The textile dyeing is one of the highly polluting industries in India. The Tirupur Textile dyeing cluster in the State of Tamilnadu is considered an environmental hot spot due to serious and adverse impact on the local environment particularly the Noyyal River and agriculture. The Tamilnadu Pollution Control Board (TNPCB) has directed the industry to implement the Zero Liquid Discharge (ZLD) based effluent recycling system in order to ensure no effluent treated or otherwise is discharged to the river. In order to comply with this direction the industry set up Individual Effluent Treatment Plants (IETPs) and Common Effluent Treatment Plants (CETPs) based on the ZLD concept. The wastewater treatment scheme in these plants essentially involved the Physical-chemical- biological treatment of the Textile dyeing wastewater followed by Reverse Osmosis (R.O) for recovery of water (permeate). The concentrated brine from the Reverse Osmosis unit was then Evaporated and crystallized using Multiple Effect Evaporators (MEE) to obtain salt to achieve Zero Liquid Discharge. However, several problems were and are being faced in evaporation and crystallization of the brine, which essentially is a mixed salt with several contaminants including Organics, Colour, Silica, Hardness. The problems associated with Evaporation & Crystallization has seriously affected effluent processing volumes of the Effluent Treatment Plants and achieving of Zero liquid Discharge norms set by the Regulatory authorities. We have avoided the above problem by "treated brine re-use technology", wherein "treated brine" from Reverse Osmosis and/or Mechanical Vapour Recompression type Evaporator (MVR-E) was used in Textile dyeing, avoiding the need for crystallization using a MEE. The treated brine is re-used by the dyeing unit in their dye bath directly instead of adding fresh salt to the dye bath along with the various colour dyes. The treated brine should meet the following criteria to be re-used by Textile Dyeing industry in the dye baths:

1. Volume of brine should be less than the dye bath volume (Typical Dye bath volume is 10% of the total effluent volume).

2. Should be free from contaminants such as Colour and Organics, so that the brine cannot be used for any colour or shade and the quality of dyeing matches with their requirements.

3. Should have low hardness (lower than the hardness in fresh water used currently for dyeing).

4. Concentration of salt in the treated dye bath to match with required concentration of salt for different shades.

5. Usage of treated brine from the Effluent Treatment Plant should not result in the need for larger quantities of dye stuff to achieve the same colour or shade.
However, the use of Evaporators and Crystallizer for management of rejects has not been successful for various reasons including:

1.1 Difficulties in crystallization of mixed salts (e.g. Sodium Chloride, Sodium sulphate, Calcium Sulphate, Calcium Chloride, Magnesium Sulphate, Magnesium Chloride) typical of saline wastewater.

1.2 Presence of foulants such as Hardness, Silica and Organics results in scaling and choking
of Evaporators resulting in reduced efficiency, longer downtime and higher operating costs.

1.3 Issues of Corrosion due to high Chlorides, temperature and water resulting in reduced life of machinery and need for exotic metallurgy in construction.

1.4 Very high operating costs, typically Rs. 350 to Rs. 500/ m3 of feed effluent (R.O rejects) making operation of Zero Discharge systems unviable or unsustainable. The Evaporators are high power guzzlers and require generation of large quantity of steam through burning of firewood and coal.

1.5 Despite all the above issues, the salt crystallized out is contaminated (with Hardness, Silica, Colour, Organics) making it unfit for reuse.

1.6 The contaminated salt crystallized as mentioned above has become a very serious disposal issue. As Salt cannot be disposed of to Landfills (meant for other types of Solid and Hazardous wastes which be immobilized safely) or to sea (due to pollution issues) this has created a huge storage and disposal problem. This in turn has led to inadvertent or clandestine disposal of such waste salts.
Our proposed alternative based on reuse of treated brine in textile dyeing CETPs, without the need for evaporation and crystallization, solves all the above mentioned problems and also returns a valuable resource (salt) back to industry for use in their dyeing process. 2. Advantages of the invention

i. A Flexible and robust system for achieving 'Zero Liquid effluent Discharge' in Textile Dyeing Industry. Successfully demonstrated in Plant scale,
ii. Drastic reduction in use of MVR Evaporator system for R.O rejects management (from 26% v/v to < 12% v/v of inflow). Reduction or avoidance of usage of MEE (from 7-8% to less than 2%.

ii. Elimination of Resin and Softener regenerate liquor for evaporation,

iv. Reduction/ Elimination in generation of waste mixed salt from Resin and Softener regenerate liquor evaporation for disposal to Hazardous landfill,

v. Reduction in O&M cost by due to drastic reduction in liquors to be evaporated.

vi. Flexibility in use of sodium chloride based or sodium sulphate for dyeing (both salts can be used for dyeing) as the brine treatments system is not affected by it unlike an Evaporator.

ii. Use of existing MVR-E with minimal modifications to handle excess rejects after brine
usage. nil. Reduced time to achieve Zero Liquid Discharge.

