Process Flow of Effluent Treatment in a Textile Industry
Typically the following process flow of effluent treatment is followed in a typical textile industry;
The purpose of screening is to filter out the loose impurities. Thus wood, paper plastic bags etc. can be removed by this method. A method of progressive filtering is followed where first the matter is passed through coarse screens and then through fine screens.
Oil and Grease Removal
Many units discharge water mixed with oil. The purpose of this equipment is to remove the oil. Since surface density of oil and grease is less than water, the oily substance come on the surface of the water and can be skimmed.
The effluent from the primary treatment is cooled ( cooling towers are employed for this purpose) and then uniformly mixed using equlisation tank. It takes in any sudden gush of effluents as well as slow rate of effluent and feeds to the subsequent processes in a uniform way.
pH Adjustment ( Acid or Alkaline Dosing)
The waste from the Textile Industry is rarely pH neutral. To increase the efficiency of biological treatment and coagulation/flocuculation a pH of 6-8 is needed. Generally Sodium hydroxide is used to neutralise acidic waste and hydrochloric acide is used to neutralize alkaline waste. Generally the effluents from the dyeing industry have high pH and hence an acid addition is required.
It is reuqired to control BOD. Two main methods are used: one in which water is mechanically agitated so that air from atomoshphere may enter into the water, second method is introducing the air in the water through blowers and using diffusers to diffuse the air uniformly.
Generally organic matter present in the effluent takes oxygen from the water, which increases its oxygen demand, to avoid that chlorine is added to oxidise the matter.
The purpose of clarification is to remove any suspended solids by coagulation and flocculation. It is done using flash mixer. In flash mixer, alum solution is dosed as coagulant.
The flocculated water flows upwards towards tube settler. The suspended solids settle down.
This settling can also be done using lamella filter
It achieves solid liquid separation by directing the liquid between a seris of inclined plates called lamellae. It settles suspnded solids by gravity.
To be continued
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