Frequently Asked Questions about Reverse Osmosis Equipment (Part 1)

I. Reverse Osmosis Equipment How often should the system be cleaned?

1. Generally, when the standardized flux drops by 10-15%, or the system desalination rate drops by 10-15%, or the operating pressure and inter-stage pressure difference increase by 10-15%, the RO system should be cleaned. The cleaning frequency is directly related to the degree of system pretreatment.

2. When SDI15 < 3, the cleaning frequency may be 4 times a year.

3. When SDI15 is around 5, the cleaning frequency may double.

4. However, the cleaning frequency depends on the actual situation of each site.

II. Reverse Osmosis Equipment Manufacturer What is SDI?

1. A currently effective technique for evaluating the potential colloidal contamination of the feed water in RO/NF systems is to measure the Silt Density Index (SDI, also known as the fouling index) of the feed water. This is an important parameter that must be determined before RO design. During RO/NF operation, regular measurements must be taken (2-3 times a day for surface water). AST D4189-82 specifies the standard for this test. The feed water specification for membrane systems is that the SDI15 value must be ≤5. Effective pretreatment techniques for reducing SDI include multi-media filters, ultrafiltration, and microfiltration. Adding polyelectrolytes before filtration can sometimes enhance the ability of the above physical filtration to reduce the SDI value.

2. Should reverse osmosis or ion exchange be chosen for general water supply?

Under many feed water conditions, both ion exchange resin and reverse osmosis are technically feasible. The choice of process should be determined by economic comparison. Generally, the higher the salt content, the more economical reverse osmosis is. The lower the salt content, the more economical ion exchange is. Due to the widespread popularity of reverse osmosis technology, the combination of reverse osmosis + ion exchange, multi-stage reverse osmosis, or reverse osmosis + other deep desalination technologies has become a recognized technically and economically more reasonable water treatment solution.