Appropriate Effluent Treatment
System for Dyes and Dyeintermediates Industries
PROF. ARUNABHA MAJUMDER
Emeritus Fellow
School of Water Resources Engineering
Jadavpur University
and
Ex-Director-Professor
All India Institute of Hygiene and Public Health, Kolkata
Background

Dyes and dye- intermediates Industries: Designated as ‘ Special Red’
Category Industry

As per Industrial siting (Locational) Policy for West Bengal, Special red
Category Industries cannot be permitted to be operated in municipal areas
falling under Kolkata Metropolitan Area (KMA).

Dyes and Dye-intermediates Industries are restricted / prohibited within the
belt of 10 km radius around the periphery of the Leather Complex at
Bantala.

Fabric dyeing is carried out by either in continuous or batch
process.

In the continuous dyeing process, the dye is transferred to the
fabric by passing the fabric across roller which are partially
submerged in the dye solution.

A batch dyeing of fabric is often accomplished in atmosphere
or pressure backs or in jet dyeing machines. The majority of
knitted fabric are batch dyed, using a variety of processes.

Direct dyes
 Basic dyes
 Vat dyes
 Sulphur dyes
 Developed dyes
 Napthol dyes
 Metal Complex dyes

Direct dyes: These dyes are neutral and are used for dyeing of cotton
textiles on account of its natural affinity to this class of dyes, which are
easy to apply without any mordants. The colors produced are stable
and are fast to light.

Basic dyes: These are salts of colored base
and require an acid
mordant such as tannic acid, tartaric and acetic acids. These dyes
impart very bright colors to the fabrics. Soluble oil and soda ash are
also used in the final stages of dyeing with basic dyes. A number of
waste streams and other process chemicals are generated during the
process.

Vat dyes: This group of dyes are fast dyes and are not water soluble, but are rendered
soluble by strong reducing agents like sodium hydrosulphite. In this process the cloth is
immersed in a vat containing the dye, dilute acid and sodium hydrosulphite and then
exposed to oxidation in presence of an oxidizing agent. This is followed by scouring with
a dilute alkaline solution to neutralize the excess acid.

Sulfur dyes: These contain sulfur compounds and are applied together with a suitable
reducing agent like sodium sulfide followed by oxidation.

Developed dyes: These are colors which are produced on the fiber. At first the color is
directly applied on the fabric and is converted into an unstable azodye by the addition of
sodium nitrite and HCl. Next the stable form of the color is developed on the fiber by the
action of beta napthol.

Napthol dyes: In this process the color is developed by a reversal of the
sequence of operations of the dyeing with developed colours, the cloth
is at first treated with beta-napthol and then diazotised with sodium
nitrite and HCl. A hot soap and soda bath is used.

Metal complex dyes: In the case of certain types of cotton fabrics and
synthetic textiles like nylon and polyester, dyeing process is carried out
by depositing inside the fibre complex
salts of iron and chromium.
Depending on the quantity of the metal salts and various shades khaki
colour can be produced. Metallic salts are also used as catalysts for the
application of wash and wear permanent press and water repellant and
flame retardant finishes.
General Characteristics of dye house
waste water
pH
 TDS
 Suspended Solids (SS)
 BOD
 COD

6.3 to 10.5
680 – 3180 mg/l
380 – 950 mg/l
320 – 820 mg/l
750 – 2000 mg/l
Effluent Treatment process
Coagulant
/Lime/flocculant
1
2
11
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Screen
Equilisation Tank
Flush Mixer
Primary Clarifier
Bio-reactor/AT
Secondary Clarifier
Sump
Active Carbon Filter
Sludge dewatering
Sludge thickener
SDB
4
5
3
10
9
6
8
7
Final Effluent
Filter
Recycle/Reuse
Primary Treatment

By the process of coagulation- flocculation and
sedimentation, color, colloidal, suspended and
settleable solids are removed

Flush mixing for 60 to 90 sec

Slow mixing for 20 to 25 minutes

Detention time in PC : 150 min

BOD and COD reduction: 45 to 65 %

Bio-reactor with Conventional or Extended aeration

Detention time:
Conventional
: 6 hrs to 10 hrs
Extended Aeration

: 12 hrs to 24 hrs(18 to 36 hrs)
Aeration System: Combined system of diffused and surface aeration. Additional
oxygenation capacity of the aerators in the tune of 30% to 40% need to be
considered. D.O of 1.0 to 1.5 mg/l is to be maintained in the Reactor.

