Electrodialysis desalination

Types of Electrodialysis Desalination

As mentioned previously, electrodialysis desalination is the process of using electricity to separate salts from water by passing it through selective ion-exchanging membranes. This method works better on water with low to medium total dissolved solids (TDS) and is cost-effective for treating brackish water. Electrodialysis functions with various ED stacks that are useful for different water qualities and quantities.

• Electrodialysis (ED)

  The electrodialysis apparatus primarily comprises an assembly of cation-exchange membranes, anion-exchange membranes, and feed spacers. It is suitable for the direct desalination of seawater to produce drinking water. However, for feed solution with a low initial pH, the configuration of the ED stack should comprise an anode, a cathode, and CCM as well. Besides ED for seawater desalination, it can also be used for seawater concentration, for example, in salt recovery plants; therefore, there could also be a variant of the assembly for that purpose only.

• Electrodialysis Reversal (EDR)

  An electrodialysis reversal device consists of a repeating sequence of cation-exchange and anion-exchange membranes separated by diluting and concentrating channels. It is suitable for the desalination of water with a higher quantity of salt than the ED. Furthermore, because the current flow direction is reversed after some time, precipitation, scaling, and fouling of the membranes can be avoided.

• Continuous Electrodialysis (CED)

  Unlike conventional electrodialysis that works in batch mode, continuous electrodialysis operates in a continuous flow manner, which results in a constant product stream, high recovery rate, and low operation cost. This mechanism also leads to low capital costs and smaller facilities for further treatment.

• Capacitive Deionization (CDI)

  The basic concept of CDI is to perform electrical double layer charging and discharging cycles to adsorb ions from water to remove them. Therefore, this device behaves like a capacitor. Like EDR, CDI works better on water with low to medium total dissolved solids (TDS) and is cost-effective for treating brackish water as well. However, CDI and EDR work separately. Therefore, CDI can be used for preliminary water treatment to remove the fouling material before further treatment in the EDR device.

Specifications and maintenance of electrodialysis desalination

• Flow rate: Electrodialysis stacks are designed to process specific feed water flow rates. A typical small-scale ED stack may treat 1 to 5 m3/h of seawater or brackish water, while larger industrial systems can handle 20 m3/h or more. Sizing the stack for the desired flow rate is crucial to achieving the target desalination capacity.
• Consumption: Electrodialysis desalination plants require electrical power to drive the electrochemical process. The power consumption depends on the feed water salinity, the desalination efficiency of the ED technology used, and the amount of water treated. Proper stack design and optimal operating parameters can minimize power consumption and operating costs.
• Membrane materials: The cation and anion exchange membranes used in electrodialysis units are typically made from polymeric materials. The specific composition and structure of these membranes vary by manufacturer to provide the desired ionic conductivity and separation characteristics. Regular membrane integrity inspections are essential, which include visual assessments, checks for typical leakage points, and measuring electrical resistance to ensure they are still functioning as designed.
• System components: Electrodialysis systems have multiple parts, including feed pumps, pressure vessels, ED stacks, conductivity meters, and more. Each component has its maintenance needs. Routine checks should be done on different equipment parts to ensure a proper operating process. Follow the maintenance guidelines provided with the equipment for the best results and a longer service life.

Scenarios of Electrodialysis Desalination

Industries and scientific research leverage the benefits of ion-exchange membrane electrodialysis ED for desalination, as they have many uses and advantages.

• Production of Fresh Water: The main use of ED desalination is to separate salty input streams, like seawater or brackish water, to produce fresh water that can be used for drinking, irrigation, or industrial purposes.
• Water Scarcity Solutions: In regions facing water scarcity, electrodialysis ED can provide an alternative source of fresh water by treating saline water sources.
• Aquaculture Water Treatment: Aquaculture industry employs ED desalination to reduce the salinity of seawater for fish and shrimp farming, thus providing a suitable living environment for aquatic organisms.
• Industrial Water Supply: Industries such as power generation, petrochemicals, and electronics require an adequate supply of fresh water for cooling, manufacturing, and cleaning. ED desalination can be used to provide a stable source of fresh water to meet these industrial water needs.
• Landfill Leachate Treatment: Landfill leachate has high salinity; using electrodialysis as part of a treatment process can reduce the salinity for safe discharge or further treatment.
• Desalination in Closed-loop Systems: Closed-loop systems such as cooling towers and recirculating aquaculture systems can use ED desalination to maintain water quality and prevent the buildup of salts.
• Marine Energy Extraction: Electrodialysis ED can be used in osmotic pressure power generation and salinity gradient energy extraction, which converts the energy produced by the salinity difference into electricity. This is a new way to produce renewable energy.

How to choose electrodialysis desalination machines

Business buyers looking to acquire the ED for industrial applications can purchase the following types from suppliers:

• Laboratory Electrodialysis Units

  They have modular designs that enable customizable configurations depending on research needs.

  Opt for units with adjustable current density and ionic permselectivity for varying sample characteristics.

• Industrial Electrodialysis Units

  Focus on capacity, modular design, and separation efficiency when choosing industrial plants. Electrodialysis stacks with larger membrane surface areas are ideal for high-volume processing.

  Purchase units with automated control and monitoring systems for unattended operation in a central production facility.

• Electrodialysis for Concentrate Treatment

  These units are available to buyers so they can offer customers options for recovering valuable components from waste streams.

  Choose systems that have membrane materials capable of withstanding fouling by specific feed streams to ensure a longer operating life.

• Modular Electrodialysis Systems

  Request for modular ED systems with flexible configurations suited for different applications. Make sure the modules support quick membrane replacement and flexible electrode arrangements.

• Portable Electrodialysis Systems

  Consider portable electrolysis devices for on-site processing in remote locations. These compact models should have rugged construction for field deployment and obstacle resistance.

• Electrodialysis for Water Purification

  Select the appropriate pre-treatment and post-treatment coupling systems to ensure comprehensive water treatment.

Electrodialysis desalination FAQ

Q1: Is ED desalination more effective than other methods?

A1: Electrodialysis desalination has its advantages. It is more effective when dealing with high salt content in water. Furthermore, the energy consumption of electrodialysis desalination decreases as the salt content in the water increases, making it a preferable choice for brackish water and high saline water sources.

Q2: What is the lifespan of electrodialysis ED modules?

A2: Typically, the modules can last for over ten years, provided they are well maintained and operated within the recommended parameters.

Q3: Can electrodialysis ED be used for seawater desalination?

A3: While it's technically feasible to use electrodialysis for seawater desalination, the high salt content in seawater would make the energy consumption greater, resulting in a less economical choice when compared to other available desalination techniques like electrodialysis reversal (EDR) and multicrystaline salt extraction.