Waste water treatment

WASTE WATER TREATMENT AND
DISPOSAL OF TEXTILE EFFLUENTS
By - Iti dubey

Effluent:
• Effluent is liquid discharged from any source. Effluent can originate from
municipalities industries, farms ,ships, parking lots and camp ground.
There is a connotation that effluent contains contaminants but in the
strictest sense ,it could be pure water.
• The term effluent refers to the left over dyes and auxiliaries which get
washed during the manufacturing processes and create pollution.
Sludge:
• Sledges are the product of biological treatment of waste water. Sludge
comprise solids found in waste water plus organism used in the treatment
process.

6/11/2020
Nature of the effluent
depends on
pH
Temperature
Total suspended
solids (TSS)
Total dissolved
solids(TDS)
Biological oxygen
demands(BOD)
Chemical oxygen
demands(COD)

POLLUTION PROBLEMS IN TEXTILE INDUSTRY
Color
• Presence of color in the waste water is one of the main problems in
textile industry.
• Colors are easily visible to human eyes even at very low concentration.
Hence, color from textile wastes carries significant aesthetic importance.
• Most of the dyes are stable and has no effect of light or oxidizing agents.
• They are also not easily degradable by the conventional treatment
methods.
• Removal of dyes from the effluent is major problem in most of textile
industries.

Dissolved Solids:
• Dissolved solids contained in the industry effluents are also a critical
parameter.
• Use of common salt and glauber salt etc. in processes directly increase
total dissolved solids (TDS) level in the effluent.
• TDS are difficult to be treated with conventional treatment systems.
• Disposal of high TDS bearing effluents can lead to increase in TDS of
ground water and surface water.

Toxic Metals
• Waste water of textiles is not free from metal contents. There are mainly
two sources of metals.
• The metals may come as impurity with the chemicals used during
processing such as caustic soda, sodium carbonate and salts.
• The source of metal could be dye stuffs like metalised mordent dyes. The
metal complex dyes are mostly based on chromium.

Others
• Textile effluents are often contaminated with non-biodegradable organics
termed as refractory materials.
• Detergents are typical example of such materials. The presence of these
chemicals results in high chemical oxygen demand (COD) value of the
effluent.
• Organic pollutants, which originate from organic compounds of dye stuffs,
acids, sizing materials, enzymes, tallow etc are also found in textile
effluent, Such impurities are reflected in the analysis of bio-chemical
oxygen demand (BOD) and COD.

Categorization of Waste Generated in
Textile Industry
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• 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:
Categorization
of Waste textile
industry
Hard to Treat
Wastes
Hazardous or Toxic
Wastes
High Volume
Wastes
Dispersible Wastes

1. 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:
• Colour & metal and dyeing operation
• Phosphates - preparatory processes and dyeing
• Non-biodegradable organic materials ,surfactants
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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
• 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.6/11/2020

Dispersible Wastes
• The following operations in textile industry generate highly
dispersible waste:
• 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)

Classification of waste water
treatment process
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WASTE WATER FROM
DIFFERENT PROCESS

Primary Treatment
• After the removal of gross solids, gritty materials and excessive
quantities of oil and grease, the next step is to remove the
remaining suspended solids as much as possible.
• This step is aimed at reducing the strength of the waste water
and also to facilitate secondary treatment.
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PRIMARY TREATMENT
SCREENING SEDEMENTATION EQUALIZATION
NEUTRALIZATIONCHEMICAL
COGULATION
MECHNICA
FLOCCULATION
PRIMARY
SCREENING
SEDIMENTATION
EQUALIZATION
NEUTRALIZATION
CHEMICAL
COGULATION
MECHNICAL
FLOCCULATION

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.
• The suspended fibres have to be removed prior to secondary
biological treatment; otherwise they may affect the secondary
treatment system.
• They are reported to clog trickling filters, seals or carbon beads.

Sedimentation:
• The suspended matter in textile effluent can be removed
efficiently and economically by 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.
• The most common equipment used includes horizontal flow
sedimentation tanks and center-feed circular clarifiers.
• The settled sludge is removed from the sedimentation tanks by
mechanical scrapping into hoppers and pumping it out
subsequently.

Equalization:
• Effluent streams are collected into ‘sump pit’. Sometimes mixed
effluents are stirred by rotating agitators or by blowing compressed air
from below.
• The pit has a conical bottom for enhancing the settling of solid particles.
Neutralisation:
• Normally, pH values of cotton finishing effluents are on the alkaline
side.
• Hence, pH value of equalized effluent should be adjusted.
• Use of dilute sulphuric acid and boiler flue gas rich in carbon dioxide are
not uncommon.
• Since most of the secondary biological treatments are effective in the
pH 5 to 9, neutralization step is an important process to facilitate.

