1. Appropriate Effluent Treatment System for Dyes and Dye-intermediates 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

2. 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.

3. 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.

4. Salient features of the dyeing process with different classes of dyes
Direct dyes
Basic dyes
Vat dyes
Sulphur dyes
Developed dyes
Napthol dyes
Metal Complex dyes

5. Dyeing Processes
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.

6. Contd.
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.

7. Contd.
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.

8. General Characteristics of dye house waste water
pH to 10.5
TDS – 3180 mg/l
Suspended Solids (SS) 380 – 950 mg/l
BOD – 820 mg/l
COD – 2000 mg/l

9. Effluent Treatment process
Coagulant
/Lime/flocculant 4 5 1 2 3 11 10 9
Screen
Equilisation Tank
Flush Mixer
Primary Clarifier
Bio-reactor/AT
Secondary Clarifier
Sump
Active Carbon Filter
Sludge dewatering
Sludge thickener
SDB 8 6 7
Final Effluent
Filter
Recycle/Reuse

10. 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 %

11. Secondary Treatment 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

12. Tertiary Treatment Filtration options Sludge Management
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

13. Effluent Treatment Plant Performance
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.

14. Schematics of Advanced Treatment System
Rejects
Multigrade
Filter UF P UF
Permeate
sump P
Secondary
Effluent
Permeate RO
Rejects

15. Biological Treatment Alternatives
Activated Sludge process (Conventional)
Trickling Filter
Rotating biological Contactor
Extended Aeration
Aerated Lagoon
UASB
UFAF / HFAB / UAFB

16. 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
= lts/day
Water requirement for 138 units = 450 kg/day X 50lts/kg X 138
= lts/day

17. Case Study: Common Effluent Treatment Plant (CEPT) for proposed Garment and Textile Tank, Maheshtala (Contd.)
Industrial water requirement
= lts/day
Adding 7.5 % extra, Industrial Waste Water
= lts/day
Waste Water generation (90% of Water requirement)
= 4.80 MLD
Domestic sewage generation
= 0.20 MLD
ETP design capacity
= 5.0 MLD

18. 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

19. 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

20. 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 = m3/m/day

21. 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 HP
Diffused Aeration System : In addition

22. Secondary Clarifier ( 2 Nos )
Diameter = 13 m
Depth = 3 m
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)

24. 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

25. 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

26. THANK YOU