2. Introduction
In textile mills mainly, the waste water discharge is the effluent which contains :
• Organic matter
• Inorganic matter
• Dissolved solids
• Suspended solids
• Dyes
• Chemicals & Auxiliaries
• Metal Toxicants
They directly or indirectly shows effect in the color, alkalinity, pH, hardness, BOD, COD
values of water.
• Primary goal is to reduce the effect on ENVIRONMENT -- by determining the type
of pollutants.
3. -- and giving treatment accordingly.
Need of Effluent Treatment Study
Raw Effect Samples Treated Effluent Samples
4.
5.
6.
7. Classification of textile wastes
• Hard to treat
- Colours, Metals, Phenol
• Toxic organic compounds
• Phosphates
• Non-biodegradable surfactants
• Hazardous or toxic
• Dispersible
Stages of Effluent treatment process
8. • Primary
Removes identifiable suspended solids and floating materials.
• Secondary
▫ Also known as biological treatment.
▫ Removes organic matter that is in soluble form or colloidal form.
• Tertiary
▫ Removes sodium and chlorides ions.
▫ Removes additional suspended solids including algae, fungal bacteria, etc.
11. Screening
Coarse suspended matters such as rags, pieces of fabric, fibres, yarns and lint are removed.
Bar screens and mechanically cleaned fine screens remove most of the fibres.
Sedimentation
• This process is particularly useful for treatment of wastes containing high percentage of
settable solids or when the waste is subjected to combined treatment with sewage.
• The sedimentation tanks are designed to enable smaller and lighter particles to settle under
gravity.
Equalization
These effluent streams are segregated and stored in separate tanks, and this liquid
effluent may be dosed at regular and uniform rate which is known as equalization.
This process is carried out to equalize the pH.
13. • Mercerizing discharges are highly alkaline liquors, and carbonizing discharges are
highly acidic nature. Diluted by adding of H2SO4 or CO2 or flue gas.
Chemical Coagulation
• To remove colour, suspended solids, colloidal particles, the effluents are treated with
coagulants like Alum, Ferrous Sulphate, Ferric Chloride, Sodium Aluminate and
activated Silica in a clariflocculator
• Acids such as polyelectrolytes are used along with coagulants to improve coagulation.
Sludge is separated and dried on sand beds. Treated effluent is subjected to secondary
treatment.
16. Aerated lagoons (tanks)
• Large cement tanks having 3-5 m depth. Effluent from Primary Treatment are stored in
these tanks for 2-6 days which are aerated mechanically.
• After 2-6 days of aeration, a healthy flocculent sludge forms, which carry out oxidation
of organic matter. It removes 90% of BOD.
Trickling filtration
• Effective aerobic biological oxidation method widely used. The effluent is sprinkled over
a bed of broken stones. Bacterial slimes formed on the stones oxidizes Organic matter
during the passage. Effluent is finally settled and discharged.
Activated Sludge Process
• Here the effluent is continuously exposed and subjected to biological degradation
carried out by ‘Microbial Floc’ suspended in reaction tank into which oxygen is
17. introduced by mechanical means. The effluent from this tank is allowed to settle and
a portion is recycled.
Comparison of trickling filters with activated sludge systems
Trickling Filters Activated sludge systems
Bacterial growth is fixed on the media. Bacterial growth is suspended as a dispersed floc.
All solids from the settler are wasted. Solids from the settler are partially recycled.
Less sensitive to shock loading - more
stable.
More sensitive to shock loadings, require closer
process control.
Produce insects and odors Produce spray clouds.
Less effective in removing disease causing
organisms.
More effective in removing pathogens than
trickling filters.
Low operating costs. High operating costs.
18. Oxidation ponds
• An oxidation pond is a large shallow pond. Stabilization of organic matter is brought out
by bacteria. Oxygen is required for this purpose of metabolism and is supplied by algae.
The algae utilizes the carbon dioxide released by bacteria for photosynthesis.
• For effective treatment : 1)Maximum sunlight penetration (for photosynthesis), 2) Wind
action for mixing , 3) Neutral Aeration
Sludge treatment & disposal
• The Concentration of solids in the primary sewage sludge is about 5%, Activated sludge
contains less than 1 % solids and the sludge from trickling filters contain 2% solids.
• In addition to reducing water content sludge must be stabilised, conditioned to reduce
biological activity disinfected before disposal.
Sequence of Operation for Sludge Treatment
21. Evaporation
• It is a simple process of boiling the waste and vaporizing the waste water. This process is useful
only when the recovered water and solids are re-used and recycled.
