wool weight - • Residues of insecticides, acaricides or insect growth regulators used as veterinary medicines to protect sheep from ectoparasites, such as lice, mites, blowfly, etc. The percentage of the above-mentioned components may vary widely depending on the origin of wool. For example, fine wool from merino sheep, used mainly in apparel, typically contains 13 % wool grease, whereas coarser wool of the types used for carpets contains an average of
  3. 3. about 5 % grease. The clean Fibre content of raw wool usually lies within the 60 to 80 % range, but may vary from 40 to 90 %. Wool grease is insoluble in water, but soluble in non-polar solvents such as dichloromethane or hexane. Refined wool grease is a valuable by- product. Suint is water-soluble material arising from the secretion of the sweat glands in the skin. Suint is soluble in polar solvent such as water and alcohol. Dirt can include a variety of materials such as mineral dirt, sands, clay, dust and organic materials. %•Keratine 33•Dirt 26•Suint 28 (Dried perspiration)•Fat 12•Burrs 2-10 (Dried vegetable matter)•Mineral matter 1•Colouring matter 0.5-Ectoparasiticideshave important implications for the discharge of raw woolscouring effluent and disposal of the sludge generated bythe treatment of the effluent. The chemicals known to bepresent in raw wool inciude:• Organochlorine insecticides (OCs) --yHexachlorocyclohexane (Imdane)Dieldrin- DDT• Organophosphorotis insecticides (OPs)– Diazinon– - Propetamphos– - Chlorfenvinphos– Chlorpyriphos– Dichlorfenthion20 • Synthetic pyrethroids insecticides (SPs)
  4. 4. - Cypermethrin - Deltamethrin - Fenvalerate Flumethrin - - Cyhalothrin - • Insect growth regulators (IGRs) - - Cyromazine - Dicyclanil - - Difilibenzliron - TriflumuronThe organochlorines are hazardous due to their persistenceand bioaccumulity. They are thus likely to have long-rangeeffects (in terms of both distance from the source and timeafter release). y-Hexachlorocyclohexane (also called lindane)is the most toxic (and also the most active as pesticide) ofthe hexaclorocyclohexane isomers (alpha and beta-HCHs).The technical crude product contains alpha- and beta-HCH,the beta-isomer being the most persistent. Lindane and DDTcompounds are well-studied substances with demonstratedendocrine disrupting capacity. The synthetic pyrethroidinsecticides show high aquatic toxicity (predicted no-effectconcentration for cypermethrin is estimated at 0.0001 ug/l,while the corresponding value for the OPs diazinon andpropetamphos is 0.01 ug/l - UK environmental qualitystandards expressed as annual average). Organophosphateshave lower aquatic toxicity than synthetic pyrethroids andare less persistent than organochlorines. Nevertheless theyhave high human toxicity (problems may therefore arise forexample, for dyers with steam volatile OPs) [279, L.Bettens. 3001]. All major grower countries have banned theuse of organochlorine pesticides for sheep treatment, butthere is evidence that wool from some former Soviet UnionStates and South America contain lindane at detectableconcentrations. This would suggest that either their grazingis heavily contaminatd or that this compound continues tobe used occasionally for sheep treatment againstectoparasites.
  5. 5. Wool from the majority of grower nations contains residualsheep treatment medicines which are used legally to controlinfestations of lice. ticks and mites. These materials may beorganophosphates, typically diazinon. propetamphos andtrans-chlorfenvinphos, synthetic pyrethroids, typicallycyperinethrin and insect growth regulators such ascyromazine. The incidence of these materials on wool isvariable and depends on the permitted legal use pattern ineach country.Manufacturers can use a database containing quantitativeinformation on the OC, OP and SP content of wool frommajor producing countries. ENco maintains one suchdatabase. Manufacturers use these data to avoid processingwool from suspect sources. The system is of immediatebenefit to manufacturers who purchase and process woolfrom known sources. Commission processors of either loosefibre or yarn may not be aware of the origin of the Fibrethey are processing and so find it more difficult to controltheir raw material inputs using this approach. Moreinformation regarding ectoparasiticides is reported in Section2.3.1 where the wool sourcing process is discussed.Wool scouringEnvironment issues2.3.1.2 Environmental issues associated with woolscouring (with water) This section discusses theenvironmental issues associated with the overall scouringprocess including the treatment of the process effluent. Themain environmental issues associated with the wool scouringprocess arise from emissions to water, but solid waste andthe air emissions also need to be taken into account.Potential for pollution of waterThe removal of contaminants present on the raw fibre leadsto the discharge of an effluent in which the main pollutingcontributors are:
