Zero Liquid Discharge (ZLD) refers to a treatment process or system in which factories or treatment plants discharge no liquid effluent into surface waters, in effect completely eliminating the environmental pollution associated with water-intensive production processes.
Pollutants from factories may reach waterways directly through partially filtered or untreated wastewater or they may be deposited into the soil and reach rivers and estuaries through leakage. In these cases, a zero liquid discharge system can solve these problems.
What is Zero Liquid Discharge (ZLD)?
Zero liquid discharge (ZLD) is a strategic wastewater management system that ensures that there will be no discharge of industrial wastewater into the environment.
ZLD is achieved by treating wastewater through water recycling and then recovery and reuse for industrial purpose. Hence it is a cycle of closed loop with no discharge. Although ZLD is a costly process, it paves the way for economic benefits by recovering salts and other chemical compounds.
In developing a zero liquid discharge system, waste water is treated and recycled within the system itself. The treated water is then released into the environment by means of heat and crystallizers. As wastewater treatment costs continue to rise, zero liquid discharge can help companies reduce their water consumption and disposal costs and avoid adverse environmental impacts associated with wastewater discharge.
How To Achieve Zero Liquid Discharge in Wastewater Treatment
Creating zero discharge solutions in wastewater treatment can be accomplished by concentrating the effluent using various techniques, including membrane-based and multiple effect evaporation-based systems, and recovery and recycling of water.
Zero Liquid discharge in wastewater treatment applications can be achieved by combining various technologies, such as:
Thermal processes, like Heat Pump Evaporators
Reverse Osmosis (membrane technology)
Falling Film Brine Concentrators
Horizontal Spray Film Evaporator
Solids Waste Handling
These technologies are key components for brine concentration applications in desalination plants.
What Are the Benefits of Zero Liquid Discharge (ZLD) Plants?
Many are benefits of Zero Liquid Discharge Plants, such as:
Wastewater discharge is avoided by recycling the treated water;
It promotes the sustainability of the industry and the environment at large.
Water recovery reduces resources consumption;
ZLD can cut disposal costs for factories;
Factories reduce their water demand, so more freshwater is available for other purposes;
ZLD helps the environment by stopping water pollution.
The Zero Liquid Discharge process makes effective use of wastewater treatment, recycling, and reuse, thereby contributing to water conservation through reduced intake of fresh water. Also, important resources can be obtained from wastewater, thus making the entire process even more sustainable.
Costs of a Zero Liquid Discharge System or Plant
The costs of a Zero Liquid Discharge (ZLD) system or plant can vary widely, starting from 1,000 up to millions of US dollars.
The costs of such plants are affected by many factors. Firstly, the main costs of a Zero Liquid Discharge (ZLD) system are related to the technology used at the core of the zero-discharge solution. For example, some equipment can be very costly to build, such as multi-effect evaporators, or require costly maintenance, such as Reverse Osmosis systems.
Secondly, the more complex the industrial effluent, the more costly we should expect the system to be. For example, wastewater containing oils, heavy metals, and hard-to-remove colloids, would need a multi-stage treatment system that can greatly increase the costs.
Thirdly, the system flow rate affects the main technology used in these systems and could greatly increase or decrease the price of ZLD systems.
The amalgamation of new technologies with the conventional techniques makes zero liquid discharge systems economical, and efficient, with a cutback in energy consumption.
Importance of Water Chemistry Analysis for Zero Liquid Discharge System
Careful consideration of water chemistry is needed for the successful design and operation of a zero liquid discharge system. In fact, a sound water chemistry design basis is key to successful zero liquid discharge design and technology selection, especially for hard-to-treat wastewaters in factory applications.
Typically, the most relevant chemical constituents of concern for a zero liquid discharge system are:
For all of these components there are dedicated treatment technologies that can be part of the zero liquid discharge solution. For example, calcium and magnesium in water can be removed by softeners to avoid scaling problems, while sulphate in water can be removed using Reverse Osmosis.
Instead, the biological indicator of BOD needs careful considerations since thermal technology could not be the most suitable technique for its reduction.
Zero Liquid Discharge Plants for Industrial Effluents
Each industrial effluent stream presents its own unique challenge when designing an entire Zero Liquid Discharge plant process.
In order to clean water in industrial sectors, a recovery solution needs high quality equipment and careful testing of the chemical properties of the liquid. YASA ET zero liquid discharge plants include desalination, de-oiling, softening, clarification, and filtration for the following processes:
Membrane System Reject (NF, MF, UF, RO)
Cooling Tower Blowdown
Flue Gas Desulfurization (FGD) Blowdown
Integrated Gasification Combined Cycle Gray Water
Refinery, Gas to Liquid, Coal to Chemical Wastewaters
In all of these applications, the zero liquid discharge systems can reduce the wastewater output of factories by 80% on average. The water is recovered as product by separating the contaminants from the waste stream and can be reuse in the production line of factories.
The picture below shows the process flow design for an advanced zero liquid discharge system that features pre-treatment, vacuum evaporators and crystallizers for optimal recovery rate.
An advanced zero liquid discharge system includes vacuum evaporators and crystallizers to reduce the waste disposal and increase the water recovery rate of the process. Usually, for desalination plants, this kind of system includes thermal treatment followed by brine concentrators or dryers.
What Is the Best Technology for Zero Liquid Discharge?
The best treatment technology for zero liquid discharge projects always relies on various treatment stages and processes. The correct set of equipment needs to be selected and carefully designed to reach the optimal ZLD results.
The first step in designing a zero liquid discharge treatment system is to analyze the chemical composition of the industrial effluent to be reduced. Secondly, extensive testing needs to be undertaken to find the correct parameters for treating the specific wastewater. Finally, the best technology for the treatment system can be picked and the system can be installed at the client site.
For the right treatment system, you need the right expertise.
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