Zero Liquid Discharge - Cold process
With Salt Repellent Technique

The world is facing an acute water crisis. Desalination of seawater is essential, but current methods, like distillation and reverse osmosis, create more pollution. High saline wastewaters from industries pose an additional problem. The Salt Repellent Technique offers a revolutionary solution. (For simplicity, the term ‘seawater’ denotes all types of saline waters including RO, nano, and super saline and borated wastewaters).

2. Why Repellents?

When seawater freezes, ice forms, but salt gets trapped inside. Traditional methods to wash away this salt are not cost-effective. We use special substances called repellents. In small amounts These repellents force the salts away from water molecules, creating pure ice.

The Desal process is explained by these simplified steps:

1. Water is the solvent for all the salts in seawater. (Seawater contains 3% NaCl and 0.6% other salts).
2. In Ethanol, the repellent, most of the salts are sparingly soluble. (Solubility of NaCl in water: 36% and in EtOH: 0.06% only, almost insoluble).
3. Water and ethanol are easily miscible and give a clear solution.
4. By freezing the water to ice at -4o C, only the water part turns into ice. (The presence of ethanol in water acts as a barrier / shield preventing the salt from getting trapped in the ice crystals as they form. This gives us clean, salt-free ice! (It is similar to mosquito repellent, preventing mosquitoes to come nearer to human bodies. The earlier attempts of scientists failed because they did not use this barrier, consequently, NaCl got trapped inside the ice crystal cage, just as insects get trapped in mangoes and fruits)
5. The salts get squeezed into remaining water that did not freeze, making it extra salty.
   
6. The ice- brine slurry is centrifuged to get desalted ice which on warming, gives desalted water.

3. Process For Freeze Desalination of Seawater Using Repellents

Seawater is filtered to remove solid impurities, mixed with repellents, cooled to -4°C, to get salt-free ice slurry. It is centrifuged to get ice crystals and on warming pure potable water is obtained. The desalting step is repeated on the leftover brine to get more clean water and a higher yield of desalted water. A flowsheet is given below:

4. Desalination of RO, Nano And Super Saline Waste Waters

Sea water in many Gulf countries as well as the retentates of RO and industrial plants contain higher dosages of salts and cannot be used for drinking or recycle in industries and are let out without sufficient treatment.
To reduce such pollution problems, experiments were carried out with artificial seawater having a TDS of about 70,000 ppm, mixed with repellents and cooled when ice crystals started to form. Due to the presence of repellents in water, all the salts are driven away from ice crystals and the resulting ice is free of salts, which on warming produces desalted water. Thus, High salt brine was desalted from 69,820 ppm to 240 ppm in three stages of desalination, as shown in Fig.1

(Tables are important to see results fast. Pl. format it as given below)

Table 1:  Test Results of Desalination of High Salt Brines (Figs. In mg/L)

4.4.1 Boron Removal

Although boron is essential for plant growth, high concentrations in the soil can damage sensitive crops and disturb in human reproductive systems and removal of boron from water has become a necessity. The Freeze desalination experiments conducted with IS repellents reduced the Boron level from 2.3 mg/L to a remarkably low level of 0.02 mg/L which is well below the requirements set by WHO. The results are given in Table 1 above.

Similarly, IS Repellents provide a speedy method for recovering lithium chloride from Li-brines by reducing overburdened water economically, (unlike the slower solar evaporation process), resulting in crude Lithium salts, to get battery-grade lithium.

Zero Liquid Discharge – (Cold Process) for Polluted Industrial Waters

At present, desalting of brine is done by MLD (Minimum Liquid Discharge) or ZLD (Zero Liquid Discharge) process. MLD achieves 85% water recovery, and considered more cost-effective than ZLD due to lower energy needs. ZLD reaches 95% water recovery, ensuring near-total elimination of wastewater.

Both ZLD and MLD technologies use reverse osmosis, evaporation and crystallization to reduce TDS. Evaporation in multi-effect evaporators is common in both processes and involves high energy costs (100-300 kWh per cu.m. of water treated).

