Pollution Prevention Tips for Wet-Processing Textile Mills
A Publication of the Georgia Pollution Prevention Assistance Division
The largest waste stream from most textile mills involved in washing, bleaching, and dyeing is wastewater. Textile mill wastewater is often contaminated with process chemicals (dye, salt, bleach, detergent, etc.), oil, and energy from hot water discharges. As a result, wastewater discharge permit limits, such as BOD (biological oxygen demand), COD (chemical oxygen demand), aquatic toxicity, and metals content, are often difficult to meet. Water usage in a typical mill can easily top 40,000 gallons per day costing more than $30,000 annually in water and sewer fees. Here are some ways to reduce water use, pollution, and cost.
Spills and cleanup can be a major source of water pollution. Process chemicals are stored, mixed, transported, and spilled in most mills. Seemingly minor spills can have major impacts on wastewater. A spill of 5 pounds of salt will contaminate 2,700 gallons of water. If a 50-pound bag of salt bursts in handling, 27,000 gallons of water would be contaminated. The best solution is to avoid the spill. The next best solution is to sweep up the spill and reuse the salt. If the floor is reasonably dry when the spill first happened, dry cleanup and reuse is usually easy to achieve. If a liquid product is spilled, dry cleanup, using absorbent clay and sweeping, is a better solution than washing it down the floor drain.
Another area where waste can be reduced is in chemical mixing. Adding excessive chemicals to recipes will increase cost and may cause quality problems. Different dye mixtures will require varying amounts of salt to achieve complete exhaustion. Adding too much salt may cause few quality problems, but will result in increased salt in the wastewater discharge. Adding too little salt will reduce the amount of dye fixing to the cloth; this will result in an overuse of dye, dye in the wastewater, and quality problems. Following specific recipes each time can avoid problems such as these. All parameters, including the temperature and amount of water added to a bath, should be documented and provided to mill operators responsible for mixing chemistry. Measuring equipment, such as scales and measuring cups, must also be provided to avoid "eyeball" measurements and errors.
Water usage can be reduced in mills by making simple housekeeping changes in addition to process modifications. It is very common for garden hoses to be left running continuously in textile mills. Usually a hose is allowed to discharge into a floor drain between uses rather than being turned off because the hose end may be 50 feet from the valve. A single hose left running will waste 7,200 gallons daily and cost more than $5,000 annually in increased water usage. A very simple solution is to attach a spring loaded nozzle, costing less than $5, to the hose. The operator is happier, and water usage is reduced. Leaks are another major problem in mills. Heavy use of salt, acid, and caustic results in valve and piping failure. Replacing steel valves and piping with plastic is a low-cost way to reduce leaks.
Process changes can make substantial reductions in water and energy use. Water flow through a rinsing process can be reduced by 50% if counter current or two-stage rinsing is used. Counter current rinsing is a process where the "dirtiest" fabric contacts the "dirtiest" water first; clean water rinses the fabric as it leaves the process. Continuous rinsing processes are usually designed with counter current rinsing. Batch processes can be modified to use two-stage or multi-stage rinsing; water used for rinsing the previous bath is used to provide initial rinsing of the next batch. This water is then discharged and clean water is used to provide final rinsing. A two-stageprocess like this one may replace threeseparate rinsing cycles using clean water toachieve the same level of cleanliness.
There are many opportunities to reuse wastewater in a textile mill. For example, final rinse water from dyeing can be used as make-up water for the dye bath. Final rinses from scouring and bleaching may be used for makeup water in desizing. Wastewater from many sources may be suitable for washing process equipment and floors (after sweeping or other dry cleanup). Some mills have reduced operating costs substantially by installing water reuse systems.
Pollution Prevention Check List for Textile Mills
· Store dry materials, such as bags of salt or dye drums, off of the floor and away from liquids by placing catch pans beneath the material.
· Plug floor drains in material storage areas.
· Build curbs around storage areas to keep spills in and water out.
· Remove water supplies from storage areas.
· Use dry cleanup methods; provide brooms, vacuums, and absorbent.
· Provide suitable work areas, handling tools, and training to operators so they can avoid creating spills.
· Provide recipes for each chemistry.
· Provide measuring equipment, in addition to recipes, to operators.
· Optimize chemistry; correct temperature can reduce the use of salt and dye.
· One size does not fit all; use small volume equipment for small production runs.
· Place spring loaded nozzles or timers on all water supplies to turn off when not used.
· Select valve and piping material to minimize corrosion and leaks.
· Avoid filling process equipment with water from unmetered hoses; place meters on water supplies feeding process equipment.
· Use counter current or multi-stage rinsing to reduce water use.
· Test incoming water supply for minerals or chemicals that negatively affect the process.
The Pollution Prevention Assistance Division (P2AD) is available to help Georgia companies reduce waste and increase profits through pollution prevention. Services range from telephone assistance to on-site evaluations and consultations. The service is free, confidential, and non-regulatory. For more information call Jancie Hatcher at 404.651.5120, 800.685.2443 in Georgia, or e-mail at email@example.com.