Chemical coagulation and
Mechanical flocculation
• Finely divided suspended solids and colloidal particles cannot be
efficiently removed by simple sedimentation by gravity.
• In such cases, mechanical flocculation or chemical coagulation is
employed.
• Specialized equipment such as clariflocculator is also available,
wherein flocculation chamber is a part of a sedimentation tank.
• In order to alter the physical state of colloidal and suspended
particles and to facilitate their removal by sedimentation, chemical
coagulants are used.
• It is a controlled process, which forms a floc (flocculent precipitate)
and results in obtaining a clear effluent free from matter in
suspension or in the colloidal state.6/11/2020

The degree of clarification obtained also depends on the quantity of
chemicals used. In this method:
• 80-90% of the total suspended matter,
• 40-70% of BOD,
• 30-60% of the COD
• and 80-90% of the bacteria can be removed.
Most commonly used chemicals for chemical coagulation are alum,
ferric chloride, ferric sulphate, ferrous sulphate and lime.

Secondary Treatment
• The main purpose of secondary treatment is to provide BOD
removal beyond what is achievable by simple sedimentation.
• It also removes appreciable amounts of oil and phenol.
• In secondary treatment, the dissolved and colloidal organic
compounds and colour present in waste water is removed or
reduced and to stabilize the organic matter.
This is achieved biologically using bacteria and other
microorganisms. Textile processing effluents are amenable for
biological treatments.
These processes may be:
• aerobic or
• anaerobic.6/11/2020

• In Aerobic Processes, bacteria and other microorganisms
consume organic matter as food.
• They bring about the following sequential changes:
• Coagulation and flocculation of colloidal matter Oxidation of
dissolved organic matter to carbon dioxide Degradation of
nitrogenous organic matter to ammonia, which is then converted
into nitrite and eventually to nitrate.
• Anaerobic Treatment is mainly employed for the digestion of
sludge.
• The efficiency of this process depends upon pH, temperature,
waste loading, absence of oxygen and toxic materials.
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SECONDARY TREATMENT
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SECONDARY
AERATED LAGOON
TRICKLING
FILTRATION
ACTIVATED SLUDGE
PROCESS
OXIDATION
DITCH /POND
AERATED
LAGOON
TRICKLING ACTIVATED
FILTRATION SLUDGE
OXIDATION
DITCH / POND

Aerated lagoons:
• These are large holding tanks or ponds having a depth of 3-5 m
and are lined with cement, polythene or rubber.
• The effluents from primary treatment processes are collected in
these tanks and are aerated with mechanical devices, such as
floating aerators, for about 2 to 6 days.
• During this time, a healthy flocculent sludge is formed which
brings about oxidation of the dissolved organic matter.
• BOD removal to the extent of 99% could be achieved with
efficient operation.
• The major disadvantages are the large space requirements and
the bacterial contamination of the lagoon effluent, which
necessitates further biological purification.

Trickling filters:
• The trickling filters usually consists of circular or rectangular
beds, 1 m to 3 m deep, made of well-graded media (such as
broken stone, PVC, Coal, Synthetic resins, Gravel or Clinkers) of
size 40 mm to 150 mm.
• On prepared bed, wastewater is sprinkled uniformly on the entire
bed with the help of a slowly rotating distributor (such as rotary
sprinkler) equipped with orifices or nozzles.
• Thus, the waste water trickles through the media. The filter is
arranged in such a fashion that air can enter at the bottom;
counter current to the effluent flow and a natural draft is
produced.

Activated sludge process:
• This is the most versatile biological oxidation method employed for the
treatment of waste water containing dissolved solids, colloids and
coarse solid organic matter.
• In this process, the waste water is aerated in a reaction tank in which
some microbial flock is suspended.
• The aerobic bacterial flora bring about biological degradation of the
waste into carbon dioxide and water molecule, while consuming some
organic matter for synthesizing bacteria.
• The bacteria flora grows and remains suspended in the form of a floc,
which is called “Activated Sludge”. The effluent from the reaction tank
is separated from the sludge by settling and discharged.
• An efficient aeration for 5 to 24 hours is required for industrial wastes.
BOD removal to the extent of 90-95% can be achieved in this process.

Oxidation ditch:
• This can be considered as a modification of the conventional
Activated Sludge process.
• Waste water, after screening in allowed into the oxidation ditch.
• The mixed liquor containing the sludge solids is aerated in the
channel with the help of a mechanical rotor.
• The usual hydraulic retention time is 12 to 24 hrs and for solids, it
is 20-30 days.
• Most of the sludge formed is recycled for the subsequent
treatment cycle.
• The surplus sludge can be dried without odour on sand drying
beds.

Oxidation pond:
• An oxidation pond is a large shallow pond wherein stabilization of
organic matter in the waste is brought about mostly by bacteria
and to some extent by protozoa.
• The oxygen requirement for their metabolism is provided by
algae present in the pond. The algae, in turn, utilize the CO2
released by the bacteria for their photosynthesis.
• Oxidation ponds are also called waste stabilization ponds.

