Zero Liquid Discharge (ZLD) Systems: Design Considerations and Importance of Water Quality Monitoring

 Zero Liquid Discharge (ZLD) Systems: Design Considerations and Importance of Water Quality Monitoring

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Resource Recovery and Waste Reduction through Zero Liquid Discharge (ZLD) Systems

A zero liquid discharge (ZLD) system is a process that reduces industrial waste generation while recovering resources that are present in wastewater. These resources can include carbon, water, nutrients, heavy metals and energy. WATERMAN ENGINEERS AUSTRALIA

A ZLD system typically uses a combination of pre-treatment, concentration and evaporation to produce a solid product suitable for disposal. The first step is usually a reverse osmosis (RO) process to concentrate dissolved substances. This method also allows the production of ultrapure water.

The next step in ZLD treatment is to evaporate the waste liquids. This can be done with thermal processes or a high-pressure distillation unit to produce a solid product. The resulting water vapor can then be recycled into the plant or a solid waste can be produced that is suitable for landfill.

Some power plants produce waste liquids that contain salts, such as those from wet gas scrubbing, coal pile run-off or leachate from gypsum stacks. These waste products can be vaporized in a modern ZLD system to create clean water that can be used in the plant or reused for another industrial application, such as a sewage treatment plant.

These wastewaters often contain small amounts of regulated inorganic contaminants such as heavy metals, boron, and selenium that require a treatment step to remove before discharge. One option for treating these wastes is to use a membrane system to pre-concentrate the waste water before evaporation. This process can significantly reduce the size of backend evaporation equipment and minimize capital and operating costs.

Depending on the specific composition of the waste water, this can be accomplished with softening, pH adjustment or another appropriate pre-treatment. This can reduce the number of Total Suspended Solids (TSS) and extend the life of the membrane.

Another option for treating these types of wastes is to utilize a chemisorption process. This process enables the removal of soluble compounds from wastewater using activated carbon.

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