Waste minimisation guide_for_the_textile_industry_a_step_towards

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  • Waste Minimisation Guide for theTextile Industry

    A Step Towards Cleaner Production

    Volume IAppendices

    Appendix 1: Waste Minimisation Options for the Textile IndustryAppendix 2: Case StudiesAppendix 3: Typical Pollution Loads from the Textile IndustryAppendix 4: End-of-pipe Treatment MethodsAppendix 5: References, Bibliography and Recommended ReadingsAppendix 6: Supporting DataAppendix 7: Useful OrganisationsAppendix 8: Sample Presentation

    by Susan Barclay and Chris Buckley

    The Pollution Research Group

    University of NatalDurban

    South Africa

    For The South African Water Research Commission

  • Appendix 1

    Waste Minimisation Options for the Textile Industry

    This Appendix contains detailed descriptions of the various waste minimisationoptions that are available for the textile industry. They are divided into 2 mainsections:

    w General waste minimisation suggestions for reducing water, chemical andenergy consumption; reducing solid waste; reducing air and noise pollution; andminimising the emission of toxic substances.

    w Specific waste minimisation suggestions for each textile process.

    A more detailed description of these options can be found in the literature and it issuggested that you refer to the following books / reports :

    w Best Management Practises for Pollution Prevention in the Textile Industry,United States Environmental Protection Agency (1996);

    w Water and Chemical Use in the Textile Dyeing and Finishing Industry,Environmental Technology Best Practice Programme (1997);

    w The Textile Industry and the Environment, United Nations EnvironmentProgramme (UNEP) (1994);

    w Cleaner Technology Transfer to the Polish Textile Industry - Idea Catalogueand Selected Options, Danish Environmental Protection Agency (1997).

    A1.1 Reducing Water Consumption

    Water consumption in a textile factory can be reduced by implementing variouschanges ranging from simple procedures such as fixing leaks, to more complexoptions such as optimising water use and reducing the number of process steps.Some suggestions are outlined in this section.

    A1.1.1 Repair Leaks, Faulty Valves, etc. A simple method of determining if leaks exist is to take incoming water meterreadings before and after a shut-down period when no water is being used. Adifference in the readings could indicate a leak.

    A1.1.2 Turn off Running Taps and HosesEncourage workers to turn off taps and hoses when water is not required. The fixingof hand triggers to hoses also reduces water consumption.

    A1.1.3 Turn off Water when Machines are not Running. Encourage workers to turn off machines and water during breaks and at the end ofthe day. Avoid circulating cooling water when machines are not in use.

    A1.1.4 Reduce the Number of Process Steps.This involves a study of all the processes and determining where changes can bemade. For example, fewer rinsing steps may be required if a dye with highexhaustion is used.

    A1.1.5 Optimise Process Water Use.Examples include using batch or stepwise rinsing rather than overflow rinsing,introducing counter-current washing in continuous ranges, and installing automaticshut-off valves.

    A1.1.6 Recycle Cooling WaterCooling water is relatively uncontaminated and can be reused as make-up or rinsewater. This will also save energy as this water will not require as much heating.

    Waste Minimisation Guide for the Textile Industry : A Step Towards Cleaner Production (Volume 1) January 2000

  • A1.1.7 Re-use Process Water This requires a study of the various processes and determining where water of lowerquality can be used. For example, final rinse water from one process can be used forthe first rinse of another process.

    A1.1.8 Using Water Efficient Processes and Equipment Although replacing outdated equipment with modern machines which operate atlower liquor ratios and are more water efficient requires capital investment, thesavings that can be made ensure a relatively short pay-back period.

    A1.1.9 Sweeping FloorsInstead of washing the floors of the dyehouse and kitchens, rather sweep up anyspillages and wash down only when essential. Not only will this reduce water use,but also the concentration of contaminants to drain as the waste is disposed of assolids.

    A1.1.10 Reusing Water from Auxiliary ProcessesThe water used in the rinsing of ion-exchange columns and sand filters can bereused elsewhere in the factory.

    A1.2 Reducing Chemical Consumption

    The majority of chemicals applied to the fabric are washed off and sent to drain.Therefore, reducing chemical consumption can lead to a reduction in effluentstrength and therefore lower treatment costs, as well as overall savings in chemicalcosts. Various options for reducing chemical use are listed below :

    A1.2.1 Recipe OptimisationRecipes are generally fail-safe designed which results in the over-use of chemicals.Optimising the quantity of chemicals required will lead to more efficient chemical useand lower costs. Continual updating of recipes should be carried out when newdyestuffs enter the market as, in general, less of these chemicals are required.