Tertiary Treatment Processes
• It is worthwhile to mention that the textile waste contains
significant quantities of non-biodegradable chemical polymers.
Since the conventional treatment methods are inadequate, there is
the need for efficient tertiary treatment process.
• Oxidation techniques: A variety of oxidizing agents can be used to
decolorize wastes. Sodium hypochlorite decolourizes dye bath
efficiently. Though it is a low cost technique, but it forms
absorbable toxic organic halides (AOX) .
• Ozone on decomposition generates oxygen and free radicals and
the later combines with colouring agents of effluent resulting in the
destruction of colours .
• The main disadvantage of these techniques is it requires an
effective sludge producing pretreatment.6/11/2020

TERTIARY TREATMENT
6/11/2020
TERTIARY
OXIDATION TECHNIQUE
OXIDATION
TECHNIQUE
ELECTROLYTIC
PRECIPITATION & FOAM
FRACTIONATION
MEMBRANE
TECHNOLOGIES
MEMBRANE
TECHNOLOGIES
ELECTROCHEMICAL
PROCESSES
ION EXCHANGE
ION
EXCHANGE
PHOTO CATALYTIC
DEGRADATION
ADSORPTION
PHOTO CATALYTIC
DEGRADATION
ADSORPTION
THERMAL EVAPORATION THERMAL EVAPORATION
ELECTROCHEMICAL
PROCESSES
ELECTROLYTIC
PRECIPITATION & FOAM
FRACTIONATION

Electrolytic precipitation & Foam fractionation
• The mechanism by which synthetic organic polymer removes
dissolved residual dyes from effluents is best described in terms of the
electrostatic attraction between the oppositely charged soluble dye
and polymer molecules.
• Many of the most problematic dye types, such as reactive dyes, carry a
residual negative charge in their hydrolysed dissolved form, and so
positively charged groups on the polymers provide the necessary
counter for the interaction and subsequent precipitation to occur.
• The immediate result of this co-precipitation is the almost
instantaneous production of very small coloured particles, having little
strength and breaking down at any significant disturbances.
• The agglomeration of the coloured precipitates by using appropriate
high polyelectrolyte flocculants produces stable flocs.

Electro chemical processes:
• It has lower temperature requirement than those of other
equivalent non-electrochemical treatment and there is no need
for additional chemical.
• It also can prevent the production of unwanted side products.
But, if suspended or colloidal solids were high concentration in
the waste water, they impede the electrochemical reaction.
• Therefore, those materials need to be sufficiently removed
before electrochemical oxidation

Ion exchange method:
• This is used for the removal of undesirable anions and cations
from waste water.
• It involves the passage of waste water through the beds of ion
exchange resins where some undesirable cations or anions of
waste water get exchanged for sodium or hydrogen ions of the
resin .
• Most ion exchange resins now in use are synthetic polymeric
materials containing ion groups such as sulphonyl, quarternary
ammonium group etc.

Photo catalytic degradation:
• An advanced method to decolourize a wide range of dyes depending
upon their molecular structure.
• In this process, photoactive catalyst illuminates with UV light, generates
highly reactive radical, which can decompose organic compounds.
Adsorption:
• It is the exchange of material at the interface between two immiscible
phases in contact with one another.
• Adsorption appears to have considerable potential for the removal of
colour from industrial effluents.
• Owen (1978) after surveying 13 textile industries has reported that
adsorption using granular activated carbon has emerged as a practical
and economical process for the removal of colour from textile effluents.

Thermal evaporation:
• The use of sodium per sulphate has better oxidizing potential
than NaOCl in the thermal evaporator.
• The process is ecofriendly since there is no sludge formation and
no emission of the toxic chlorine fumes during evaporation.
• Oxidative decolourisation of reactive dye by persulphate due to
the formation of free radicals has been reported in the literature .

Membrane filtration
• Membrane filtration offers potential applications:
• Processes using membranes provide very interesting possibilities
for : the separation of hydrolyzed dye-stuffs and dyeing auxiliaries
simultaneously reduce coloration and BOD/COD of the
wastewater used to treat reactive dye bath effluent,
• reduce waste volume and simultaneously recovering salt
• The advantages of membrane filtration are because it is a quick
method with low spatial requirement and the saturate can be
reused.
• The disadvantage with the membrane filtration method that it
has a limited life time before membrane fouling occurs and the
cost is also high.

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• Reverse osmosis
membranes have a retention
rate of 90% or more for most types of
ionic compounds and produce a high
quality of permeate .
• Decoloration and elimination of
chemical auxiliaries in dye house
wastewater can be carried out in a
single step by reverse osmosis.
• Reverse osmosis permits the
removal of all mineral salts,
hydrolyzed reactive dyes, and
chemical auxiliaries.
• Greater the energy is required for
process of the separation of higher
concentration of dissolved salt.
Microfiltration
Ultrafiltration
Nano filtration
Reverse
Osmosis
Membrane
filtration

• Nanofiltration has been applied for the treatment of colored
effluents from the textile industry. A combination of adsorption
and nanofiltration can be adopted for the treatment of textile dye
effluents.
• Ultrafiltration enables elimination of macromolecules and
particles, but the elimination of polluting substances, such as
dyes, is never complete it is only between 31% and 76%.
• Microfiltration is suitable for treating dye baths containing
pigment dyes as well as for subsequent rinsing baths. The
chemicals used in dye bath, which are not filtered by
microfiltration, will remain in the bath. Microfiltration can also be
used as a pretreatment for nanofiltration or reverse osmosis

Advantages and disadvantages of different
effluent treatment processes
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