To reduce failures and reduce the frequency of reverse osmosis cleaning, the following measures should be taken.
- Design the reverse osmosis system on the basis of obtaining a complete analysis of water quality;
- Determine the RO inlet SDI value before designing;
- If the influent water quality changes, corresponding design adjustments need to be made;
- Adequate pretreatment must be ensured;
- Choose the correct membrane element, cellulose acetate membrane or low pollution membrane element may be more suitable for the treatment of more complicated surface water or sewage;
- Choose a more conservative water flux;
- Choose a reasonable water recovery rate;
- Design sufficient lateral velocity and concentrated water velocity;
- Standardize the operating data.
The product water flow rate and salt permeability after “standardization” can be used to find the fault. Divided into online research and offline research.
When the salt permeability of a pressure vessel is found to be high, you need to measure the product water conductivity of each membrane element to determine the origin of the problem. Use a plastic or stainless steel tube to sample the conductivity of the product water tube at different locations to measure the conductivity. Marks can be made on the position of these marks is equivalent to the position to be sampled. The sampling tube is first inserted into the farthest end of the product water pipe, the conductivity is measured by sampling, and then drawn back section by section to obtain the conductivity change curve. When the feed water flows through the pressure vessel, it gradually becomes thicker, causing the product water concentration to increase. The conductivity of the sampled sample changes from the previous swim to the next membrane element. The change in conductivity is about 10%. If this change is too large, it indicates the problem If the conductivity changes at a certain point, it indicates mechanical leakage. From the analysis of the change in the ratio of divalent ions to monovalent ions in the product water, it can also be inferred whether leakage has occurred.
Non-destructive off-line research of roll-type membrane elements has only one method of vacuum test, (It is the American ASTM standard, B3923). If the vacuum damage exceeds 20kPa per minute, that is, 6in Hg, it means that the membrane element is seriously leaking and cannot be used again. If the test does not reveal the problem, a destructive (anatomical) analysis may be required to check the internal conditions of the membrane element, test the components and analyze the contaminants.