  6. 6. • highly concentrated organic material in suspension and insolution, along with dirt in suspension• micro-pollutants resulting from the veterinary medicinesapplied to protect sheep from external parasites.There are also detergents in the discharged water, whichcontribute to the increase of the chemical oxygen demand ofthe effluent.The detergent is recycled via the grease recovery/dirtremoval loop. As a result, low efficiency in this recoverysystem is associated with higher amounts of detergent in theeffluent.Compared to the chemical oxygen demand attributable towax, dirt etc.. the detergents can be considered minorcontributors to water pollution, but this is not the casewhen harmful surfactants such as alkylphenol ethoxylatesare used as detergents (for more detail on environmentalissues regarding detergents, see Section 8.1).As to the organic matter coming from wax and dirt.according to "Stewart. 1988" the COD of effluent and ofgreasy wool can be calculated using the following equation:COD(mg/kg) - (8267 x siiint(%)) + (30980 x oxidised gi-ease(%)) + (29326 x top grease(%)) + (6454 xdii-K%))+1536. Since the coefficients for top grease and oxidisedgrease in this equation are similar and since approximatelyequal quantities of top grease and oxidised grease arepresent in many wools, it is possible to combine the twogrease terms in the above equation as follows: COD (mg/kg)= (8267 x suint(%)) +(30153 x total gi-ease(%)) + (6454 xdirt(%)) + 1536 It is then possible to calculate the CODcontent of "typical" merino and crossbred wools: lop niv.iscisui1»xidisci.l urease which is readily separated lrom scourliquors by centriluging: oxidised ~reiise is les li-i.lropliol~i~and is ICc rea~.ih senarated Tclilvs Industry28.Cliiintir ". Merino wool: suint ~ 8 %, grease = 13 %: dirt =15 % COD - (8.267 x 8) +(30.153 x 13) +(6.454x15)
  7. 7. +1.536 = 556 g/kg greasy wool Crossbred wool: suint = 8"/(>. grease = 5 %: dirt = 15 % COD - (8.267 , 8)+(30.153 x 5) + (6.454 x 15)+1.536 = 315 g/kg greasywool.These high levels of oxygen-depleting substances must beremoved from the effluent before it can be discharged to theenvironment without potential for harmful effects.Organohalogen. organophosphorus compounds and biocidesare among the priority substances listed for emission controlin the IPPC Directive. Worldwide, the most commonectoparasiticides used for treating sheep are diazinon (OP),propetamphos (OP). cypermethrin (SP) and cyromazine (fly-specific IGR), for control of blowfly. Insect growth regulatorssuch as dicyclanil, diflubenzuron and triflumuron areregistered only in Australia and New Zealand.Organochlorine pesticides (in particular,iii.•a~.•.lnln>~-Li~llil.<~ln.~ (iii. siin ruLilid oii woolcoining noiii inc ionnei Soviel utiion. lhe Middle East andsome South American countries [187, INTERLAfNE, 1999](see also Section the fate of ectoparasiticides when they enter thescouring process, a distinction has to be made betweenlipophilic and hydrophylic compounds such as cyromazine.The lipophilic compounds - OCs, OPs and SPs - associatestrongly with the wool grease and are removed with itduring scouring (although a fraction -up to 4 %-is retainedby the fibre and will be released in the subsequent finishingwet processes). This behaviour applies also to diflubenzuron(IGR). Recent studies have shown that triflumuron (IGR)associates partially with the dirt and partially with thegrease. As a result, compared to other lipophilic compounds,a higher proportion of this pesticide is likely to be retainedon-site (on the wool fibre and on the recovered wool greaseand dirt) and not be discharged in the aqueous effluent[103, G. Savage, 1998]. On the contrary. IGRs such ascyromazine and dicyclanil are appreciably water-soluble (I I
  8. 8. g/l at 20 °C, for cyromazine). which means that they are notremoved in wool grease recovery systems.In the waste water treatment systems an additional fractionof the pesticide residues is removed. Physico-chemicalseparation techniques remove the biocide residue atapproximately the same rate as the grease and the dirt withwhich they are associated. On the other hand, evaporationsystem removes Ocs and SPs in significant quantities. Butupto 30% of Ops may appear in the condensate becausethey are steam volatile. The water-soluble compounds, suchas the IGR cyromazine are probably not removed from theeffluent stream except by evaporating treatments [187.INTI-;RI.AINF.. 1999].Despite these treatments, the removal of pesticides is oftenincomplete and there is potential for pesticides to enter theaquatic environment when the effluent is discharged. Theenvironmental concentrations of ectoparasiticides in thereceiving water depend greatly on local circumstances, inparticular, the amount of scouring activity concentrated in agiven catchment and the dilution available between scouringdischarges and the river which receives the treated effluent.In areas of Europe with a high concentration of scouringactivity, there is a risk of high concentration levels ofpesticides in the receiving water. In this case, it is preferableto define discharge limits on the basis of risk assessmentmodels. In UK. for example, statutory environmental qualitystandards (EQS) for the OCs and non-statutory standards forthe OPs and cypermethrin have been defined. Dischargelimits are set up for processing mills by comparing the givenEQS targets with predicted environmental concentrationsbased on tonnage of wool processed and typical effluenttreatment systems.29. The control of the discharge limits at the scouring mills iscarried out by using data From the ENco Wool & HairPesticide database (to define the initial amount of residueson the incoming wool) in combination with the above-