    A1.2.2 Dosing ControlOverdosing and spillages can be reduced by mixing chemicals centrally andpumping them to the machines. Check that manual measuring and mixing is carriedout efficiently and automatic dispensers are properly calibrated.

    A1.2.3 Pre-screen Chemicals and Raw MaterialsAvoid dyestuffs containing heavy metals, solvent-based products and carrierscontaining chlorinated aromatics. Safety data sheets should be obtained from thechemical manufactures to obtain information such as toxicity, BOD and COD.Check that raw materials do not contain toxic substances. Check that companieswill accept expired raw materials for disposal.

    A1.2.4 Chemical SubstitutionReview chemicals used in the factory and replace those hazardous to theenvironment with those that have less of an impact. Use dyes that have highexhaustion rates and require less salt.Specifically :

    w replace metal-containing dyesw use bi-reactive dyes in place of mono-reactivew avoid the use of APEO detergents and replace with more biodegradable

    alternativesw replace stilbene optical brightners with alternatives, or eliminate alltogetherw dye wool with dyes that do not require after-chroming

    A1.2.5 Correct Storage and HandlingMore effective control of the storage and handling of chemicals will results in lessspillages reaching the drains.

    Appendix 1-2

    Waste Minimisation Guide for the Textile Industry : A Step Towards Cleaner Production (Volume 1) January 2000

  • A1.2.6 Chemical Recovery and ReuseChemical use may be reduced through recovery and reuse. For example, sodiumhydroxide from mercerising can be recovered through evaporation. Dye baths may bereused and size can be recovered for reuse.

    A1.2.7 Process ChangesInvestigate the feasibility of changing to cold-pad batch dyeing. This results in lesschemicals being used (and in particular, salt) and reduces water consumptionsignificantly.

    A1.2.8 Improve SchedulingReview the scheduling of continuous processes such as sizing, desizing, paddingetc. to ensure that the same chemical bath is used as many times as possible, thusreducing the number of dumps to drain per day.

    A1.3 Energy conservation

    As with water conservation, reductions in energy use can result in substantialsavings and lower emissions from boilers or generating plants. Some energy efficientoptions are listed below.

    A1.3.1 Compressed Air

    Optimise compressed air generationTo keep generation costs to a minimum:

    w pressure control should be based on the pressure at the most sensitive / criticalpieces of machinery;

    w compressor sequencing should be based on a narrow pressure band in order toachieve the minimum generation pressure at all times. Care should be taken,however to avoid excessive cycling.

    Reducing generation pressure by 10% will yield savings of 5% of annual compressoroperating cost.

    Fix compressed air leaksNo-load tests should be carried out regularly, approximately every 2 to 3 months.All air leaks should be tagged and repaired at the earliest opportunity. Ultrasonicdetection devices are available to assist in leak detection.

    Optimise compressor sizingCompressors should be sized as closely as possible to the duty. It is noteconomical to run any machine for long periods at low loads; the off-load powerconsumption can be between 15% to 70% of on-load power once motorinefficiencies have been taken into account. In general, reciprocating compressorsoffer the highest part-load operating efficiently, if it is well maintained

    Install compressor control systemsFor multiple compressor installations, a modern compressor control system cansave between 5% and 20% of total generation costs for a modest capital outlay.Many modern controllers comprise cascade control, run-on timers and pressurecontrol. The latter is important in installations where the demand for air fluctuatessignificantly. It enables a lower generation pressure at times when air demand (andtherefore system pressure drops) is reduced.

    General housekeepingThe following general items should be considered when addressing compressed airefficiency:

    w Ensure that the air fed to compressors is as cool as practicable. A 4oC drop ininlet temperature will give savings of 1% of generation efficiency. Air-cooled

    Appendix 1-3

    Waste Minimisation Guide for the Textile Industry : A Step Towards Cleaner Production (Volume 1) January 2000

  • compressors should be fitted with ductwork to atmosphere, such that the exitingwarm air does not overheat the plantroom.

    w Ensure that air dryers are installed downstream of the air receiver. The receiveracts as a pre-dr