Electrodeionisation (EDI)

The route to ultrapure water without chemicals

Electrodeionisation is an advanced membrane technology that combines electric current, ion exchange resins and selective membranes to purify water to an extremely low conductivity. Whereas reverse osmosis removes the bulk of the salts, EDI acts as the ultimate polishing step for processes that require total demineralisation. The biggest advantage? A continuous process that regenerates itself electrically, without the use of acids or caustics.

What is EDI?

What is electrodeionisation and how does it work?

In electrodeionisation, charged particles (ions) are removed from the water under the influence of an electric field. Unlike conventional ion exchangers, in which the resins become saturated and have to be regenerated chemically, an EDI unit operates continuously and autonomously.

The electric field as the driving force

By applying a potential difference across the EDI stack, cations are drawn towards the cathode and anions towards the anode.

Ion-selective membranes

Special membranes only allow ions with the right charge to pass through. This creates a pure product stream (diluate) and a concentrated waste stream (concentrate).

Continuously self-regenerating

The electric current splits water into H⁺ and OH^- ions. These ensure that the ion exchange resin in the unit is continuously regenerated, so downtime for regeneration is a thing of the past.

Polishing after RO

An EDI unit is almost always installed downstream of reverse osmosis (RO). The RO removes >98% of the salts, after which the EDI removes the remaining ions to achieve a conductivity of < 0.1 µS/cm.

Why choose an EDI installation from PCA?

For companies striving for water quality of the highest standard, EDI offers a reliable and environmentally friendly alternative to the conventional mixed-bed ion exchanger.

Operational & technical benefits

Consistent ultrapure quality

Unlike batch processes (such as resins that become exhausted), EDI delivers an uninterrupted flow of water with a stable, extremely low conductivity.

No chemical handling

Because regeneration takes place electrically, there is no need to store or handle aggressive chemicals such as hydrochloric acid or caustic soda. This significantly improves safety in the workplace.

Compact footprint

EDI systems are modular and take up considerably less space than traditional ion exchange columns with their associated dosing installations.

Economic & sustainable gains

Lower operating costs (OPEX)

With no chemical regeneration and no associated neutralisation of waste water, the operating costs per m³ of water produced are very favourable.

Minimal maintenance

The system has no moving parts and, provided the pretreatment (RO) is correct, requires very little intervention.

Focus on total demineralisation

Where necessary, we use EDI for complete desalination, but we also advise on selective removal if your process-specific parameters allow it.

Tailored configurations: from design to build

PCA Water designs EDI installations that integrate seamlessly into your existing or new water management system.

Production of ultrapure water

EDI removes the remaining dissolved ions after pretreatment, such as reverse osmosis, making it possible to produce water with a very low conductivity and high resistivity.

Selective ion removal

Depending on your influent (e.g. specifically for silica removal), we optimise the settings of the EDI stack to meet your exact standards.

Hybrid systems

We combine RO and EDI in a single skid-mounted installation, fully automated and monitored for conductivity, pressure and current.

In which sectors is electrodeionisation indispensable?

Wherever 'ordinary' demineralised water is not pure enough, EDI provides the solution.

Microelectronics

Chip manufacturing requires ultrapure water (UPW) with a conductivity approaching the theoretical limit of pure water.

Pharmaceutical industry

For the production of Purified Water (PW) that meets the strictest pharmacopoeia requirements.

Surface treatment

For rinse baths in high-end coating processes, where even the slightest ionic contamination can affect adhesion.

Energy & steam generation

Essential for boiler feed water in high-pressure boilers to prevent corrosion and deposits on turbine blades.

FAQ: frequently asked questions about electrodeionisation

Is RO pre-treatment always required?

No. An EDI module requires feed water with very low hardness and salt load to prevent scaling in the stack. Reverse osmosis (RO) is usually used for this, but a suitable ion exchanger can also be used as pre-treatment.

What is the difference between EDI and a mixed-bed ion exchanger?

Both EDI and a mixed-bed ion exchanger are used for advanced demineralisation of water. A mixed bed uses a mixture of cation and anion resins that must be chemically regenerated once saturated, whereas EDI removes ions continuously and regenerates the resins electrically. This allows EDI to operate continuously with lower chemical consumption.

How long does an EDI module last?

With correct pre-treatment and monitoring of process parameters, EDI stacks have a service life of 7 to 10 years.

Experience the difference with PCA Water.

Would you like to know whether electrodeionisation can help you? Get in touch with us.

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