WaterSolutions More About Troubleshooting a DOWEX™ Resin System

Typical Problems and General Causes
Common problems encountered by a water treatment plant user include insufficient throughput (plant capacity) between regenerations; poor product water quality; increased rinse volume following regeneration; or high pressure drop across a vessel, leading to insufficient flow rate.

Any one or a combination of the following may be the cause:

• Change of Raw Water Composition
• Incorrect Process Parameters
• Mechanical Failure of Equipment
• Poor Ion Exchange Resin Performance

From our experience, the majority of troubleshooting cases are related to mechanical, equipment, or operational failures. It is therefore recommended to take a wide view of the whole plant operation (including the pretreatment) when troubleshooting.


Change of Raw Water Composition
A change in raw water composition directly impacts on the plant throughput. Normally, it should not affect the product water quality unless allowing the same volume throughput on the higher salinity feedwater overruns the end-point.

A change in the ionic composition of the water can also affect throughput and water quality, even if the salinity remains unchanged. For example, an increase in sodium to total cations may lead to sodium leakage from the cation if the acid regeneration level is not adjusted to compensate. Similarly, an increase in free mineral acidity (FMA) will shorten the throughput of an anion resin after a degassifier.

Feed temperature can also have a profound affect on the operating capacity of weak acid cation and weak base anion resins. High temperatures can degrade the resin, especially acrylic and Type II anions.

Faulty pretreatment can lead to increased suspended solids, which cause higher pressure drop and potential blockage. This triggers flow channeling, thereby reducing both water quality and plant throughput. Inadequate pretreatment can also lead to slippage of oxidizing agents in the feed water, such as free Cl₂ or polyelectrolytes, thereby damaging the resin and impairing plant performance.

Performing periodic analysis of the incoming water is recommended. The frequency will depend on the stability of the water source and can only be determined by experience.

Incorrect Process Parameters
Typical problems include incorrect regeneration conditions (amount, concentration, injection time), inadequate flow rates and improper backwash, which can lead to blockage and flow channeling. Excessive or insufficient flow rates can also cause operational problems due to channeling.

Mechanical Failure of the Equipment
Pumps and measuring equipment should be checked and, if faulty, restored to good working order or replaced. In the case of poor water quality, valves should be checked to ensure no leakage of regenerant into the service water, or raw water into the treated water, is occurring. Flow distribution problems are caused by improper, blocked or broken distribution systems.

Poor Ion Exchange Resin Performance
Changes in the ion exchange resin characteristics, such as degradation or fouling, can create quality, rinse and throughput problems. Whenever resin fouling or bead breakage is suspected, a representative resin sample should be submitted to the Dow Liquid Separations Technical Service and Development laboratories for analysis. Dow offers a comprehensive range of analytical services under the System Optimization Services program.