What is Zero Liquid Discharge (ZLD)?

The term "zero liquid discharge" (ZLD) refers to a treatment process in which the plant discharges no liquid effluent into surface waters, effectively eliminating all environmental pollution associated with treatment. Aside from this advantage, a ZLD process effectively utilizes wastewater treatment, recycling, and reuse, thereby contributing to water conservation through reduced intake of fresh water.

Creating zero discharge solutions is possible by concentrating effluent using various techniques, such as membrane-based and multiple effect evaporation-based systems, as well as water recovery and recycling.

Zero liquid discharge (ZLD) is a strategic wastewater management system that ensures that no industrial wastewater is discharged into the environment. It is accomplished by recycling wastewater and then recovering and reusing it for industrial purposes. As a result, ZLD is a closed loop cycle with no discharge. Although ZLD is an expensive process, it opens the door to economic benefits by recovering salts and other chemical compounds.

The following factors motivate the ZLD system:

· Scarcity of water

· Economics of water

· Environmental laws and regulations

Brackish groundwater desalination to improve water quality and supply

ZLD uses a combination of desalination technologies to produce freshwater while producing zero liquid waste from a desalination plant. This method includes a concentration stage (membrane technologies), as well as stages of evaporation and crystallization (thermal technologies). They produce a pure water stream that can be used for drinking water, irrigation, and other purposes, as well as a compressed solid waste that can be disposed of in an environmentally friendly manner or further processed into a useful material. However, the ZLD method is by far the most expensive and may have an indirect environmental impact due to its high energy requirements. More research is being done in ZLD to reduce energy consumption and incorporate renewable energy sources and low-grade waste heat.

Are ZLD’s implementing ZLD?

Due to strict regulations governing industrial wastewater discharge, many industrial processes are implementing Zero Liquid Discharge (ZLD) systems, primarily for end-of-pipe treatment. A ZLD system primarily entails the use of advanced treatment methods to reduce industrial brine wastewater to dry solids/salts.

When standard wastewater treatment technologies are closely examined, conventional systems frequently result in brine waste near the end of all processing stages. Brine can then be converted into salts/bitterns through additional brine-to-salt processing using ZLD techniques. Some ZLD technologies may result in the recovery of additional water streams as the process progresses.

Conclusion

Since ZLD systems can be integrated into interplant water network systems as either central or distributed units, assessing the presence of both scenarios allows for the identification of cost-optimal designs. Furthermore, any water streams recovered as a result of ZLD processing must be properly accounted for. As a result, this work tries to incorporate ZLD processing options into a previously developed representation for interplant water network design.

All wastewater treatment options have been represented using two distinct stages to facilitate the quantification of brine-to-salt processing:

Stage 1 treatment options result in no brine discharge, whereas,

Stage 2 treatment options result in contamination removal in the form of a brine wastewater stream.

Brine discharge can be reduced by sending brine wastewater streams produced by Stage 2 treatment units for additional ZLD processing.

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