Answers to common questions about reverse osmosis membrane and ion exchange resin (31-40)

31. When should low-energy or very low-energy membrane elements be used?

Dow FILMTEC’s low-energy membrane elements are of the LE and LP type, and the extremely low energy consumption is XLE. They are used for customers who require the lowest energy consumption while still achieving a high desalination rate and water production for the main purpose. For example, the energy consumption of our extremely low energy XLE is only 50% of the corresponding energy consumption of standard BW products, but the desalination rate is low, please consult a Dow representative or refer to the product specification.

32. What is the relationship between influent TDS and conductivity?

When the influent conductivity value is obtained, it must be converted into a TDS value so that it can be entered during software design. For most water sources, the conductivity/TDS ratio is between 1.2 and 1.7. For ROSA design, 1.4 ratio is used for seawater and 1.3 ratio is used for brackish water conversion. Usually, a good approximate conversion rate can be obtained.

33. How do I know if the membrane has been contaminated?

The following are the common symptoms of pollution: 1 under standard pressure, the water production decreases; 2 in order to achieve the standard water production, the operating pressure must be increased; 3 the pressure drop between the influent and concentrated water increases; 4 the weight of the membrane element increases; 5 membrane The removal rate changes significantly (increase or decrease)
When the element is taken out of the pressure vessel, pour water on the water inlet side of the erected membrane element. The water cannot flow through the membrane element and only overflows from the end surface (indicating that the inlet water channel is completely blocked).

34. When do I need to detect the membrane system, how to do it?

The reduction of the desalination rate of the system may be a uniform change of the elements, or it may be limited to a few membrane elements at the front or end. It may be a failure of each pressure vessel of the entire system, or it may be limited to a few pressure vessels. Therefore, you need to determine the TDS value of the water produced by a single pressure vessel and the performance of a single membrane element. Please refer to the relevant chapters of this manual for the membrane element performance detection method.

35. How to prevent the growth of microorganisms in the original packaging of the membrane element?

When the protective solution appears cloudy, it is likely due to the growth of microorganisms. Membrane elements protected with sodium bisulfite should be checked every three months. When the protective solution appears cloudy, the components should be removed from the sealed storage bag and re-soaked in fresh protective solution, the concentration of the protective solution is 1% (weight) food grade sodium bisulfite (not activated by cobalt), soak for about 1 hour , And reseal it, and drain the components before repackaging.

36. What is the weight of the Dow FILMTEC membrane element?

Dow FILMTEC new component weight list.

Type No.Dry elementWet components*
XLE-4040
LP-4040
TW30-4040
2.33.2
BW30-4040
BW30LE-4040
NF90-4040
NF270-4040
NF200-4040
NF-4040
2.73.6
BW30-36511.314.1
BW30-40011.814.5
RO-390-FF
NF90-400
NF270-400
NF200-400
NF-400
/14.5
XLE-440
BW30LE-440
12.715.0
SW30HR-320/13.6
SW30HR-380
SW30-380
/14.1

* Note: Wet components are the weight after draining
The degree of fouling can be judged according to the weight of the used components, and the weight of some heavily fouled membrane components may more than double.

37. How can the energy consumption of the membrane system be reduced?

It is sufficient to use low-energy membrane elements LP, BWLE or extremely low-energy membrane elements XLE, but it should be noted that their desalination rate is slightly lower than standard membrane elements.

38. Should the air in the system be expelled before the membrane system is turned on?

We require that the air must be driven away with low pressure and low flow rate in order to start the membrane system. The pressure of this operation is between 0.2 and 0.4 MPa. When flushing and exhausting at low pressure, all concentrated water and product water should be discharged into the sewer. If the pressure rises too fast and there is still air in the membrane element and pressure vessel, It will generate additional impact force in the water flow direction and radial direction of the element, and in severe cases will rupture the outer skin of the membrane.

39. How are Dow wet components protected?

The wet element is protected with 1% by weight sodium bisulfite, and the ultrapure water polishing membrane element is protected with 500 ppm by weight sodium bisulfite.

40. What are the requirements for pressure vessels?

The design of the pressure vessel must comply with the American Society of Mechanical Engineers Standards (ASME), and it is best to obtain ASME standard certification, or at least it should be manufactured in accordance with ASME standard requirements.

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