Role of Textile Effluent Treatment Plants (ETP) to Control Environmental Pollution
Various aspects of ET Plants (ETP) and a real-time industry case study
Effluents Treatment Plants or ET Plants (ETP) are the most widely accepted approaches towards achieving environmental safety. But, no single treatment methodology is suitable or universally adaptable for any kind of effluent treatment.
Categorization of Waste 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:
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 color, metals, phenols, certain surfactants, toxic organic compounds, pesticides, and phosphates. The chief sources are:
- Colour & metal à dyeing operation
- Phosphates à preparatory processes and dying
- Non-biodegradable organic materials à 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.
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.
High Volume Wastes
A large volume of wastes is sometimes a problem for the textile processing units. Most common large volume wastes include:
- The high volume of wastewater
- 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 recycling or reuse as well as by process and equipment modification.
The following operations in textile industry generate highly dispersible waste:
- The waste stream from continuous operation (e.g. preparatory, dyeing, printing and finishing)
- Print paste (printing screen, squeeze, and drum cleaning)
- Lint (preparatory, dyeing and washing operations)
- Foam from coating operations
- Solvents from machine cleaning
- Still bottoms from solvent recovery (dry cleaning operation)
- Batch dumps of unused processing (finishing mixes)
Search for Solution
Each type of waste/waste stream represents an individual problem which can be solved only by taking into consideration the following factors:
- Local conditions
- Dyestuff and chemical used
- Amount and composition of the wastewater
- Local drainage conditions
- Main sewage channel
- Sewage characteristics etc.
Our aim is to adopt technologies giving minimum or zero environmental pollution. Effluents treatment plants are the most widely accepted approaches to achieving environmental safety. But, unfortunately, no single treatment methodology is suitable or universally adaptable for any kind of effluent treatment. For instance, in the past, biological treatment systems had been used extensively but they are not efficient for the color removal of the more resistant dyes .
Therefore, the treatment of waste stream is done by various methods, which include physical, chemical and biological treatment depending on pollution load. The treatment processes may be categorized into the preliminary, primary, secondary and tertiary treatment process. Various operations in each category are described below in Table 2.
|Mechanical flocculation & Chemical coagulation
|Activated sludge process
|Oxidation ditch & pond
|Electrolytic precipitation & Foam fractionation
|Ion exchange method
|Adsorption (Activated Carbon etc.)
|Table 2. Classification of the wastewater treatment process