• Various fuel systems like coal, wood, use of stem are employed for evaporating these effluents.
Dialysis
• This is a method of separating solutes from the solution based on the difference in the rates of
diffusion.
• This process is mainly used for recovering NaOH from mercerizing and H2SO4 from carbonizing.
Chemical precipitation
• If the dissolved solids in the effluent can be precipated, they can be easily removed.
• Lime is the effective and cheapest precipating agent.
• Proteins are precipated using sulphuric acid.
22. Ion exchange
• Ion exchange method is extensively used to remove hardness, iron and magnesium
salts.
Removal by algae Reverse osmosis
• This process is much similar to oxidation ponds. Algae requires Potassium,
Calcium and magnesium. Traces of Manganese cobalt and Copper are required.
23.
24. Carding Combing
Drawing
Spinning Sizing Weaving
Effluent
Raw Cotton
Grey cloth
Desizing
Scouring
Bleaching
Dyeing
Finishing
Mercerizing
Printing
Effluent
Effluent
Effluent
Effluent
Effluent
Effluent
The Processes carried out in a textile mill
25. Dyes in wastewater
• Reduces the depth of penetration of sunlight - decreases photosynthetic activity and
dissolved oxygen.
• dyeing cotton with reactive dyes are highly polluted and have high BOD/COD, coloration,
and salt load.
• Marrot and Roche Review :
1)Physical methods include precipitation (coagulation, flocculation, sedimentation)
2) Adsorption (on activated carbon, biological sludges)
3) Filtration (Micro filtration, Nano filtration)
4) Membrane processes (osmosis and reverse osmosis)
26. from the textile effluent
Electrochemical treatment and recovery of chemicals
A flow diagram for treatment of cotton
textile mill waste
29. • Biological treatments: Self-purification that exists in nature. Most of dyes resist aerobic
biological treatment. BAF-based technologies have been developed to treat wastewater.
• Coagulation–flocculation treatments: Used to eliminate organic substances.
• Adsorption on powdered activated carbon: Reduction of suspended solids and organic
substances, as well as a slight reduction in the color.
• Electrochemical processes: The removal of dyes from aqueous solutions results from
adsorption and degradation of the dye-stuff. sludge formation is absent in this
method.
1) Electrolytic reactions at the electrodes
2) Formation of coagulants in the aqueous phase
3) Removal by sedimentation and floatation
Under optimal conditions, decolorization yields between 90 and 95%, and
COD removal between 30 and 36% can be achieved
30. • Ozone treatment: Ozone especially attacks the double bonds. It does not lead to a
significant reduction in COD
• Azo dyes precursors and degradation products (such as aromatic amines) are highly
carcinogenic.
• Removal of dyes from wastewater can be effected by chemical coagulation, air flotation,
and adsorption methods.
• advance oxidation is a potential alternative to degrade azo dyes into harmless species.
31. Membrane processes
Recommendations for effluent management in textile industries
• The multiple effect evaporation with crystallizer has been installed for recovery glauber salt.
• Reverse osmosis membrane filtration can produce colourless treated effluent with dissolved
solids as low as 196 mg/l and zero hardness.
32. • Recycling and reuse of the treated effluent directly conserve natural resources and a step towards
sustainable development.
• Low polluting stream contains nominal dissolved solids so that it meets quality requirement for
its reuse or disposal after treatment.
• For effective effluent management as follows:
1) The highly polluting effluent stream can be segregated and treated separately. This stream
has low volume and as such, it can be disposed of through solar evaporation pond where
adequate land is available.
2) The other low polluting streams can be given primary/secondary/tertiary treatment to
meet the disposal standards or for use in industry for appropriate operations.
3) Dye bath effluent is to be treated using a nano filtration system and wash water can be
treated separately in primary/secondary/tertiary treatment to meet the disposal standards or
for reuse. It can also be treated with reverse osmosis system to recover and recycle water.
33. 4) The effluent stream arising out of textile processing can be collectively treated using
primary/secondary/tertiary treatment to meet the disposal standards. In case water is intended
to be reused, the treated water can be further purified with use of reverse osmosis or other
methods.
5) The reject stream of reverse osmosis can be disposed of through solar evaporation ponds
or other evaporation system.
References
• Cotton Textile Processing: Waste Generation and Effluent Treatment The
Journal of Cotton Science 11:141–153 (2007)
• Advanced Methods for Treatment of Textile Industry Effluents
Resource recycling series RERES /7/2007
