Zero liquid discharge (ZLD) technology

What is zero liquid discharge

ZLD - the advanced water treatment process

Zero Liquid Discharge (ZLD) is an advanced water treatment process with the goal of reusing as much water as possible in the production process without the need to discharge any waste.

ZLD is the ultimate wastewater treatment process that has zero or nearly zero impact on the environment. By combining several processes, salt (which can be reused or sold) and purified water that can be reused in the technology, are recovered from the wastewater. This makes it possible to reduce the operating costs of the main technology. These benefits make ZLD one of the most popular technologies to reduce the industry's environmental impact, especially in countries that are subject to strict environmental regulations on industrial waste.

Zero liquid discharge system

ZLD process typically involves the following steps: pretreatment, concentration and thermal treatment.

Pretreatment is used to reduce the amount of TSS (Total Suspended Solids), COD (Chemical Oxygen Demand) and turbidity. After removal or significant reduction of TSS, COD and turbidity of treated wastewater, other wastewater treatment processes can be used

Concentration of dissolved solids in the ZLD system is usually accomplished by membrane technologies, such as reverse osmosis (RO), electrodialysis (ED) or by a combination of RO with ED. With the help of ED technology or the above-mentioned combination of RO + ED, we can achieve recovery of more than 98 % of treated water.

Thermal treatment - the last step of the ZLD process is usually consisting of evaporator and crystallizer. The output of this process are crystalline salts NaCl, Na₂SO₄, etc. These salts can be sold for further processing. Any unusable solid waste is landfilled at controlled landfills. Evaporated water can be reused as condensate.

MEGA Electrodialysis zero liquid discharge plant

Benefits of ZLD plant

Zero liquid discharge plant technology is growing globally as an important wastewater management strategy to reduce water pollution and extend water supply. The main benefits of ZLD are:

Minimizes wastewater discharge.
Maximizes water recovery.
Creates a valuable product for sale and further processing.
Removes many environmental issues.
Reduces dependence on local water sources.
Significantly reduces the risk of sanctions within the legislative standards for discharged waste.

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ZLD system by MEGA

RALEX® ED(R)-IF – The world's most capable electrodialysers

The electrodialysis stacks ED(R) - IF/250 and 400 developed by MEGA focuses mainly on increasing the concentration of dissolved salts in wastewater. Thanks to this product, we offer the possibility to significantly reduce the amount of waste stream entering the so-called ZLD thermal stage. Due to the smaller volume of treated wastewater, we significantly reduce the overall operating costs of the wastewater treatment technology.

We are also capable to offer technology for ZLD plant without the thermal treatment using a special type of electrodialysis with bipolar membranes (EDBM, BPED). This technology can utilize the contained salts to produce acid and caustic that can be locally used in further production. Such technology then has three outputs – acid, caustic and desalinated water which meets the local legislative standards for discharges.

Thanks to the experience we gained since the 1980s in the field of industrial electrodialysis technology, we were able to develop new generation stacks. The developed ED(R) - IF electrodialization stack is the most efficient membrane concentrator used in ZLD processes.

RALEX membranes for different industries and processes

Industrial use of ZLD technology from MEGA

Today, MEGA offers its electrodialysis units for installation in ZLD technologies around the world. The main application of our technology is in:

Textile industry,
power industry,
tanneries,
breweries,
chemical industry,
petrochemical industry,
paper industry,

and many other industries all over the world.

Advantages of MEGA electrodialysis in ZLD processes

Lower pretreatment requirements – higher TSS, COD and turbidity limits in the feed water.
High concentration of salts in the waste stream (up to 200 g/l).
Possibility to avoid evaporator with direct use of crystallizer.
The silica content in the feed does not affect the degree of salinity and water recovery of the entire system.
Significant reduction in capital and operating expenses.
Low chemical demands.
Operation under low pressure.
Standard parts replacement frequency.

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RO brine treatment

Increasing the capacity of existing RO technology can be achieved by combining RO and ED (R) technologies. Even that the working principles of these two technologies are far from each other, we are proud to own the know-how of coupling these together in industrial scale and to provide this solution to the customer.

Advantages of RO brine treatment by MEGA ZLD system

Increases water recovery of existing RO technology.
Increases capacity of an existing plant without further wastewater treatment.
Increases recovery of SWRO without the need for marine works.

Our ZLD projects

Zero Liquid Discharge Water Treatment EDR

ZSNP at Žiar nad Hronom, Slovakia

ZLD (feed and bleed mode) for desalination of tailing ponds after production of aluminium oxide

Leading Slovak producer of aluminium, ZSNP, produces a large amount of sludge, which is deposited in a tailing pond. The wastewater from this tailing pond is strongly saline with a high pH, therefore, it cannot be discharged into the river. In this case, MEGA used the experience of previous projects and designed a zero liquid discharge system that is based on the so-called FEED and BLEED mode. Thanks to this ZLD technology we were able to ensure continuous quality of both the desalinated stream (6 g/l) and the concentrate stream (180 g/l), which is subsequently processed in the evaporator.