Reverse osmosis system - Fault phenomena

The fault phenomena of reverse osmosis systems mainly fall into three categories:

     Reduced water permeability

     The salt permeability increases(The desalination rate has decreased),

     Increased pressure drop

    There are many causes of these malfunctions. By identifying the essence of the problem from these malfunction phenomena, corresponding solutions can be found!

I. External Factors Causing Faults

1Reverse osmosis failure caused by changes in the quality of the influent water

◆ Changes in influent water quality;

◆ The pretreatment system cannot be optimized.

2Reverse osmosis faults caused by pretreatment

◆ The filter material of the multi-media filter is disordered or has an uneven flow.

◆ The buffer water tank and microbial reproduction are severe.

◆ The filter material of the activated carbon filter is severely powderized or infested with microorganisms.

3Reverse osmosis failure caused by the security filter

◆ The diameter of the security filter is too small.

◆ The quality of the filter element is poor and the filtration accuracy fails to meet the requirements.

◆ The filter element cannot be pressed tightly and is prone to deformation.

4Reverse osmosis faults caused by the scale inhibitor dosing system

◆ The performance of the scale inhibitor does not match the water quality.

◆ The performance of the scale inhibitor metering pump is unreliable.

◆ Excessive dilution of the scale inhibitor and severe contamination of the medicine tank;

◆ The addition of scale inhibitors causes flow deviation.

5Reverse osmosis faults caused by other dosing systems

◆ Inappropriate flocculants cause membrane element contamination.

◆ Excessive addition of oxidants causes the membrane elements to be oxidized.

◆ Excessive addition of reducing agent causes severe fouling of membrane elements.

6Reverse osmosis faults caused by instruments and meters

◆ The concentrated water flow rate is shown to be too large (actually too small), which causes the reverse osmosis recovery rate to be too high and leads to scaling.

◆ The concentrated water flow rate is shown to be too small (actually quite large), which causes the reverse osmosis recovery rate to be too low and generates an excessive pressure difference.

◆ Fluctuations in flow readings cause system judgment errors.

Ii. Analysis of Common Faults of Reverse Osmosis

The reverse osmosis device malfunctions

Faults of reverse osmosis devices can generally be analyzed from three aspects:

◆ System design joint

◆ Installation and commissioning stage

◆ Operation and maintenance link

(1System design stage

◆ Raw water quality and special ions - Comprehensive water quality analysis and special ions such as iron, manganese, and silicon;

◆ Water temperature - Design and calculate based on the actual operating water temperature;

◆ Recovery rate - The recovery rate is determined based on the arrangement of membrane elements to prevent the water flux of individual membrane elements from exceeding the standard.

◆ Number of membrane elements - Ensure that the average water production of each membrane element is less than1Tons of/Hours;

◆ Back pressure of product water - Calculate the back pressure of product water appropriately based on the transportation conditions of the product water.

◆ Operating life - generally needs to be simulated3To ensure the reliability and sufficiency of the high-pressure pump selection, the operating life of reverse osmosis can be extended by a certain number of years.

Ignore6This key point is prone to cause relatively serious malfunctions and adverse effects

1.With the extension of the operating years of reverse osmosis and the change in water temperature, when the high-pressure pump reaches full load output, the water production still fails to reach the initial design value.

2.The higher pressure on the water production side causes the high-pressure pump to still fail to reach the initial design value even when it reaches full load output.

3.The number of membrane elements configured in reverse osmosis is small, which means that as the operating years extend, a higher feed water pressure is required to maintain a stable water production volume.

4.The recovery rate of reverse osmosis exceeds the normal value, and the rate of contamination accelerates.

(2Installation and commissioning stage

◆ Security filter - Strictly control the tightness of the installation of the security filter element and ensure it is compacted.

◆ Instruments and meters - The flow probe should maintain the inlet1.5Rice, export1The meter is equipped with a saddle-shaped probe base.

◆ Flush the pipeline system - When flushing the system pipelines, install the filter element of the security filter to prevent large particles from depositing on the reverse osmosis device and its related pipelines.

◆ Reverse osmosis membrane installation - When installing membrane elements, medical glycerin should be used and the use of lubricating substances such as detergent should be avoided as much as possible.

◆ Scale inhibitor addition - During the initial commissioning, it is necessary to ensure the normal addition of scale inhibitors and other chemicals to prevent the membrane elements from being contaminated and scaling after the commissioning time is prolonged.

◆ Salt water sealing ring - When installing membrane elements, check the installation direction of the salt water sealing ring.

◆ Pollution indexSDI-- Water has entered the test systemSDIThe value remains3Within.

Ignore7This key point is prone to cause relatively serious malfunctions and adverse effects

1.Severe mechanical fouling, especially the membrane elements are prone to being scratched by sharp impurities.

2.The reading of the flowmeter is unstable and cannot play a monitoring role.

3.OThe wear of the ring and the salt water sealing ring has occurred, resulting in a decline in the quality of the produced water and a relatively high recovery rate.

4.A large pressure difference causes the membrane element to produce a telescope effect, including a section of pressure difference caused by fouling and clogging.

3Operation and maintenance phase

◆ Instruments and meters - Regular calibration of flow meters and regular cleaning of probes;

◆ Pressure gauge - Regular calibration of pressure gauges;

◆ Pressure vessels - Correct disassembly and installation of pressure vessel end plates;

◆ Concentrated water thrust ring - Correct placement of concentrated water thrust ring;

◆ Upper limit of operating data - Determine the upper limit of operating parameters such as the pressure difference between sections, and handle it promptly when the upper limit is reached.

◆ Manual cleaning - For severe mechanical fouling, it is necessary to prevent the use of overly strong water jets for flushing.

Iii. Neglect6This key point is prone to cause relatively serious malfunctions and adverse effects

1.A high recovery rate occurs when the brine sealing ring is installed in reverse.

2.The thrust ring of the pressure vessel overlaps or partially overlaps with the concentrated water outlet, generating high recovery rate operation.

3.The mixed use of new and old membrane elements or different types of membrane elements has accelerated the rate of pollution.

4.If the flowmeter display is too large or too small, it will affect the adjustment of the system's recovery rate.

5.Excessive pressure difference causes the membrane elements to be mechanically fractured, resulting in irreparable losses.

6.Inaccurate operating pressure can easily put the system in an overloaded operation state, accelerating the pollution rate.

Engineer of Beijing Yuanlai Water Treatment Technology Regarding the process design, operation and maintenance management of the entire reverse osmosis system, pay attention to details, and promptly analyze and provide solutions to any problems that arise or may occur.

      Fundamentally ensure the long-term stable operation of the reverse osmosis system, improve operational efficiency, minimize system consumption to the greatest extent, and save operational cost expenditures!

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