To reduce high energy cost, for the First time freeze desalting with ion-specific (IS) repellent mixtures has been developed with

promising results. This Cold ZLD process recovers additional water and salts at lower temperatures, reducing cost and environmental impact.

The concentrated brine from the centrifuge was further desalted, with two additional stages to get desalted ice with lesser TDS values. The ice samples from different stages were consolidated and subjected to desalination once again, resulting in purified ice/ water with a TDS of about 415 ppm. The super-concentrated remaining brine was evaporated under the sun for two days to get dry salt. The process flowsheet is the same as in Fig 1 above. The experimental results are given below:

Desalination of Polluted Industrial Waters (Fig. in ppm)

The results indicate a significant reduction in TDS value from 38,860 ppm to 415 ppm, COD from 1,558 ppm to below quantifiable limit (BQL), and Boron from 2.36 ppm to 0.38 ppm. Moreover, the removal of the effluent’s yellowish colour renders the water stream suitable for reuse. Analysis of the ZLD precipitate reveals the accumulation of all pollutants, which can be utilized for the recovery of valuable chemicals.

Thus, for the First time, an innovative Cold Zero Liquid Discharge (Cold ZLD) system has been developed for treating polluted industrial waters, to reduce pollution and cost. This novel Cold ZLD technology eliminates the need for pre-treatment, regardless of the salinity percentage of salts in the brine, resulting in lower power consumption, simplified operations, and reduced corrosive impact on equipment.

6. Advantages of Repellent Technique, over RO Process:

• Summary: Even with uncertainty, the Repellent Process promises potential savings on energy, pre-treatment, and pollution.

6.1 RO vs Repellent process

The choice between RO and freeze desalination depends on the salinity level of the brine. RO is said to be more energy-efficient and is therefore recommended for desalination of less concentrated brines such as the desalination of seawater. On the other hand, freeze desalination is recommended for treating highly concentrated brines, including retentates of RO processes and highly polluted industrial waters.

Although boron is essential for plant growth, high concentrations in the soil can damage sensitive crops and disturb in human reproductive systems and removal of boron from water has become a necessity. The Freeze desalination experiments conducted with IS repellents reduced the Boron level from 2.3 mg/L to a remarkably low level of 0.02 mg/L which is well below the requirements set by WHO. The results are given in Table 1 above.

Similarly, IS Repellents provide a speedy method for recovering lithium chloride from Li-brines by reducing overburdened water economically, (unlike the slower solar evaporation process), resulting in crude Lithium salts, to get battery-grade lithium

Cost of desalination

The operating cost of desalting depends mainly on the salinity of feed water. Pilot studies are needed to determine precise energy consumption under various conditions. For a 10 million gallons/ day Freeze Desalination of RO water, the energy consumption is estimated at 4.5 to 15 kwh/ m3. Considering pollution abatment and various other advantages listed above, freeze desalination holds promise as an alternative process for desalting saline waters.

To offset the high operating costs, brine mining is foreseen which facilitates to recover high-purity chloride, bromide and iodide salts, all of which are in great demand. Thus, setting up an integrated Desalination plant with a downstream brine mining unit will result in zero cost for water, less pollution and recovery of valuable chemicals.

We hold patents of our findings, as approved by US, India, and PCT authorities. Based on the above, we offer details of the patents under two headings, namely,

1. One time Patent Licensing Fees (Collected by selling KnowHow reports) and
2. Recurring Royalty fees, (payable annually, based on the value of water recovered)

The cost will be worked out as per the discussion with clients.

we invite MNCs, EPC firms, patent attorneys, agents, and institutions to partner with us so that we together, deploy this transformational technology and create a world where clean water is accessible to all.

Disclaimer:  We provide comprehensive process know-how based on our extensive research and development. For optimal results and to tailor the technology to specific site conditions, we strongly recommend licensees partner with qualified project consultants. While we offer detailed guidance, ultimate project success depends on factors including proper implementation, integration with existing systems, and local regulations.