3. Detailed description of the process relating to the invention with maximum workable ranges of parameters

The objective of our 'treated brine reuse technology" is to develop a process is to achieve treated liquid brine with low hardness, low colour, low organics and maximum salt concentration. The following improvements, modifications and additions were done to the existing CETP process to achieve the above objectives:

3.1 Reduced colour and COD and Hardness in RO brine:

The existing Activated sludge process based biological treatment along with Decolourant Resin Filter is used to reduce COD and Colour to less than 150 mg/1 and < 700 Pt CO units respectively. The BOD at this stage is less than 10 mg/1. After Biological treatment the treated wastewater is filtered through a Decolourant resin Filter to reduce COD and Colour to less than 100 mg/1 and less than 50 Pt CO units respectively. In order to further improve the COD and Colour and also the Decolourant Resin regenerate volume a 'Hypo Treatment System' has been introduced. This is described in the subsequent section. After decolorizing in Decolourant Filter the Total Hardness is reduced to less than 10 mg/1 using a Weak Acid Cation Resin Softener filter. However, when this treated wastewater is passed through an R.O process, the concentration of COD, Color and Total Hardness is increased the R.O rejects (brine) proportionate to the recovery of water from R.O. Therefore, we need to keep most parameters in the feed to R.0 low in order to ensure the concentration of these parameters is low in the brine and within acceptable levels. Further the ' brine treatment system' further reduces some of the key parameters such as colour in the treated brine.

3.2 Reduction in Decolourant Resin regeneration liquor volume by implementation

Hypochlorite treatment system for reduction of input colour to Decolourant Resin Filter

The effluent from the secondary clarifier with a typical colour of 700 to 1000 Pt Co units will be dosed with sodium hypochlorite in a Hypochlorite contact tank for further reduction of input colour to the Decolourant Resin Filter to less than 100 Pt Co units. Hypo dosing will be controlled by an automated system using online pH. ORP and FRC meters. The residual chlorine will be neutralized by dosing SMBS before feeding into the resin filter. Based on pilot trials conducted at various sites, it is estimated that the frequency of resin regeneration and thereby the Resin regeneration liquor volume and consumption of regenerate chemicals such as Caustic, Salt and Sulphuric Acid will be reduced by 30 to 50%. Reduced frequency of regeneration would also result in increased Resin life.

Before finalising on Hypo treatment, trials were carried out using other colour removal technologies such as Ozonation, Decolourant Polyelectrolyte and Electro oxidation treatment. These systems were found either very expensive (Ozone) or unsuitable for membrane application (Cationic polyelectrolyte). Also no additional benefits such as COD/ BOD reduction etc were seen. Therefore hypochlorite dosing was found most suitable for colour removal. Moreover, hypo did not contaminate the brine, is easy to use, relatively inexpensive and only increased the Chloride content in the brine (which is desirable!).

Key Features/ Benefits of the Hypo treatment system:

■ Addition of hypo in the clarifier outlet and SMBS before Quartz Filter

■ Reduction of colour in the feed to the Resin Filters

■ Increasing Resin Output Between Regeneration (OBR)

■ Reduction in chemical usage for regenerating the resins.

■ Reduction in Resin regenerate liquor volume

■ Increase in resin life from 3 to 6 yrs will be achieved.

3.3 Reduction in SDI ( in the feed to R.O) and Decolourant Resin regeneration liquor volume by implementation of Ultra filtration (UF) Presently, the SDI of the treated effluent after biological treatment and tertiary filtration (Quartz, Decolourant Resin followed by Softener) is > 5. Although, this has not affected the RO membrane performance ( no membrane replacement in any of the 8 CETPs in more than 2 yrs of operation), it is felt that reduction of SDI will reduce Chemical cleaning frequency, permeate blending, membrane flushing, operational downtime and further increase membrane life and system Recovery. For this purpose Pilot trials were done with 4 UF membrane manufactures in 5 CETPs and it was found that SDI of < 3 can be easily achieved.

It was also observed that the performance of the Decolourant Resin Filter improved if UF permeate was used as feed. It was observed that Resin regeneration frequency is reduced by 50% if UF permeate is fed into the Resin Filter thereby reducing the Resin regeneration Volume. This is due to reduction of colloidal material by the UF, as these colloids otherwise gets adsorbed into Resin media. This would mean that the volume of Resin regenerate liquor that needs to be handled in the evaporator system will reduce substantially.

It is observed that with implementation of Hypochlorite treatment system and UF the Decolourant resin regenerate volume reduces to less than 2% from the present 6%.

