What is reverse osmosis membrane heavy contamination

As a means of deep filtration, reverse osmosis membrane elements will inevitably have colloids, microorganisms, impurity particles and insoluble salts precipitating on their surface, so reverse osmosis units used in a variety of fields will eventually need to be cleaned once they are in use, just at different intervals. However, online cleaning as a means of cleaning and maintenance, impact sterilisation and periodic protection of reverse osmosis systems is not sufficient when faced with heavy contamination of reverse osmosis membrane elements, and offline cleaning of reverse osmosis membrane elements is required.

What is heavy contamination of a reverse osmosis membrane element?

This refers to the surface attachment, deposition contamination or chemical scale generation of suspended matter, colloids, organic matter, microorganisms and other particles in the feed water of a reverse osmosis system to the RO membrane. Heavy contamination refers to the situation where the pressure difference of a single section after contamination is greater than 2 times the pressure difference of a single section at the beginning of system operation, and the water production of the RO system drops by more than 30% or the weight of a single RO membrane element exceeds the normal value by more than 3 kg.

Heavy contamination is often a combination of heavy physical and heavy chemical contamination, and in some cases, both at the same time.

Causes and characteristics of heavy contamination of reverse osmosis membrane elements

Due to the different water quality of water sources around the world, and the treatment methods used are not the same, so the reasons for RO membrane elements are not the same, the common causes and characteristics of pollution are as follows.

1. Water treatment process system design and manufacturing defects

① For reverse osmosis pretreatment filter, the source water is not well water, the equipment filtration speed is greater than 8.5 m / h, while the surface water design equipment filtration speed is greater than 8 m / h, resulting in reverse osmosis feed water SDI exceeds the standard.

② The source water contains impurities such as colloids and suspended matter, which are not removed in the design.

③ COD>3 in the source water without removal measures.

④ Reverse osmosis membrane element design flux exceeds the standard of the reverse osmosis device second section fouling and differential pressure rise fast, water production decay and desalination rate decline fast.

2. Improper selection of reverse osmosis additives and other consumables

①Improper choice of reverse osmosis scale inhibitor type or dosage, such as: the type of reverse osmosis scale inhibitor is not compatible with the source water, such as the source water contains aluminum ions, iron ions or pretreatment dosing with iron, aluminum and other flocculants, as far as possible to choose the organic anti-scaling agent, try to avoid the use of polycarboxylic acid type; reverse osmosis scale inhibitor dosage is generally between 2-4ppm (calculated according to the inlet water), at most can not exceed 6ppm, etc., the type of scale inhibitor and dosage of improper choice will lead to a rapid decline in system water production, the system pressure differential increased significantly.

② Reverse osmosis security filter cartridge in the selection process to ensure reliable quality, claiming 5 microns but the actual accuracy of the cartridge does not reach the safe operation of the reverse osmosis membrane element is very detrimental.

③ Improper selection of flocculants and coagulants in the reverse osmosis pretreatment system will cause serious contamination of the membrane element, while improper selection of biocides makes serious damage to the desalination rate of the reverse osmosis system; (containing Cl-).

3. Abnormalities in the system caused by sudden changes in the operating conditions of the water treatment.

Generally due to climate change resulting in an increase in the content of suspended matter in the source water, or a change in the type of source water (for example: from groundwater to tap water resulting in an increase in the residual chlorine content in the reverse osmosis feed water) when the reverse osmosis unit operating conditions deteriorate, the formation of heavy pollution.

4. System operation and management problems

① Failure to operate according to operating procedures.

② untimely adjustment of equipment status parameters.

③ Improper adjustment of operating parameters.

④The measurement of added chemicals is not optimised.

⑤ Not cleaning the system in time when the system reaches the cleaning condition.

⑥ The system is not adjusted on time.

⑦ Lack of operation management summary.

5. Water treatment system water supply tension

In addition to the above, in a considerable number of enterprises, due to water treatment system water supply tension, making the reverse osmosis device even if the deterioration of operating parameters, the system suffers from pollution, but because of the water supply tension and can not be timely cleaning, resulting in system pollution gradually serious, the formation of heavy pollution.