Author: Site Editor Publish Time: 2023-01-24 Origin: Site
In general, when the standardized flux decreases by 10-15%, or the system desalination rate decreases by 10-15%, or the operating pressure and differential pressure between segments increases by 10-15%, the RO system should be cleaned.
Cleaning frequency and system pretreatment degree has a direct relationship, when SDI15 <3, cleaning frequency may be 4 times a year; when SDI15 in about 5, cleaning frequency may have to double but cleaning frequency depends on the actual situation of each project site.
The best technique to evaluate the possibility of colloidal contamination in the feed water to the RO/NF system is to measure the silt density index (SDI, also known as the fouling index) of the feed water, which is an important parameter that must be determined before RO design.
This must be measured at regular intervals during RO/NF operation (2 to 3 times daily for surface water) and ASTM D4189-82 sets the standard for this test.
The feed water regulations for membrane systems are that the SDI15 value must be ≤ 5. Effective techniques for SDI reduction pretreatment are multi-media filters, ultrafiltration and microfiltration. Adding polyelectric media before filtration can sometimes enhance the above physical filtration and reduce the SDI value.
In many water conditions, the use of ion exchange resin or reverse osmosis are technically feasible, the choice of process should be determined by economic comparison, in general, the higher the salt content, the more economical reverse osmosis, the lower the salt content, the more economical ion exchange.
Due to the popularity of reverse osmosis technology, reverse osmosis + ion exchange process or multi-stage reverse osmosis or reverse osmosis + other depth desalination technology combination process has become a recognized technical and economic more reasonable water treatment program, for further information, please consult the water treatment engineering company representative.
The service life of a membrane depends on the chemical stability of the membrane, the physical stability of the element, the cleanability, the water source, the pretreatment, the cleaning frequency, the operation management level, etc. According to economic analysis it is usually more than 5 years.
Nanofiltration is a membrane liquid separation technology located between reverse osmosis and ultrafiltration. Reverse osmosis removes the smallest solutes with a molecular weight of less than 0.0001 microns, while nanofiltration removes solutes with a molecular weight of around 0.001 microns.
Nanofiltration is essentially a low pressure reverse osmosis and is used where the purity of the treated produced water is not particularly stringent. Nanofiltration is suitable for treating well and surface water.
Nanofiltration is suitable for water treatment systems where the high desalination rates of reverse osmosis are not necessary, but where the ability to remove hardness components is high, sometimes referred to as "softening membranes", nanofiltration systems operate at low pressure and consume less energy than the corresponding reverse osmosis systems.