Standard Operating Procedures For Startup, Shutdown And Stable Operation Of EDI Water Treatment System

In the field of ultrapure water production, EDI technology has become an important part of high-purity water production in industries such as electronics, pharmaceuticals, power generation, and chemicals. Especially in boiler feed water and industrial ultrapure water systems, the EDI Water Treatment System is widely applied in high-purity water production systems due to its advantages of no acid or alkali regeneration, high automation level, and stable water quality output.

However, many enterprises have found during actual operation that problems such as decreased product water resistivity, increased module pressure differential, and shortened module service life are often not caused by the quality of the EDI equipment itself, but rather by improper startup and shutdown operations or insufficient operation management.

For an EDI water treatment system, proper startup, shutdown, and stable operation procedures not only determine the quality of produced water but also directly affect the operating cost of the system and the service life of the equipment.

Why Are Standardized Startup and Shutdown Procedures So Important for EDI Systems?

EDI modules integrate ion exchange resin, ion exchange membranes, and electrode systems. During operation, ions continuously migrate under the action of an electric field, achieving continuous deionization. If current is applied suddenly, frequent startup and shutdown operations occur, or the system is directly put into operation after a long period of shutdown, it may easily lead to: local concentration polarization, dehydration of the resin bed, scaling on membrane surfaces, abnormally increased current, formation of air bubbles and dead zones inside the module. 

These problems will gradually reduce the desalination efficiency of the system and shorten the service life of electrodeionization modules. Therefore, for any industrial user, establishing standard operating procedures (SOPs) is the foundation for ensuring long-term stable operation of the system.

Pre-Startup Inspection and Preparation

Before starting the EDI system, it is recommended to conduct inspections from three aspects: water quality, equipment, and electrical system.

1. Confirm RO Product Water Quality

EDI is not a "universal purifier"; it has strict requirements for feed water quality.

Recommended Inspection Items

Among these parameters, excessive hardness is one of the most common causes of scaling in EDI systems.

2. Check Pipeline and Valve Conditions

Before startup, confirm that: the concentrate valve is in the correct position, the product water valve is open, the air vent valve is functioning properly, there is no leakage in the pipeline system, pressure gauges and flow meters are operating normally. Many EDI failures are not caused by complicated technical problems but by incorrect valve positions.

3. Check the Electrical System

Before startup, confirm: the power supply voltage is normal, the grounding system is reliable, the PLC and touch screen are operating properly, the alarm system is in standby mode. Especially in large-scale EDI water purification systems, the automatic control system is usually responsible for the entire startup and shutdown logic. Once instrumentation abnormalities occur, the entire ultrapure water system may be forced to stop.

Standard Startup Procedure for EDI System

Step 1: Low-Flow Flushing and Air Removal

After a long shutdown period, air may remain inside the EDI module.At this time, the feed water pump should first be started, and the system should operate at a low flow rate for 5–15 minutes to fully remove the trapped air.

Startup Flow Diagram

If the air is not completely removed before applying current, it may cause local overheating and membrane damage.

Step 2: Gradually Establish the Design Flow Rate

After air removal is completed, the flow rate should be gradually increased to the designed value. The following parameters should be closely monitored: feed water pressure, concentrate flow rate, recovery rate. Excessive flow fluctuations can cause uneven ion migration and affect product water stability.

Step 3: Slowly Apply Electrical Current

This is the most critical step during the entire startup process.The correct procedure is:

① Establish stable water flow;

② Confirm that pressure is within the normal range;

③ Increase current gradually in stages;

④ Reach the designed operating current.

Applying power under dry conditions is strictly prohibited, and full-load current should never be applied instantly.For systems applied in Electrodeionization For Boiler Feed Water, the current loading process is particularly important because boiler feed water usually requires high resistivity and long-term stable operation.

Step 4: Confirm Key Operating Parameters

After the system has been running for 30 minutes, it is recommended to record the following data:

These operating data will serve as important references for future troubleshooting and performance analysis.

Key Operating Points During Stable Operation

Many enterprises believe that EDI is a "maintenance-free device". However, this is actually a misunderstanding.