Key Features/ Benefits of the Ultra filtration system:

• Reduction of SDI to < 3 in the feed to RO.

• Improved Decolourant Resin Filter performance including reduced regeneration frequency & volume.

• Improved Resin Life.

Treatment of Resin & Softener Filters regeneration liquor by Lime - Soda softening Process

In order to improve the possibility for evaporation of the regenerate liquor and improve the possibility of reuse, the Decolourant Resin & Softener regeneration liquor will be separately collected and it will be treated in a Reactor Clarifier with Lime-Soda dosing for softening and polyeleetrolyte dosing for colour removal. Removal of hardness & colour in the BDTRF liquor will make it suitable for feeding into the auxiliary Evaporator or Additional stage R.O Treatment system consists of Reactor clarifier with dosing system to remove hardness from 300 - 350 to less than 100 using lime and soda ash & also reduce colour. Sludge will be dewatered in a separate Filter Press. The sludge can be sent to cement industries. Approx - 0.75 to 1.0 tons/day will be generated. The treated liquor will contain low hardness (<100 mg/1), low COD and Colour but high TDS (20,000 - 25000 mg/1). This liquor can be easily fed to the auxiliary evaporator or better still fed to the proposed additional stage RO to further recover water for reuse. The sludge not only contains Hardness causing agents such as Ca and Mg Salts but also traps COD and Colour. Thus this treatment system serves as an adequate bleed off of these contaminants and prevents accumulation of these by repeated reuse of brine.

Key Features/ Benefits of the Resin & Softener Filter regenerate liquor treatment System:

• Removal of hardness & colour in the BDTRF liquor making it suitable for feeding into Evaporator or Additional stage R.O

• Treatment system consists of Reactor clarifier with dosing system to remove hardness in the combined regenerate liquor (Softener + Decolourant Resin Filters) from 300 - 350 to less than 100 using lime and soda ash & also reduce colour.

• Sludge will be dewatered in a separate Filter Press. The sludge can be sent to cement industries. Approx - 0.75 to 1.0 tons/day will be generated.

• Prevents accumulation and build up of contaminants in the repeated reuse of brine in otherwise closed loop system.

3.4 Reduction in volume of brine using additional stage R.O

The existing RO Plants in the 8 CETP's have either 4 stages or 3 stages. The RO reject TDS in these Plants is in the range of 40000 to 45000 mg/1 for a feed TDS of 6000 - 7000 mg/1. The present RO concentrate volume is in the range of 15 to 17% of feed volume (@ 80 - 85% recovery). Therefore an additional stage of RO (5th stage RO) will reduce the pumping volume of the brine and increase the brine concentration. The additional stage R.O is proposed in all CETPs to increase the R.O brine concentration 55000 mg/1 to 60000 mg/1.

RO brine from additional stage is again concentrated in the MVR-E to get 95-100 gpl cone, the same is being pumped to brine preparation tank. The final brine concentration is 95-100 gpl, therefore dyeing 'dark shades' is easily possible, also for 'medium' and 'light' shades the treated brine can be diluted with water.

Also the treated Resin & Softener regenerate liquor of about 3 % volume, with TDS of 20000 to 25000 mg/1 will also fed into the additional stage R O along with the 4th stage RO rejects (15 - 17% volume). The proposed additional stage R.O system capacity is based on the R.O reject volume of 15% - 17% and treated BDTRF liquor volume of 3% after hypo treatment. This would mean a combined feed of (18 - 20%) to the additional stage RO and final R.O concentrate of 11 - 12%, this can then be fed to the MVR for further brine concentration. 3.5 Increase in Salt concentration and reduction in volume of brine using existing MVR-E.

The volume of brine should be as low as possible so that it is less than the typical dye bath volume of 10% v/v with respect to the total water usage in textile dyeing process. It is with this in mind the additional stage R.O has been installed to reduce the volume to < 12% with 55- 60 gpl concentration. If desired and if required to increase the brine concentration further and in order to further reduce the volume the existing MVR-E is used to further reduce the volume by about 40-50% to bring the brine concentration to range of 95- 100 gpl. This concentration also matches with maximum desired salt concentration in a dye bath for dark coloured fabrics. This reduced brine at 95 - 100 gpl is then further treated in the brine treatment system. Due to the limitation in the MVR (the issue of elevation in boiling point as described earlier) the recovery is limited to a maximum of 95-100 gpl in the MVR Concentrate, which is equivalent to 40-50% recovery in the MVR after installation of the additional stage R.O, since the additional Stage R.O concentrate TDS will be 55 to 60 gpl. Therefore the MVR concentrate volume will be about 6-7%. From this about 5- 7% of the MVR concentrate can be treated in the brine treatment system and pumped to member units for dyeing. Also part of the treated brine (about 0.3%) can also be used for Resin filter regeneration. Only the remaining < 2% of the RO rejects needs to be evaporated in the MEE Type evaporator. The overall plant recovery including permeate and treated liquid brine will be about 97- 98% in the revised process scheme.

