Characteristics of Effluent Water in Textile Wet Processing Industries | Classification of Textile Waste Which are Generated in Textile Industry

Characteristics of Effluent Water in Textile Industries:
ETP
As discussed textile sector is putting enormous impact on Bangladesh economy yet this industry is currently facing several challenges. Out of various activities in textile industry, chemical processing contributes about 70% of pollution. Waste stream generated in this industry is essentially based on water-based effluent generated in the various activities of wet processing of textiles. It is well known that wet processing mills consume large volume of water for various processes such as sizing, desizing, and scouring, bleaching, mercerization, dyeing, printing, finishing and ultimately washing. In fact, in a practical estimate, it has been found that 45% material in preparatory processing, 33% in dyeing and 22% are re-processed in finishing. But where is the real problem? The fact is that the effluent in textile generated in different steps is well beyond the standard and thus it is highly polluted and dangerous. This is demonstrated in Table 1.
Properties of Waste Water from Textile Chemical Processing:


Property
Standard
Cotton
Synthetic
Wool
pH
5.5 – 9.0
8-12
7-9
3-10
BOD, mg/l, 5 days
30-350
150-750
150-200
5000 – 8000
COD, mg/l, day
250
200-2400
400-650
10,000 – 20,000
TDS, mg/l
2100
2100-7700
1060-1080
10,000 –13,000

Classification of Textile Waste Which are Generated in Textile Industry:
Textile waste is broadly classified into four categories, each of having characteristics that demand different pollution prevention and treatment approaches. Such categories are discussed in the following sections:

A. Hard to Treat Wastes:
This category of waste includes those that are persistent, resist treatment, or interfere with the operation of waste treatment facilities. Non-biodegradable organic or inorganic materials are the chief sources of wastes, which contain colour, metals, phenols, certain surfactants, toxic organic compounds, pesticides and phosphates. The chief sources are:
  • Color & metal → dyeing operation
  • Phosphates → preparatory processes and dyeing
  • Non-biodegradable organic materials → surfactants
Since these types of textile wastes are difficult to treat, the identification and elimination of their sources are the best possible ways to tackle the problem. Some of the methods of prevention are chemical or process substitution, process control and optimization, recycle/reuse and better work practices.

B. Hazardous or Toxic Wastes:
These wastes are a subgroup of hard to treat wastes. But, owing to their substantial impact on the environment, they are treated as a separate class. In textiles, hazardous or toxic wastes include metals, chlorinated solvents, non-biodegradable or volatile organic materials. Some of these materials often are used for non-process applications such as machine cleaning.

C. High Volume Wastes:
Large volume of wastes is sometimes a problem for the textile processing units. Most common large volume wastes include:
  • High volume of waste water
  • Wash water from preparation and continuous dyeing processes and alkaline wastes from preparatory processes
  • Batch dye waste containing large amounts of salt, acid or alkali
These wastes sometimes can be reduced by recycle or reuse as well as by process and equipment modification.

D. Dispersible Wastes:
The following operations in textile industry generate highly dispersible waste:
  1. Waste stream from continuous operation (e.g. preparatory, dyeing, printing and finishing)
  2. Print paste (printing screen, squeeze and drum cleaning)
  3. Lint (preparatory, dyeing and washing operations)
  4. Foam from coating operations
  5. Solvents from machine cleaning
  6. Still bottoms from solvent recovery (dry cleaning operation)
  7. Batch dumps of unused processing (finishing mixes)

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