Zero Discharge Possibility in Textile Processing Industry

Introduction

Zero discharge implies that the process water utilized in pretreatment, bleaching and dyeing operations is recovered for reuse to an extent that there is no discharge of effluent into the environment.

Design Considerations1. Quantity of the effluent to be treated.2. Variation of quantity and quality with

time3. Unit processes suitable for achieving

desired purposes for the given effluent. 4. The upper and lower limits of

performance of each unit process.5. The durability of the system to be

adopted.6. The feasibility of establishing suitable

collection and conveyance system

Qualitative Analysis of Textile Effluent• Typical BOD5 : COD values lie between 1:2.5 and

1:5. • Organic load from pretreatment: BOD5 values:

Desizing - up to 140 kg O2 per tonne of material alkaline boiling out of polyester – cotton blend

fabrics - 210 kg/t. • High COD values because of the organic or

inorganic reducing agents used. • High TDS due to large quantities of salts used in

dye baths• Trace metals like Cu, Zn, Pb, Ni, Cd (few μgrams

per gram)• Chemicals : wetting agents, soda ash, peroxides,

bleaching powder, common salt, acids, dye stuffs, soap oil and, fixing and finishing agents

Characteristics of effluents from different sectors of textile industryCharacteristics

Cotton Synthetic Wool Scouring

pH 8-12 7-9 3-10

BOD 150-750 150-200 5000-8000

COD 200-2400 400-650 100000-200000

Alkalinity 180-7300 550-630 80-100

Phenol 0.03-1 - -

Oils and Grease 4.5-30 - 2000-2500

SS 35-1750 50-150 5000-6000

TDS 2100-7100 1060-1080 100000-130000

Requirements to establish a zero discharge system1. Assessment of existing treatment based on

available information2. The chosen treatment system

i) should be able to produce effluent with desired quality

ii) should not produce any harmful substances on its own.

3. Conduct pilot plant test runs4. Full-scale design should only be based on the

combined effluent characteristics of all member units.

5. Pipeline design for effluent transport and return of treated effluent to the member units from the CETP

6.Identification of processes that generate the effluent alongwith the chemicals and their quantities utilized

7. Listing energy conserving measures to reduce operating costs.

8. Conducting levelling survey is very much essential to design the pipeline – both for implementing gravity flow as well as for pumped flow.

9. The system should consider ways of handling undesirable situations : i) feed with undesirable quality, ii) power failure, iii) periods of maintenanceiv) flooding.

Collection and Conveyance1. Available location for the treatment facility, extend of

land available, and the possibility for further expansion

2. Levelling survey to estimate the latitude, longitude and, height of each member unit and that of the proposed CETP

3. Estimation of quantity of effluent generated per day in each member unit

4. Estimating the available storage capacity of effluent storage tanks at each member unit

5. Provision for removal of debris, grits, and suspended solids should be given at each member unit

6. Capacity of the pipeline material to withstand the temperature range of effluent

7. Durability of the material of construction of the pipeline.

8. Proposed pipeline route with a list of existing

natural and man-made impediments

9. Accessibility to road, availability of electric power, provision for secured landfill, proximity to urban population and archaeological treasures

10. Implementation of gravity flow and/or pumped flow depending on the prevailing environmental conditions.

Treating Segregated and Combined Raw Effluent1. Treating only the quantity of effluent generated in

that process.

2. Due to segregation, each type of effluent has to be stored in separate tanks at each member units, and passed through a separate pipeline to the CETP.

3. Employment of different unit processes and equipments

4. As the temperature of the dye bath is around 70-80°C, it takes more time for natural cooling when compared with combined raw effluent.

5.The organics content of the recovered water utilizing combined raw effluent is comparatively lower than in the case of segregation.

6. When dye bath is directly treated with an evaporator there might be a problem in colour removal since chlorine is used.

The only disadvantage with handling combined raw effluent is that a large volume has to be handled. However, considering the benefits, it is always desirable to treat combined raw effluent instead of engaging segregation.

Unit Processes1. Removal of grits and suspended solids2. Removal of oil & grease3. Equalization4. Adjustment of pH5. Reduction of BOD/COD6. Removal of colour7. Recovery of reusable water8. Treatment of reject (from reverse osmosis

system/blow out from evaporator)9. Solid waste disposal and management.

