Section 4.    TEXTILE WASTES
CASE HISTORY:
PRETREATMENT OF TEXTILE WASTEWATER
Randy Junkins, Manager
Operation and Maintenance Section
Weston Designers-Consultants
West Chester, Pennsylvania 19380
The finished products of the textiles industry are manufactured from wool, cotton,
synthetic fibers or combinations thereof. The processing which the raw fibers undergo are
aimed toward: (1) removal of natural impurities; and (2) providing desired qualities of sight,
touch and durability.
The degree to which these objectives are pursued determines the characteristics of the
wastewater generated by a textile mill. For example, the amount of organic matter that is
removed from a fabric in the course of normal textile processing can be visualized when one
considers that about 10% of the gross weight of a cotton fabric consists of natural impurities
which may be removed in processing. For a firm that manufactures 20 tons of fabric per
week, a common production level, this means that 2 tons per week of impurities are discharged to the sewer and must be removed from the plant effluent. This chapter presents
a case study concerning the treatment of textile industry wastewaters. Production processes,
wastewater sources and characteristics and wastewater management strategies are discussed.
Textile mill operations consist of various processes such as weaving, dyeing, printing and
finishing. These processes can involve several steps, e.g., sizing, kiering, desizing, bleaching
and mercerizing, each contributing a particular type of waste. The sources of polluting compounds are the natural impurities extracted from the fiber, and the processing chemicals
which are removed from the cloth and discharged as waste.
In bleaching and dyeing textile materials, some continuous processes are utilized, but
many batch unit operations, such as kier boiling and dyeing operations, are also used. These
batch processes produce sudden changes in wastewater composition. The type of fiber
being processed also affects the composition of the waste; cotton and linen contribute organic matter from the noncellulosic materials that are present in the natural fibers, while
wool contains sand, grease and suint which are removed during scouring. Synthetic fibers
may contain spinning oils and anti-static dressings. The composition of a plant's effluent will
therefore vary with the fibers that are being processed. Variability in composition is a
marked feature of most textile works effluents, and wide variations in composition, temperature, flow and pH values are prevalent. Textile wastes are generally colored, highly alkaline,
and high in BOD, suspended solids and temperature.
Equalization is generally a preliminary treatment step for textile wastes due to their
variable composition. Chemical coagulation and biological treatment are the treatment
methods most often used for removal of color and dissolved organics [e.g., biochemical oxygen demand (BOD)]. Alum, ferrous sulfate, ferric sulfate and ferric chloride are used as
coagulants, in conjunction with lime and sulfuric acid for pH control. Calcium chloride has
also been found effective in such procedures as coagulating wool-scouring wastes. Biological treatment via the activated sludge process or trickling filters is frequently used successfully to remove soluble organics.
In-plant measures that can be implemented to reduce the quantity and strength of textile
wastes include: (1) good housekeeping; (2) process control; (3) process chemical substitution; and (4) chemical recovery.
Close control of kiering, sizing and chemical usage may reduce pollutant loads by 30%.
Chemical substitution (e.g., use of ammonium sulfate instead of acetic acid for scouring) can
also be an effective method to reduce in-plant BOD loads.
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