By Ravichandran Selvaraj

Industries across India in their endeavor to meet regulatory norms, sustainability objectives and corporate governance goals are beginning to explore and adopt Zero Liquid Discharge (ZLD) standards at their treatment plants and no longer consider wastewater treatment a liability but a key resource recovery system.

Currently, in India, water use efficiency – a ratio of water withdrawal to discharge volumes, is not monitored in industries but with growing consumer pressure for freshwater and scarcity issues, water as a resource simply cannot be used once in the manufacturing processes and discharged.

By leveraging the principle of a circular economy, Zero Liquid Discharge aims to close critical water loops and foster reuse over continuous cycles through extended treatment.

ZLD IMPLEMENTATION

At present, industrial sectors including Textile, Pharma, Pulp and Paper, Chlor-alkali, Sugar, Power, Dye and Dye-intermediates, Petrochemicals, Steel, and Fertilizer have implemented ZLD based on mandates from state pollution control boards.

Currently, ZLD implementation in the country comes from judicial orders and statutory mandates from state pollution control boards based on factors such as:

• Classification of the industry – Grossly Polluting Industry (GPI)
• Water consumption and discharge rates at the industry
• Auxiliary chemical usage in the manufacturing process
• Challenge in the conveyance of treated effluent for discharge
• Impact on the immediate environment due to discharge
• Water scarcity issues in the immediate environment

Thus, as India grips with water security issues, ZLD is rapidly becoming a norm for industries to address through regulatory statutes and drive to reuse treated wastewater.

Figure 2

REJECT MANAGEMENT SYSTEMS

Of the several factors to consider while installing a ZLD system at a facility, one performance parameter standing tall in CAPEX and OPEX considerations is Brine Reject Management.

Brine management of effluent takes up close to 50% in CAPEX of any potential ZLD project. Thus, an evaporator system addressing brine management can make or break the operations. Additionally, reject management systems also weigh heavily in OPEX due to dependence on the constant running of utilities such as power and steam.

Moreover, the evaporators currently available in the market rely on dated legacy solutions and complex system architecture.

Gradiant’s Carrier Gas Extraction (CGE) system is proprietary humidification and dehumidification (HDH) based thermal evaporator system that incorporates carrier gas to cause a phase change of feed water from liquid to vapor. The CGE system reimagines the conventional evaporator based on product innovation to suit a wide range of industries. Some of the key benefits that a CGE system possesses that sets it apart from legacy evaporators are:

• The direct phase change from liquid to vapor unlike conventional systems
• Operates at ambient pressure instead of vacuum pressure
• Ease in overcoming scaling issues without major stoppages of the plant

The advantages and leap in operating philosophy of the CGE system are made possible by mimicking the humidification and de-humidification operations of the natural rain cycle. Additionally, this principle is translated to an industrial scale process with the help of novel bubble column architecture ensuring minimal rotating parts and an easy-to-operate system.

Figure 3

CASE STUDY

A prominent textile processing firm in Tirupur, Tamil Nadu (the textile processing capital of India), while looking for an innovative and comprehensive ZLD solution, engaged with Gradiant to procure a Carrier Gas Extraction (CGE) based system to alleviate their challenging effluent handling needs. The project showcased is the country’s first CGE based ZLD system that is commercially scaled and operated successfully for over a year.

Gradiant designed a system comprising of the CGE, crystallizer, pusher centrifuge, and an agitated thin film dryer to effectively handle 200 m3/day of textile processing effluent with a feed TDS of 55,000 ppm. Furthermore, the scope of the project includes the design, engineering, construction, erection, and commissioning along with operation & maintenance of the ZLD system.

At the outlet of the treatment train, the system recovers freshwater of TDS less than 50 ppm, hardness less than 50 ppm, pH between 6 – 6.5, colorless than 100 on the platinum cobalt scale. Additionally, close to 1.2 tons of salt is recovered per day. The Glauber’s salt recovered is reused by the dyeing process of the textile mill.

HOW DOES IT WORK?

While achieving performance metrics of salt concentration and freshwater recovery in comparison to other legacy evaporator systems, the CGE, with the difference in operation ensures minimal maintenance and downtimes.

With the placement of a heat exchanger outside the main installation, the CGE system minimizes scaling inside CGE towers, overcoming scaling issues while maintaining efficiency and extending the minimal cleaning cycles. A single-pass via the CGE system, as shown in Figure 3 and 4, would constitute the feed wastewater entering via the heat exchanger which then is passed over to the humidifier column, where carrier gas, usually ambient air, is introduced into the system through an air blower. Due to the gradient in concentration and temperature, the air is heated and transfers freshwater as a vapor to the de-humidifier column with concentrated waste being phased out of the system.

With the passage of humid air through the proprietary multistage bubble column and the exposure to cycled cool water, freshwater is recovered, and heat supplied is also recovered.

This phase change of feed water from liquid to vapor including the recovery of freshwater happens seamlessly. Moreover, there is a decoupling of the surface of heat transfer and phase change from liquid to vapor. This results in increased efficiency of the overall system as typically scaling largely occurs in evaporators due to heat transfer. With the decoupling in the CGE system, Cleaning-in-Place (CIP) protocols are greatly reduced.

These benefits when translated to site conditions result in maximum uptime for the CGE system. In contrast to legacy systems, the heat exchanger (twice a month) and humidifiers (once a month) can be easily cleaned. Additionally, the cumbersome process of hydro jetting-based cleaning is not required due to the innate differences in the operation of the CGE in overcoming scaling.

In conclusion, as ZLD norms are getting notified by more statutory bodies across the country for varying industries, there is a requisite of benchmarking currently available technologies to address the normative needs of end-user for economic operation and passed on benefits of ZLD to the environment. The CGE system developed by Gradiant provides avenues as a technology disruptor in this niche space of wastewater treatment with proven commercial scaling in India and abroad.

This case study was published in the annual “Finest-50 Global Case Studies” Special Digital Edition, March-April 2022. Click here to read the complete e-Magazine issue.

About the Author

Ravichandran Selvaraj is the Managing Director of Gradiant India (P) Ltd. He has over 30 years of experience in the water and wastewater industry. Prior to Gradiant, he worked at various multinational organizations such as Nalco, Ecolab, Praj Industries, and Ion Exchange. He has built a 50-member strong team that backs him.
Gradiant has its Indian headquarters in Chennai, with capabilities in Design, Research, Process, Engineering, Project Execution, and O&M. Operations is supported by an in-house lab facility. The sales and marketing team operates from Chennai, Coimbatore, Pune, and New Delhi.

This case study was published in the annual “Finest-50 Global Case Studies” Special Digital Edition, March-April 2022. Click here to read the complete e-Magazine issue.

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