An efficiently operating EDI Water Treatment System requires continuous monitoring and management of operating data.

1. Continuously Monitor Water Quality Changes

The following parameters should be monitored closely: RO product water conductivity, EDI product water resistivity, Silica concentration, TOC value.

If the performance of the RO system declines, the EDI system will usually first show symptoms such as increased current consumption and reduced product water quality. Therefore, EDI can also be regarded as an "indicator" of the operating condition of the entire ultrapure water system.

2. Control Operating Pressure and Temperature

Excessive pressure will increase module pressure drop. Insufficient temperature will reduce ion migration efficiency. Under normal operating conditions: maintain water temperature between 5–35℃, avoid frequent pressure fluctuations, prevent sudden water interruption. Stable hydraulic conditions are essential for maintaining consistent ion transfer efficiency inside the EDI module.

3. Establish an Operation Record System

It is recommended to establish a daily operation record sheet: Date → Resistivity → Current → Pressure Differential → Temperature.

Many failures do not occur suddenly but gradually develop over several weeks or even months.Through trend analysis, operators can identify potential issues in advance, including: membrane fouling, scaling risks, declining RO performance, module aging.

This is especially important for large-scale electrodeionization for power plants projects, because the economic losses caused by unexpected shutdowns are often much higher than routine maintenance costs.

Standard Shutdown Procedure for EDI System

Normal Shutdown Steps

The correct shutdown sequence is:

Stop applying electrical current → Maintain feed water operation for 5–10 minutes → Stop the feed water pump → Close related valves

The purpose of this process is to use continuous water flow to remove residual ions and gases remaining inside the module.

Short-Term Shutdown Protection

If the shutdown period is less than 48 hours, keep the module filled with water, start circulation periodically, avoid exposure to high temperatures and direct sunlight. Many EDI module failures do not occur during operation but are caused by dehydration during shutdown periods.

Long-Term Shutdown Preservation Measures

If the shutdown period exceeds one week, protective measures should be taken:

● Flush with qualified purified water;

● Remove trapped air;

● Add preservation solution according to manufacturer requirements;

● Regularly check the preservation condition.

Long-term drying may cause ion exchange membranes to shrink, affecting the recovery of subsequent performance.

Common Problems During Startup, Shutdown and Operation

1. Decreased Product Water Resistivity

Possible causes: deterioration of RO product water quality, insufficient current, module contamination, aging of ion exchange resin.

When product water resistivity decreases, operators should first check whether the upstream RO system is providing qualified feed water.

2. Increased Pressure Differential

Possible causes: scaling, particle contamination, biological contamination.

An increasing pressure differential usually indicates that flow resistance inside the module is increasing, which may affect water distribution and ion migration efficiency.

3. Abnormally Increased Current

Possible causes: increased feed water conductivity, improper recovery rate settings, scaling inside the module.

A continuous increase in operating current usually indicates that the EDI system is working under a higher ion load or internal resistance has changed.

4. Frequent Module Alarms

Possible causes: instrumentation failure, flow fluctuations, power supply abnormalities.

When frequent alarms occur, operators should check the complete system rather than only focusing on the EDI module itself.

EDI Troubleshooting Flow Diagram

Conclusion: Standardized Operation Is the Key to Long-Term Stable Operation of EDI Systems

For any industrial ultrapure water project, equipment performance is only the foundation. Standardized operation and effective management are the key factors that truly determine system service life and operating costs.

A well-operated EDI Water Treatment System can not only continuously provide high-quality ultrapure water but also reduce downtime, lower maintenance costs, and extend equipment service life. Whether it is applied in electronic industry ultrapure water systems, pharmaceutical purified water systems, boiler feed water treatment, or power industry applications, establishing comprehensive startup, shutdown, and operation standard operating procedures is the best practice for ensuring long-term stable operation of EDI systems.

When enterprises standardize daily operations, implement systematic data management, and adopt preventive maintenance strategies, the advantages of EDI technology can be fully utilized, achieving efficient, stable, and cost-effective high-purity water production.