Determining the Type of Contamination in an Ultrapure Water System

During the use of an ultrapure water system, its performance gradually declines with use. Besides normal performance degradation, contamination can cause even more severe performance degradation. There are many types of contamination in ultrapure water systems. So how do we determine the type of contamination?

Identifying the type of contamination requires a comprehensive assessment of raw water quality, design parameters, contamination index, operating records, changes in equipment performance, and microbiological indicators:

1. Colloidal Contamination: Colloidal contamination is usually accompanied by the following two characteristics:

A. The microfilter in the pretreatment stage clogs rapidly, especially with a rapid increase in pressure differential.

B. The SDI value is usually above 2.5.

2. Microbial Contamination: When microbial contamination occurs, the total bacterial count in both the RO permeate and concentrate is relatively high, indicating a lack of proper maintenance and disinfection.

3. Calcium Scale: This can be determined based on the raw water quality and design parameters. For carbonate-type water, if the recovery rate is 75% and scale inhibitors are added during the design, the LSI of the concentrate should be less than 1; if no scale inhibitors are added, the LSI of the concentrate should be less than zero, and calcium scale generally will not form.

4. A 1/4-inch PVC plastic tube can be inserted into the component to test the performance changes of different parts of the component for judgment.

5. The type of contamination can be determined based on the changes in equipment performance.

6. Acid washing (such as citric acid, dilute HNO3) can be used to determine calcium scale based on the cleaning effect and the cleaning solution, and further confirmed by the composition analysis of the cleaning solution.

7. Chemical analysis of the cleaning solution: take three samples for analysis: raw water, cleaning solution, and cleaning solution. When the type of contamination cannot be determined, the cleaning steps of cleaning (3) + disinfection + 0.1% HCl (pH 3) are usually adopted.