Dr. K Ramesh, Senior Manager (Process Engineering), Tamil Nadu Water Investment Company Limited. Dr. Ramesh can be contacted at email@example.com
Zero Liquid Discharge or ZLD technologies are key to achieving an environmentally sustainable textile dyeing sector. This article explores the path to achieving ZLD, its economic and ecological merits, and the additional support required from governments in driving the change .
The Indian textile industry exports a high volume of garments made of cotton/synthetic materials to foreign countries. As such, the industry makes important revenue contributions to the Indian economy. Particularly in the wet processing of fabric, the manufacturing chain uses a high volume of dyes, chemicals, salts and other auxiliaries to manufacture the dyed fabric. It also uses a substantial volume of fresh water in the wet process for chemical preparation and washing of fabrics. Consequently, these industries produce a great amount of wastewater containing unabsorbed dyes, salts and other chemicals that are extremely toxic. Discharging it without the proper treatment can cause serious harm to the environment. Accordingly, this wastewater must be treated before it is discharged into the environment. The primary and secondary stages of treatment can eliminate the organic pollutants, but can’t eliminate inorganic contaminants. Thus, the government has created a strict environmental standard to safeguard the environment.
In view of the negative environmental impacts caused by the dyeing industry, the pollution regulatory body, Tamil Nadu Pollution Control Board (TNPCB), has directed all industries in the state of Tamil Nadu to implement effluent treatment plants based on zero liquid discharge (ZLD) to prevent the discharge of partially treated/untreated wastewater into nearby water bodies. As directed by the TNPCB, few dyeing industries in Tirupur have established their own captive ZLD facilities, while the other industries have been connected to the CETPs. ZLD is an engineering approach in which wastewater undergoes various stages of treatment and, at the end of the treatment cycle, valuable resources such as clean water and salts are recovered for reuse in the manufacturing process.
Since the ZLD system involves many high-end, sophisticated purification technologies to treat the wastewater and produces valuable resources such as pure water and salt (sodium chloride/sodium sulphate) for reuse in the dyeing process, the capital investment for establishing such treatment plants is substantial.
The initial investment for a captive ZLD system is between $1.8 million and $2 million per million litres per day (MLD) and between $2.6 million and $2.9 million / MLD for a CETP. The recurring cost for maintaining the ZLD-based treatment system in both the cases would be roughly $3/m3 of effluent. Since a dedicated wastewater transmission pipeline is laid to connect the member units to the common treatment facility, to transport the wastewater, the initial capital investment is considerably higher in this case than in the captive plant. However, the operation, maintenance and monitoring of wastewater treatment units is easier in a common treatment facility. Approximately 60%–70% (approximately $2/m3 of effluent) of the recurring ZLD system operating cost could be recovered by producing clean water and salt from the wastewater for reuse.
All the dyeing industries have implemented state-of-the-art wastewater treatment technologies that comprise biological treatment, reverse osmosis (RO) and thermal evaporation technologies to treat toxic wastewater. At the end of the treatment cycle, the valuable resources such as pure water and sodium sulphate salt are recovered from the wastewater and being recycled back for reuse in the dyeing processes. As a result, these industries produce essential resources (sodium sulphate/sodium chloride and pure water) from the wastewater stream, instead of procuring from the open market.
This sustainable practice is helping the dyeing industry in terms of achieving the regulatory environmental standards, while recovering inputs from the wastewater for reuse in the wet processes. As the textile dyeing operation relies on consistent water supply and quality, its operation is sometimes curtailed due to non-availability of water during the dry season. As a result, the entire dyeing operation has to be paused, entailing huge revenue losses for the industry. To overcome this issue and maintain continuous production by the industry, a ZLD-based wastewater treatment facility can be installed to get uninterrupted water supply for dyeing operations and achieve environmental standards at all times.
To boost the textile industry’s growth and achieve an environmentally sustainable production approach, the Ministry of Textiles (MoT), Government of India has announced the Integrated Processing Development Scheme (IPDS) for textile industries to construct common wastewater treatment facilities to which the MSME-based textile wet processing units can be affiliated as a member unit. Under this scheme, the central government will provide 50% of the project cost as a subsidy with a ceiling of INR
.75 crores for ZLD projects, while the state government extends a subsidy at 25% of the project cost. The remaining project cost of 25% (15% and 10% as equity and bank loan respectively) shall be brought by the member dyeing units as an upfront project cost. This scheme facilitates to avail the subsidy only on capital investment of the project and not for any recurring cost of the created facility. However, this scheme is not applicable to establish any captive or individual effluent treatment plant by the dyeing industry on its own.
Some dyeing industries increasingly prefer to create their own treatment plants, owing to some technical issues such as:
Stringent training is required periodically for the operators/professionals of the ZLD facility. Although the government is providing the financial support to establish high-end wastewater treatment technologies, a dedicated technical crew should be deployed to maintain such ZLD facilities. Thus, technical-cum-operational training should be provided to the operators for which the necessary training institutes are essentially to be established with technical experts.