Diagnosis and Remediation of Performance Issues in a Demineralisation Ion Exchange System: A Case Study on Polymer Fouling and Calcium Leakage

ABSTRACT

This study investigates the root cause of performance deterioration in a demineralisation system, and ultimately identifies polymer fouling of the cation exchange resin as the primary issue. Detailed analysis revealed that surface fouling by cationic polymers selectively impaired the diffusion and exchange of divalent calcium ions due to steric exclusion effects, while monovalent sodium ion exchange remained largely unaffected. This selective interference led to calcium leakage, resulting in conductivity imbalances in the treated water.

Potential mechanical causes, including passing backwash valves that could allow untreated water to bypass the cation vessel, were systematically evaluated and ruled out based on consistent sodium concentrations within specification at the cation outlet. The findings confirmed that the observed performance issues were chemically, rather than mechanically, driven.

Restoration of system performance was successfully achieved through targeted resin treatment, demonstrating the effectiveness of a structured troubleshooting approach combining operational data analysis, resin testing, and corrective intervention. The study highlights the importance of controlling and monitoring polymer dosing in upstream pre-treatment processes to mitigate fouling risks and ensure sustained ion exchange efficiency. These results provide practical insights for diagnosing and resolving complex performance issues in demineralisation plants.

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