  9. 9. mentioned water-grease partition factors for the differentpesticides. For more detailed information see also Sections2.1.1.9 and 32.1 ("Ectoparasiticides").Potential for pollution of landTwo main "wastes", grease and sludge, are produced as aconsequence of scouring activities (and related effluenttreatment). Depending on its oxidation extent, it may bepossible to recover from 20 to 40 % of the grease initiallypresent on the raw wool. This is to be regarded as a by-product rather than a waste, since it can be sold to lanolinrefiners for the production of high-value products in thecosmetic industry. However, high levels of pesticidesresidues in the grease can also be a problem for the lanolinrefiners, especially for the production of lanolin-basedpharmaceuticals and cosmetics. since more expensive andsophisticated techniques have to be used to reduce thepesticides to acceptable levels. Acid-cracked grease has nomarket value and has to be landfilled. The sludge producedas a result of physico-chemical treatment of waste wateralso contains grease, dirt and the portion of pesticides whichare strongly associated with either grease or dirt.Concentrates and sludges from evaporation or membranefiltration may also contain suint. which is mainly potassiumchloride and potassium salts of fatty acids. Suint is a by-product which can be used in agriculture.Sludge and concentrate disposal may follow several routes:• incineration (with heat recovery)Pyrolysis/gasifi cation• brick manufacturing• composting or co-composting with other organic material• landfill.The first three sludge disposal routes destroy the organicmaterial in the sludge, including grease and pesticides. Theash from incineration may contain potassium salts, derivedfrom suint, and heavy metals characteristic of the soil on
  10. 10. which the sheep producing the wool have grazed. The ash isnormally disposed of to landfill.The characteristics of the char from pyrolysis/gasification areunknown and this char is also typically disposed of tolandfill. The use of wool scour sludges in brick manufactureresults in no residues for immediate disposal.These three sludge disposal methods probably have theleast potential to pollute land.Wool scour sludges cannot be composted alone, but requirethe addition of carbon-rich organic material. Green wastefrom agriculture or horticulture has been used.Composting is not yet regarded as a fully developed, fail-safe technique and only partly degrades the pesticidespresent in the sludge. However, since the pesticides presentin the sludge are there because of their lipophilicity or theirstrong propensity to absorb onto solids, they are likely to beimmobile in soil. and spreading of compost derived fromwool scour sludges on agricultural land is unlikely to pose anenvironmental risk of any significance. Landfill is thesimplest and often cheapest method of disposal of sludges.In the longer term. however, landfill is not believed to beeither economically or environmentally sustainable. The fateof wool scour sludges in landfill is not known, but there is asmall potential for the cctoparasiticides present to arise inleachate. Anaerobic degradation of the organic material inthe sludge will give rise to methane emissions [187,INTERLAINE, 1999]. lexiiles Industry 2930 Potential for pollution of airAir pollution is not a main issue for wool scouring processes.Nevertheless two issues can be mentioned. Hot acidcracking, which involves heating the scour effluent withsulphuric acid, when used near residential areas, has beenthe subject of odour complaints. Incineration is used inconjunction with evaporation of the effluent because the
  11. 11. surplus heat from the incinerator can be used in theevaporation process. Incineration of wool scour sludges haspotential for air pollution. Since sludges contain relativelyhigh levels of chloride (from suint) as well as organicallybound chlorine from ectoparasiticides etc., there is potentialfor the production of polychlorodibenzodioxins and furans,when they are incinerated (catalytic and high temperatureincinerators are now available to prevent these emissions).The sludges also contain relatively high levels of sulphurand nitrogen and (the combustion process thereforeproduces SOx and N0x. Dust and odours should also betaken into account. Cleaning and washing with solvent2.3.1.4 Environmental issues associated with woolscouring (with organic solvent)The Wooltech system described above, usestrichloroethylene as solvent. Trichlorethylene is a non-biodegradable and persistent substance (trichloroethylene ison the EPER list). Unaccounted losses of this solvent arisingfrom spills, residues on the fibre, etc., if not adequatelytreated to destroy the solvent, may lead to diffuse emissionsresulting in serious problems of soil and groundwaterpollution. As far as water and energy consumptions areconcerned, the Wooltech system shows lower consumptionlevels compared to a typical scouring process using water. Amore accurate balance of the inputs and outputs in thisprocess is reported in Section Take from original text2.6.2 Wool preparation before colouringCarbinsingScouring, DrycleaningFullingBleaching
