How to Solve Low Desalination Rate in Industrial Pure Water Systems – Troubleshooting & Optimization Guide

In the field of industrial water purification, a consistently high desalination rate is crucial for reverse osmosis (RO) system performance. However, in real-world applications, unexpected issues often emerge. This article explores a practical case from a 200m³/h RO project at a thermal power plant, where the system showed a significantly low desalination rate—dropping below 90% despite all design parameters appearing normal.

By examining this incident, we hope to provide valuable insights for engineers and plant operators facing similar issues in large-scale pure water systems.

Reviewing RO Design Parameters vs. Actual Performance

The original design of the RO system was based on treating lime-softened water, with the key feedwater parameters set as follows: pH 7.0–8.0, hardness <0.1 mmol/L, and conductivity <500 μS/cm. The expected desalination rate was over 98%.

However, during routine inspection, several discrepancies were noted:

• Actual pH value: Reached as high as 9.2
• Conductivity: Often exceeded 900 μS/cm
• Hardness: Residual hardness found around 0.4–0.6 mmol/L

These deviations significantly affected membrane performance. In particular, the elevated pH and hardness levels promoted scaling and reduced ion rejection efficiency, leading to a desalination rate that dropped to as low as 86%.

If you're facing similar issues, it’s critical to first compare your real-time water quality with your system’s design specifications to identify early warning signs of underperformance.

RO System Troubleshooting: Diagnosing the Root Cause of Low Desalination Rates

Upon identifying the mismatch between the actual feedwater parameters and the RO system's design specifications, a comprehensive diagnosis was initiated to uncover the root causes behind the declining desalination rate.

Key diagnostic actions included:

• Membrane Integrity Check: Conducted pressure vessel inspections and salt rejection tests, confirming no mechanical damage to the membranes.
• Water Quality Analysis: Tested hardness, alkalinity, and silica levels to assess the risk of scaling and fouling.
• Cleaning Records Review: Evaluated the effectiveness and frequency of chemical cleaning procedures, noting signs of inadequate descaling.
• Historical Data Comparison: Reviewed operational logs over the past six months to identify when performance degradation began.

The findings suggested that the core issue was chemical scaling due to insufficient pretreatment and elevated hardness in the feedwater. Membrane autopsy results (where available) further confirmed calcium carbonate and magnesium hydroxide fouling.

This diagnosis highlighted the importance of real-time water quality monitoring and adapting pretreatment strategies to avoid long-term membrane degradation.

How to Improve Desalination Rate: Practical Optimization Measures

After thorough analysis, several corrective actions were recommended to restore and enhance the desalination performance of the RO system:

• Enhancing Pretreatment: Integrated a softening process to reduce feedwater hardness, preventing calcium and magnesium scaling. Additional antiscalant dosing was optimized based on LSI and S&DSI values.
• Cleaning Protocol Upgrade: Implemented a more frequent and targeted CIP (Clean-In-Place) schedule using acid and alkaline cleaning agents suited for identified scaling compounds.
• Membrane Replacement: Replaced irreversibly fouled membranes while documenting performance benchmarks for long-term comparison.
• Monitoring System Improvement: Deployed real-time sensors for conductivity, pH, and differential pressure, enabling earlier detection of fouling trends.
• Operational Training: Provided hands-on training for technicians to correctly respond to changes in feedwater conditions and maintain optimal system recovery rates.

These actions not only improved the desalination rate but also extended the service life of the membranes, reduced downtime, and enhanced system stability. For plants facing similar issues, adopting these strategies can yield measurable benefits and prevent performance losses.

Conclusion: Lessons Learned from Low Desalination Rate Diagnosis

This case study demonstrated that even well-designed pure water systems are susceptible to performance decline due to overlooked pretreatment inefficiencies, inadequate monitoring, and improper maintenance. Through systematic diagnosis and tailored corrective measures, the root causes behind the low desalination rate were identified and resolved.

Key takeaways for industrial operators include:

1. Routine Monitoring is Critical: Regularly tracking key parameters like conductivity, differential pressure, and scaling indices helps preempt major failures.
2. Customized Pretreatment: Feedwater characteristics must guide pretreatment design—generic solutions can lead to irreversible membrane damage.
3. Proactive Maintenance: Periodic CIP and timely membrane replacement significantly boost operational reliability and efficiency.
4. Training Yields Returns: Empowering staff with technical understanding reduces human errors and ensures swift troubleshooting.

By sharing this operational insight, we aim to assist other industrial water treatment professionals in optimizing their reverse osmosis systems. For more support or tailored technical consultation, feel free to contact our team at STARK Water.