ZLD technologies consist traditionally from brine concentrators and crystallizers that use thermal evaporation to turn the brine into highly purified water and solid dry product ready for landfill disposal or for salt recovery. While evaporator/crystallizer systems are the most commonly used in ZLD processes, other promising technologies (ED/EDR, FO and MD which will be explained later) with high recoveries have taken foothold and are used in different combinations in order to lower the cost and raise the efficiency of the systems.
The increasingly tighter government regulations on the discharge of brine due to the environmental effect make ZLD necessary when water is scarce or the local water bodies are protected by law. Thus many industrial facilities and brine effluent contributors that up to now where either discharging brine to nearby available surface water or the sea and to wastewater treatment plants, are trying to find new ways to tackle this issue.
The industrial involvement with brine is twofold. Many industrial processes require water which they contaminate and releasing it may cause irreversible damages to the local environment.
In India and during the last decade due to heavy contamination of local waters by industrial wastewater was followed by strict regulations that make ZLD necessary in order to ensure the future of their rivers and lakes. In Europe and North America, the drive towards zero ZLD has been applied due to the high costs of wastewater disposal at inland facilities. These costs increase exponentially by government fines and the costs of disposal technologies.
ZLD can also be used to recover valuable resources from the wastewater which can be sold or reused in the industrial process. Some examples are as follows,
- Generation of valuable potassium sulfate (K2SO4) fertilizer from a salt mine
- Concentration of caustic soda (NaOH) to 50 and 99% purity
- Recovery of pure, saleable sodium sulfate (NaSO4) from a battery manufacturing facility
- Reduction of coal mine wastewater treatment costs by recovering pure sodium chloride (NaCl) which can be sold as road salt
- Lithium (Li) has been found in Indian oil field brines at almost the same level as South American salars
- Gypsum (CaSO4.2H2O) can be recovered from mine water and flue gas desalinization (FGD) wastewater, which can then be sold to use in drywall manufacturing
Other advantages to the application of ZLD are:
- Decreased volume of wastewater lowers the costs of waste management.
- Recycling water on site thus decreasing the need for water intake and meeting with treatment needs.
- Reduce the truck transportation costs for off-site disposal and the related environmental risks.