Fault Analysis of Reverse Osmosis Water Treatment Equipment

Author: Hongjie Water 

Reverse osmosis, also known as Reverse osmosis, is a membrane separation operation that uses pressure difference as the driving force to separate solvent from solution. Because it is opposite to the direction of natural infiltration, it is called reverse osmosis.

Faults caused by poor inlet water quality

In the initial design, due to the good inlet water quality, the system operation was relatively stable. However, as the subsequent inlet water quality deteriorated, the reverse osmosis device experienced serious operational failures when the system could not be optimized for pre-treatment.

Fault manifestation

The decay rate of water production is fast, and the operating pressure and pressure difference increase rapidly.

Failure caused by performance degradation in preprocessing

Due to the poor performance of the pre-treatment equipment, the turbidity, SDI value, COD value, etc. of the effluent seriously exceed the requirements of the influent water quality.

Fault manifestation

Broken CMF or UF membrane wires; Severe bacterial and microbial proliferation in the buffer water tank; Multi media filter media with disordered layers or bias flow; The filter material inside the activated carbon filter has severe pulverization or microbial proliferation.

Malfunctions caused by the use of inferior filter elements in security filters

When the output of the security filter increases, the filter element is prone to deformation or the filtration accuracy cannot meet the requirements, causing pollutants to directly enter the interior of the reverse osmosis device.

Fault manifestation

The diameter of the security filter element is too small; The quality of the filter element is poor, and the filtration accuracy cannot meet the requirements; The filter element is not tightly pressed and is prone to deformation.

Malfunctions caused by improper selection and dosing of scale inhibitors

As the "protective god" for the safe and stable operation of reverse osmosis, scale inhibitors have become the mainstream of current scale inhibition forms due to their excellent effects and low operating costs. However, many problems have arisen in the selection, dosing, and mixing of scale inhibitors.

Fault manifestation

The performance of scale inhibitors does not match the water quality; The performance of the scale inhibitor metering pump is unreliable; Excessive dilution of scale inhibitors; The scale inhibitor metering tank is severely contaminated.

Malfunctions caused by improper dosing of other chemicals

A certain amount and category of chemicals need to be added to improve the treatment effect of raw water for different water qualities. However, due to various reasons, improper use and addition of these chemicals can have serious consequences.

Fault manifestation

Unsuitable flocculants cause serious membrane fouling; Excessive addition of oxidants causes membrane oxidation; Excessive addition of reducing agent causes serious fouling and blockage of the membrane.

Malfunctions caused by instrument malfunctions

At present, imported digital display instruments are commonly used on reverse osmosis devices. Some instruments, under the premise of correct installation, display flow very accurately and have stable readings; However, other types of digital display instruments have a relatively large range of numerical fluctuations during operation, especially some instruments with parameter setting functions, and the displayed water production is controlled by human factors. Such instruments, which act as the eyes of reverse osmosis, will affect the judgment of technical personnel on reverse osmosis.

Fault manifestation

1. The display of concentrated water flow rate is too high (actually small), which causes excessive reverse osmosis recovery rate and scaling;

2. The display of concentrated water flow rate is too small (actually large), which leads to low reverse osmosis recovery rate and pressure difference;

3. The reading of the flow meter fluctuates excessively, making it difficult to accurately judge at a ratio of 10-15%.

Faults caused by device design defects and improper operation and maintenance

There are many problems with reverse osmosis devices, with some systems having defects in design and some deviating in daily operation and maintenance, causing serious operational hazards.

Fault manifestation

1. In the initial design, the head selection of the high-pressure pump was too low, which caused the water yield to not meet the design requirements when the temperature or inlet water quality changed;

2. The oxidation of membrane components causes an increase in water flux and a decrease in the quality of produced water;

3. The inversion or damage of the saline sealing ring causes excessive actual recovery rate, resulting in scaling and water quality degradation;

4. The damage of the O-ring causes a decrease in the quality of the produced water;

5. The mixed use of new and old membrane components and different types of membrane components leads to a decrease in system performance;

6. The concentrated water thrust ring of the pressure vessel overlaps or partially overlaps with the concentrated water outlet, causing high recovery rate and scaling phenomenon;

7. The length of the pressure vessel is too large, causing concentrated water to leak to the production side, resulting in a decrease in the quality of the production water;

8. No interval pressure gauge can reliably analyze and judge the operation of reverse osmosis;

9. The large pressure difference causes damage to the membrane element due to telescope effect;

10. The increase in water production backpressure causes a decrease in water production;

11. The unreasonable arrangement of reverse osmosis causes an increase in the water flux of local membrane components and accelerates the pollution rate;

12. Unreasonable design of reverse osmosis recovery rate and small number of membrane components;

13. Granular pollution causes severe mechanical fouling and blockage of membrane components, resulting in a large pressure difference at one stage and a decrease in water production and quality;

14. Sedimentation of pollutants and bacterial and microbial pollution caused by system shutdown.