  12. 12. Environmental issuesWool pretreatment gives rise mainly to water emissions,although there are also specific operations (e.g. carbonisingwith the "Carbosol" system and dry cleaning) wherehalogenated organic solvents solvents can produce not onlyemissions to air, but also contamination of soil andgroundwater if their handling and storage is not done usingthe necessary precautions. Preventive and end-of- pipemeasures include closed-loop equipment and in-loopdestruction of the pollutants by means of advancedoxidation processes (e.g. Fenton reaction). See Sections4.4.4. 4.9.3 and 4.10.7 for more detailed information. Theprocess also involves the generation of exhausted activecarbon from the solvent recovery system. This solid wastehas to be handled separately from other waste material anddisposed of as hazardous waste or sent to specialisedcompanies for regeneration. Due to the predominantly batchnature of wool pretreatment operations for all types ofmake- ups, (the resulting emissions will be discontinuousand with concentration levels largely influenced by the liquorratios used. An exception is represented by carpet yarnwhich can be scoured/ bleached and mothproofed on tape or"package to package" scouring machines (see Section 2.14.5. 1 .2) giving rise to continuous flows.53 The pollutants that can be found in the waste water,originate in part from the impurities that are already presenton the fibre when it enters the process sequence and in partfrom the chemicals and auxiliaries used in the process.Pollution originating from impurities present on theraw materialResidues of pesticides used to prevent the sheep becominginfested with external parasites can still be found on scouredwool in amounts, which depend on the efficiency of the
  13. 13. scouring process. These are mainly organophosphates (OPs)and synthetic pyrethroid (SPs) insecticides and insect growthregulators (IGRs), but detectable residues of organochlorinepesticides (OCs) can be observed. They partition betweenthe fibre and the water according to their stronger or weakerlipophylic character and, as a consequence, traces of thesecompounds are released in the waste water. Moreinformation about ectoparasiticides can be found in Sections2.1.1.9 and The partition factors of the differentclasses of pesticides are discussed in more detail for thecarpet sector in Sections and Note thatbecause of their steam volatility some pesticides (OPs) endup in the air emissions from open machines. This must betaken into account in input/output balances. Spinninglubricants (see 8.2.3), knitting oils (see 8.2,5) and otherpreparation agents also represent an important issue in woolpretreatment. These substances are removed during thescouring process, contributing to the COD load and aquatictoxicity in the final effluent.The main concerns are about:• poorly refined mineral oils (content of aromatichydrocarbons)• APEO (non-biodegradable and giving rise to toxicmetabolites)• silicones (non-biodegradable and difficult to removewithout scouring assistants)• biocides (toxic to aquatic life).The dry spinning route in the carpet sector, described inSection represents one exception because in thiscase spinning lubricants do not reach the water effluent.Pollution originating from chemicals and auxiliariesused in the processConsiderable amounts of surfactants are used inpretreatment as detergents, wetting agents, etc.Surfactants with good biodegradability with acceptableperformance are now available (see Section 4.3.3).Nevertheless, the use of alkylphenol ethoxylates is still
  14. 14. common in some companies due to their low cost.Alkylphenol ethoxylates (APEOs) and in particularnonylphenol ethoxylates (NPEs) are under pressure due tothe reported negative effects of their metabolites on thereproduction system of aquatic species.The environmental issues arising from surfactants incommon use are discussed in Section 8.1.Other pollutants of concern that may be found in watereffluent from pretreatment activities are:• reducing agents from bleaching treatments and chemicalsetting of carpet wool yarn (sodium metabisulphite): theycontribute to oxygen demand in the waste water• poorly bio-eliminable complexing agents (e.g. EDTA, DTPA,phosphonates) from hydrogen peroxide stabilisers, etc.• AOX from sodium hypochlorite bleaching• insect-resist agents in wool carpet yarn production. Moredetails regarding environmental issues associated with theabove-mentioned substances are given elsewhere in thisdocument, in particular in Section and Section 8.5.