Answers to common questions about reverse osmosis membrane and ion exchange resin (71-80)

71. Oil or other hydrophobic substances are harmful to the membrane, but why can silicone grease be used as a lubricant?

This is because the high viscosity properties of Dow Corning 111 (Dow Corning 111) prevent it from entering the membrane surface.

72. Can reverse osmosis remove microorganisms such as viruses and bacteria?

Reverse osmosis (RO) is very dense and has a very high removal rate for viruses, bacteriophages and bacteria, at least above 3log (removal rate >99.9%). However, it should also be noted that in many cases, microorganisms may still re-grow on the water production side of the membrane, which mainly depends on the way of assembly, monitoring and maintenance, that is, the ability of a system to remove microorganisms depends on the key Whether the system design, operation and management are appropriate is not the nature of the membrane element itself.

73.  Dow FILMTEC NF90 - 400, NF270 - 400, NF200 - 400 and BW30LE - 440, XLE - 440’s  product water center pipe diameter is larger, do you need special inner joints and adapters?

Each of Dow’s above components is equipped with an internal connector, and the component adapter is provided by the pressure shell manufacturer. Please inform the shell supplier in advance about the selected component model so that it can provide you with the corresponding end plate adapter.

74. How does temperature affect the water production?

The higher the temperature, the higher the water production, and vice versa. When operating at a higher temperature, the operating pressure should be lowered to keep the water production unchanged, and vice versa. Please refer to the relevant chapters for the temperature correction coefficient TCF of the change of water production.

75.  What is membrane compaction? Why did it happen?

Under the synergistic effect of high temperature and high pressure conditions, the phenomenon of membrane compaction will occur. As a result, the water production or the output of the system will decrease. Compaction is an irreversible decay of membrane performance. In fact, composite membranes are better than cellulose acetate membranes. It is more resistant to pressure densification, but frequent water hammer will also cause the film to be densified and must be avoided.

76.  After adding SMBS (sodium bisulfite) reducing agent, the water may still be oxidizing, why?

It is found that even after adding SMBS, the water may still be oxidative, and metal ions such as Fe and Cu will strengthen this tendency, which is most common in seawater desalination systems. The synergistic effect of NaCl, NaHCO3 and copper can promote this oxidizing ability. In severe cases, the oxidation-reox potential (ORP) should be used for monitoring.

77.  What is the temperature range of Dow FILMTEC dry and warm film?


78. Can formaldehyde (also known as formalin) solution be used as a protective fluid for membrane systems or components?

We do not recommend it for the following reasons:   It is suspected of having a carcinogenic tendency;

Under certain conditions (especially within 6 hours of the initial operation of the new membrane) will cause a decrease in water production. To use it, you must pay attention to this.

79.  What is particle and colloid pollution? How to measure?

Once the fouling of particles and colloids occurs in the reverse osmosis or nanofiltration system, it will seriously affect the water production of the membrane and sometimes reduce the desalination rate. The early symptom of colloidal fouling is the increase of the system pressure difference. The source of particles or colloids in the water source of the membrane inlet varies from place to place, often including bacteria, sludge, colloidal silicon, iron corrosion products, etc. Aluminum and ferric chloride or cationic polydielectrics, if they cannot be effectively removed in clarifiers or media filters, may also cause fouling. In addition, the cationic polydielectric will also react with the anionic scale inhibitor, and its sediment will foul the membrane plugging components. SDI15 is used to evaluate the fouling tendency or pretreatment of water. Please refer to the relevant chapters for detailed introduction.

80. What kind of scale inhibitor is allowed for Dow FILMTEC membrane elements?

There are a variety of commercial scale inhibitors available on the market. Its scale inhibition performance and compatibility with membranes have been tested by scale inhibitor manufacturers and water treatment system suppliers for a long time. Whether it is applicable should be confirmed by the scale inhibitor supplier. The water treatment system engineering company will be responsible for the user to select the scale inhibitor most suitable for the system situation (water type) based on their rich engineering experience.

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