Return Sludge Pump: at least 3 (three) pumps are necessary for maintaining
optimum MLSS in the reactor

Regular Sludge wasting is compulsory and must be regular

BOD and COD removal in Secondary treatment: 85-95%

Regular monitoring and surveillance

Filtration options
– Sand and Gravel
– Activated Carbon-sand-gravel
– Ultra-filtration
– Nano-filtration
– Ceramic Membrane Filtration
– Reverse osmosis

Sludge Management
– Sludge dewatering
– Sludge thickening
– Sludge drying bed
Effluent treatment plant performance depends on:

Proper wastewater neutralization through uniform mixing in the
equilization tank

Optimization of coagulant and flocculant dosage based on treatability
studies.

Proper dosing by providing dosing tank instead of manual operation.

Regular de-sludging from Primary Clarifier and Secondary Clarifier

Build up of design MLSS concentration in the A.T of biological
treatment process

Replacement of media in the tertiary treatment column.
Schematics of Advanced Treatment System
Rejects
P
Multigrade
Filter
UF
Secondary
Effluent
UF
Permeate
sump
P
RO
Permeate
Rejects
1.
Activated Sludge process (Conventional)
2.
Trickling Filter
3.
Rotating biological Contactor
4.
Extended Aeration
5.
Aerated Lagoon
6.
UASB
7.
UFAF / HFAB / UAFB
Case Study: Common Effluent Treatment Plant
(CEPT) for proposed Garment and Textile Park,
Maheshtala
Total Unit: 292
Unit handling 225 kg/day
= 159
Unit handling 450 kg/day
=138
Water requirement for 159 units 225 kg/day X 50 lts/kg X 159
= 1788750 lts/day
Water requirement for 138 units = 450 kg/day X 50lts/kg X 138
= 3105000 lts/day
Case Study: Common Effluent Treatment Plant
(CEPT) for proposed Garment and Textile Tank,
Maheshtala (Contd.)
Industrial water requirement
= 4893750 lts/day
Adding 7.5 % extra, Industrial Waste Water
= 5260781 lts/day
Waste Water generation (90% of Water requirement)
= 4.80 MLD
Domestic sewage generation
= 0.20 MLD
ETP design capacity
= 5.0 MLD
Characteristics of raw wastewater for
different dying units
Average Characteristics of Units
Sl. No
Parameters
Unit I
Unit II
Unit III
Average
1
pH
9.5
9.2
10.5
9.73
2
COD mg/L
554
915
1025
831
3
BOD mg/L
270
470
552
431
4
TSS mg/L
300
280
220
267
Unit Design
1. Volume of Equalization Tank
= 834 m3
Size = 26 m X 13 m X 3 m
2. Chemical mixing flush Tank
Detention time
= 120 sec
Size
= 3 m X 2.5 m X 1.5 m
Chemical to be added:
Alum
= 300 mg/L
PAC
= 150 mg/L
Lime
= 60 mg/L

Primary Clarifier ( 2 Nos )
Diameter
= 14 m
Depth
= 3.5 m
Over flow rate
= 25 m3 /m2/day
Detention time
= 4.2 hrs
Weir loading rate
= 57.32 m3/m/day

Aeration Tank (Baffeled-4.5m wide) ( 2 Nos )
Length
= 18.7 m
Breath
= 16.4 m
Depth
= 3.5 m
Detention time
= 8hrs
F/M ratio
= 0.24
MLSS
= 3000 mg/L
Surface aerator
= 4 numbers@10 HP
Diffused Aeration System : In addition


Secondary Clarifier ( 2 Nos )
Diameter
= 13 m
Depth
=3m
Detention time
= 3.16 hrs
Surface over flow rate
= 3.16 hrs
Sludge Thickener ( 2 Nos )
Gravity thickener with Continuous flow type
Two thickeners of 2 m diameter and 3 m depth are to be
provided
Vacuum filter ( 2 N0s )
Two vacuum filters to operate at 10 kg/m2/hr
Land Requirement to treat 5 MLD effluent : 4500 sq.m.( 500 sq.m/MLD)

Conclusion





The ETP for treatment of dye effluent need to be
designed on the basis of treatability test atleast in bench
scale level.
Both chemical and biological treatment are to be carried
at bench scale level
Chemical doses are to be finalised as per raw effluent
quality
The bio-reactor is to be stabilized with specific biomass
in dye effluent
Design F/M ratio, MLSS, MLVSS, D.O, sludge wasting,
return sludge etc. are to be maintained during operation
of ETP
Conclusion( Contd.)

Wastewater quality monitoring and surveillance
are to be carried out regularly
 Tertiary treatment with different filtration system
may be adopted as per requirement
 Proper housekeeping should be maintained in
the ETP
 The Plant Operators / Supervisors must be
trained
THANK YOU