How to Troubleshoot Reverse Osmosis Systems and Membrane Elements

Only after the product water flow rate and salt permeation rate have been "standardized" can they be used to locate faults. This is divided into online and offline studies.

Online Study

When a high salt permeation rate is found in a pressure vessel, the product water conductivity of each membrane element needs to be measured to determine the origin of the problem. A plastic or stainless steel tube is used to sample and measure conductivity at different locations in the product water pipe. Marks can be made on the sampling tube; these marks correspond to the sampling locations. The sampling tube is first inserted to the farthest end of the product water pipe to sample and measure conductivity. Then, it is pulled back segment by segment to obtain the conductivity change curve. As the feed water flows through the pressure vessel, it gradually becomes more concentrated, causing an increase in product water concentration. The conductivity change from the previous membrane element to the next is approximately 10%. If this change is too large, it indicates a problem. If there is a dilatational change in conductivity at a certain point, it indicates mechanical leakage. The change in the ratio of divalent to monovalent ions in the product water can also be used to infer whether a leak has occurred. (2) Offline Study

The only non-destructive offline study method for spiral wound membrane elements is the vacuum test (US ASTM standard, B3923). If the vacuum deteriorates to a rate exceeding 20 kPa per minute, or 6 inches of mercury, it indicates a serious leak in the membrane element, rendering it unusable. If the test fails to reveal the problem, destructive (dissection) analysis may be necessary to examine the internal condition of the membrane element, test components, and analyze contaminants.