3.6 Brine Treatment System:

The brine treatment system comprises of a reaction tank with arrangements for dosing and mixing of chemicals particularly Acid, Sodium Hypochlorite and SMBS for reducing alkalinity, decolorizing and eliminating free chlorine. The colour in the brine is reduced to < 60 Pt Co units (visibly colourless) by this process.

Table - 1: Brief summary of the treated brine quality is given below:

Pumping of liquid treated brine to member units:

The pumping system comprises of a Duplex pump capable of withstanding high chloride corrosion, brine preparation and storage tank, HDPE piping from CETP to member units, flow meter in the main brine line and in the member units along with online data acquisition system.

Key features/benefits of the Brine Treatment System:

1. Pumping the Treated liquid brine with TDS of 95 to 100 gpl (after chemical treatment to reduce hardness & colour) directly to member units through HDPE pipe line.

2. The member units can also switch over to sodium chloride instead of the expensive sodium sulphate as there is no requirement for crystallization and Chloride or Sulphate or mixed salt brine can be used for dyeing.

The brine distribution system can be monitored, similar to the Raw effluent collection and Recovered water distribution system, using flow meters and SCADA arrangement.

3.8 One Specific example of Carrying out the process in accordance with the description with specific parameters falling within above mentioned ranges

Table: 2 Details of Recovered water and Recovered Brine solution

Table: 3 Details of Quantity of Recovered Salt through Brine solution

Table-4 Statement showing the stage wise TDS concentration in the chloride and sulphate based textile effluent

Table: 5 Actual Quality of treated brine:

4. Possible workable substitutes/equivalents/alternatives of materials, substances & process steps that may be used. Other alternative technologies considered for direct reuse of brine - purification using Nano- filtration (NF) System:

Other alternative technologies were considered for purification of the R.O brine. This included the use of Nano-Filtration (NF) system before or after the existing R.O. A detailed analysis indicated two major issues:

i. Use of NF resulted in generation higher volume of reject with higher colour and hardness for evaporation. This would mean further chemical treatment of reject using the lime-soda softening before feeding into the already problematic evaporator. This would also mean higher quantity of waste salt since this would be contaminated with calcium, magnesium (from the hardness in the liquor) and colour making it unfit for reuse, ii. Permeate from the NF had lower TDS resulting in lower salt concentration in the brine discharged to dyeing units. This would mean the dyeing units will need to add more salt making this environmentally unsustainable.

5. The novel & inventive features of the invention which constitute a departure from
the prior art

i. Use of treated brine for textile dyeing without the need for production of crystallized salts from brine using Thermal Evaporators and crystallizers. ii. Production of high quality brine which can be used for textile dyeing without the use of Nano-filtration (NF) system membranes for purification of brine. Avoidance of NF system eliminates the drawbacks associated with it as detailed in section 6 above, iii. Application of the 'brine reuse technology' on a large scale for a CETP which has many member dyeing units unlike an Individual ETP (IETP). iv. Using a combination of Biological treatment, Decolourant Resin filtration, softening resin filters, lime-soda softening of resin filters regenerate liquors and 'brine treatment system', as Technology components, for production of high quality brine which is reused by the dyeing units, v. Reduction in the usage of Thermal Evaporator and Crystallizers for management of R.O rejects thereby reducing dependence on Evaporators for achieving Zero

Discharge in CETPs. vi. Reduction in operating costs for ZLD systems due to reduction in Evaporation and avoidance of the need for crystallization of brine, vii. Demonstration of such technology wherein "treated brine" from Textile dyeing wastewater is reused in textile dyeing in member dyeing units of a CETP . also without the use of Nano-Filtration system for further purification of brine, for the first time in the world.

We claim

1. A process for achieving zero industrial liquid discharge for textiles dyeing wastewater, the brine obtained from the wastewater being treated for re-use in the textile dye baths, said treatment comprising the steps of subjecting the brine to biological processes with decolourant resin filter to reduce COD and colour to less than 150 mg/1 and <700 Pt CO units, respectively: dosing with sodium hypochlorite for further reduction of input colour to the decolourant resin filter to less than 100 Pt CO units; feeding ultrafiltration permeate into the resin filter to reduce the resin regeneration volume: separately collecting the decolourant resin and softener regeneration liquour and dosing with lime-soda for removal of hardness and colour in the BDTRF liquour; reducing the volume of brine with an additional stage RO; and increasing salt concentration and reduction in volume of brine using MVRF-E.

2. A process for achieving zero industrial liquid discharge for textiles dyeing wastewater substantially as herein described with reference to and as illustrated by the Tables.