During the last 50-75 years, there has been ever-increasing efforts to somehow arrange manufacturing processes in such a way that they cause minimal damage to the environment. Efforts focused on the technology of waste treatment development at the same time, and an uneasy adversarial relationship developed between regulators and industry. Waste minimisation is the application of a systematic approach to reducing the generation of waste at source. In other words, waste minimization prevents the waste from occurring in the first place, rather than treating it once it has been produced by end-of-pipe treatment methods.
Waste minimization applies to hazardous materials, non-hazardous materials, water, energy, raw materials, all waste emissions, and other resources. It is NOT a one-off activity, but an ON-GOING programmer. That is, it is a technique that can be applied to all inputs to and outputs from, a process. Waste minimization is important because it reduces operating costs, risk of liability and end-of-pipe treatment, improves process efficiency, enhances public image, protects health and environment, and improves employee moral. Waste is not only materials that are excess to requirements, but represents a loss of company profits.
There is an attempt to review the various waste minimisation techniques and possibilities that are available for the textile industry today.
Source reduction :
Waste minimisation is achieved through source reduction by making process and product changes. Product changes include increasing product life, and designing for less environmental impact. Process changes include improved operating practices, improved housekeeping, change in raw materials, change in technology, in-house reuse or recycling. End-of-pipe treatment is only considered after source reduction.
Four main types of wastes are particularly amenable to source reduction:
(1) Hard to treat,
(2) Dispersible,
(3) Offensive and
(4) High volume.
Reducing water consumption:
Water consumption in a textile factory can be reduced by implementing various changes ranging from simple procedures such as fixing leaks, to more complex options such as optimising water use and reducing the number of process steps. They include:
# Repairing leaks, faulty valves, etc: A simple method of determining if leaks exist is to take incoming water metre readings before and after a shut-down period when no water is being used. A difference in the readings could indicate a leak.
# Turn off running taps and hoses: Encourage workers to turn off taps and hoses when water is not required. The fixing of hand triggers to hoses also reduces water consumption.
# Turn off water when machines are not running: Encourage workers to turn off machines and water during breaks and at the end of the day. Avoid circulating cooling water when machines are not in use.
# Reduce the Number of Process Steps: This involves a study of all the processes and determining where changes can be made. For example, fewer rinsing steps may be required if a dye with high exhaustion is used.
# Optimise process water use: Examples include using batch or stepwise rinsing rather than overflow rinsing, introducing counter-current washing in continuous ranges, and installing automatic shut-off valves.
# Recycle cooling water: Cooling water is relatively uncontaminated and can be reused as make-up or rinse water. This will also save energy as this water will not require as much heating.
# Re-use process water: This requires a study of the various processes and determining where water of lower quality can be used. For example, final rinse water from one process can be used for the first rinse of another process.
# Using water efficient processes and equipment: Although replacing outdated equipment with modern machines which operate at lower liquor ratios and are more water efficient requires capital investment, the savings that can be made ensure a relatively short pay-back period.
# Sweeping floors: Instead of washing the floors of the dye house and kitchens, rather sweep up any spillages 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 as solids.
# Reusing water from auxiliary processes: The water used in the rinsing of ion-exchange columns and sand filters can be reused elsewhere in the factory.
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 effluent strength and therefore lower treatment costs, as well as overall savings in chemical costs. Various options for reducing chemical use are listed below:
# Recipe optimisation: Recipes 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 use and lower costs. Continual updating of recipes should be carried out when new dyestuffs enter the market as, in general, less of these chemicals are required.
# Dosing control: Overdosing and spillages can be reduced by mixing chemicals centrally and pumping them to the machines. Check that manual measuring and mixing is carried out efficiently and automatic dispensers are properly calibrated.
# Pre-screen chemicals and raw materials: Avoid dyestuffs containing heavy metals, solvent-based products and carriers containing chlorinated aromatics. Safety data sheets should be obtained from the chemical manufactures to obtain information such as toxicity, BOD and COD. Check that raw materials do not contain toxic substances. Check that companies will accept expired raw materials for disposal.
# Chemical substitution: Review chemicals used in the factory and replace those hazardous to the environment with those that have less of an impact. Use dyes that have high exhaustion rates and require less salt. Specifically replace metal-containing dyes, use bi-reactive dyes in place of mono-reactive, avoid the use of APEO detergents and replace with more biodegradable alternatives, replace stilbene optical brighteners with alternatives, or eliminate altogether, dye wool with dyes that do not require after-chroming.
# Correct storage and handling: More effective control of the storage and handling of chemicals will results in less spillage reaching the drains.
# Chemical recovery and reuse: Chemical use may be reduced through recovery and reuse. For example, sodium hydroxide from mercerising can be recovered through evaporation. Dye baths may be reused and size can be recovered for reuse.
# Process changes: Investigate the feasibility of changing to cold-pad batch dyeing. This results in less chemicals being used (and in particular, salt) and reduces water consumption significantly.
# Improve scheduling: Review the scheduling of continuous processes such as sizing, desizing, padding etc. to ensure that the same chemical bath is used as many times as possible, thus reducing the number of dumps to drain per day.
Energy conservation:
As with water conservation, reductions in energy use can result in substantial savings and lower emissions from boilers or generating plants. They include optimising compressed air generation, installing compressor control systems, and general housekeeping
Reduce cooling loads, decrease condensing temperature (as a guideline, reducing condensing temperature by 1oC will yield savings of between 2% and 4% of annual refrigeration cost); Increase evaporating temperature (as a guideline, increasing evaporator temperature by 1oC will yield savings of between 2% and 4% of annual refrigeration cost); Compressor control, incorrect control of compressors can increase costs by 20%, or more; Boiler blowdown, economisers, insulation, flash steam recovery, good housekeeping, installing heat exchangers, optimising plant environmental conditions, shutting off of lighting, air-conditioning, etc.
Reducing solid waste:
In terms of volume, solid waste is the second largest waste stream in the textile industry next to liquid effluent. There are a number of waste minimisation options available to reduce solid waste, and these include:
i) Reducing the amount of packaging material by improved purchasing practices such as ordering raw materials in bulk or returnable intermediate bulk containers (IBCs). This reduces spillages, handling costs, exposure of workers to chemicals and the amount of storage space required. ii)Purchasing chemicals in returnable drums. Enquire if vendors will accept unwashed drums as this will reduce the waste water generated in the factory. If possible, ordering chemicals in IBCs rather than bags as these are easily broken, causing spillages.
iii) Purchasing yarn on reusable plastic cones rather than cardboard cones.
iv) Reducing seam waste through effective training programmes.
v) Selling waste fibres, sweeps, rags, yarn and cloth scraps.