Primary Treatment

1. Removal of grits and suspended solids

2. Removal of oil & grease

3. Equalization

4. Adjustment of pH

5. Reduction of BOD/COD

6. Removal of colour

Selection of Biological Process:

i) Simple Aeration

ii) Activated Sludge Process with/without aeration

iii) Aerobic/anaerobic digestion with Fluidised Bed Bioreactor (FBBR)

iv) Membrane Bioreactor (MBR)

Problems associated with Conventional Biodegradation Process1. Most dyestuffs are non-biodegradable2. High TDS (8000-10000ppm) retards

microbial growth3. Low F/M ratio4. Low biological activity5. Different biodegradability of different

dye stuffs 6. Higher sludge production7. Inefficient nutrient removal from raw

effluent which encourages microbial growth on RO membrane used in secondary treatment

Membrane BioreactorInvolves conventional activated sludge process with the use of ultrafiltration or, microfiltration membrane which helps to maintain higher levels of MLSS concentration

Retention of active microorganisms, extra cellular enzymes generated by these micro-organisms for degradation of the organics present in the effluent, organics resulting from cell-lysis, and other heavy molecular weight organics typical of textile effluent.

Thus, overall efficiency of BOD-COD removal is increased

Submerged MBRs are generally used in textile waste-water treatment. It incorporates two zones:1. Anoxic2. Aerobic

Advantages:1. Reduces the foot print 2. Improves BOD/COD reduction3. Eliminates the need for a secondary clarifier4. Removes suspended solids5. Gives uniform output of effluent6. Can be operated at higher MLSS

concentration7. Reduces shocks

Disadvantage:High capital investment

Removal of colour and turbidity:1. Chlorination2. Ozonation3. Activated Carbon Filter (ACF)4. Pressure Sand Filter (PSF) and ACF

used to remove turbidity

Secondary Treatment

Secondary TreatmentGenerally reverse osmosis membranes are

employed

Design Considerations1. Should be able to operate with the desired TDS level

typical of the effluent.

2. Should be able to withstand membrane scaling caused by various constituents in the effluent.

3. It is essential to utilize highly optimized system in place.

4. In order to reduce membrane fouling and backwash frequency, fouling resistant membranes may be utilized.

5. Mixing desired quantity of permeate with the feed and recirculating it through the membrane system is another option to maintain system performance.

Tertiary Treatment

Tertiary Treatment

Objective of a tertiary treatment system is to treat the reject generated by the reverse osmosis system.

The tertiary system employs an evaporator that utilizes steam as heating source, produces reusable water in the form of condensate, and generates blow down and salt as by products.

Design Considerations1. For good maintenance, an evaporator

has to be cleaned regularly. 2. The design of secured landfill should

take into account disposal of the salt recovered from the evaporator.

3. The evaporator design should consider utilization of waste heat from the steam.

4. The blow down from evaporator has to be treated with a solar evaporation pond.

CASE STUDY Manickapurampudur

Common Effluent Treatment Plant,

Tirupur, Tamil Nadu

Tirupur Textile industry: An Overivew• Leading cotton knitwear industrial cluster

• Favorable climatic conditions

• Experienced rapid growth in the last two decades Operation of textile

industryNo. of units

Knitting and stitching 4900Dyeing and bleaching 736

Printing 300Embroidery 100

Other 200TOTAL 6250

Issues•  Ground water quality in Tirupur was

significantlyaffected due to the discharge of large

quantities oftextile dye effluent into the Noyyal river

• Contamination of Orathupalayam Dam causing serious environmental degradation in the downstream areas of Erode and Karur.

Observations and Measures•Treated effluent regularly analysed for :

pH, TSS, TDS, COD, BOD, Chloride, Sulphate, and trace metals

•Found that the TDS levels in Noyyal is now oscillating in the range of 3,400 to 4,200 ppm

•Attempts were made to evaporate the effluentusing solar energy

•Trials conducted for implementing reverse osmosis system

•Pilot study was carried out for a week using Vibratory Shear Enhanced Process (VSEP) reverse osmosis

•Produced reusable water with a Total Dissolved Solids (TDS) < 500 mg/L

•Also, eliminates chemicals in the pretreatment process

Present scheme of effluent treatment at MPCETP, Tirupur

•Raw effluent passed to equalization tank

▫Aeration

•Clariflocculator

▫Sludge to evaporation Ponds▫Treated effluent to sand bed

Implementation of Zero-Dischargea)Reverse Osmosis (R.O) system for

treating 2000 m/day of textile dye effluent for recovery of pure water for reuse in textile wet processing.

b)Nano-Filtration (N.F) assembly for salt recovery from R.O. reject and its reuse in dyeing/other industries.

c)Multiple Effect Evaporator for recovery of reusable water from 200 m/day of reject from nano filtration assembly.

d) Solar pond for evaporation of mother liquor from Multiple Effect Evaporator, and separation of salts.

e) Windmills for power generation to cater to the needs of the reverse osmosis, nanofiltration, and other electrical appliances of the Common Effluent Treatment Plant

In addition, currently existing private forest of 5 acres will be expanded to 20 acres in order to promote environmental benefits.

Thank You