Dry Goods | Reverse Osmosis Troubleshooting and Solutions

      There are three main types of malfunctions in reverse osmosis systems: reduced water permeability, increased salt passage rate ( Desalination rate decrease ) and increased pressure drop. However, there are many reasons for these malfunctions. It is important to identify the root cause of the problem from these malfunction phenomena to implement timely maintenance and other countermeasures.

　　Analysis and solutions for reverse osmosis system operation failures are mainly carried out from four aspects:
　　1. External factors causing reverse osmosis failures;
　　2. Common malfunctions of reverse osmosis devices;  
　　3. Common failure analysis of reverse osmosis systems.

1. External factors causing reverse osmosis failures
　　1 Reverse osmosis failures caused by changes in feed water quality
　　◆ Changes in feed water quality;
　　◆ The pretreatment system cannot be optimized.
　　2 Reverse osmosis failures caused by pretreatment  
　　◆ Multi-media filter media disorder or bypass;  
　　◆ Serious breeding of bacteria and microorganisms in the buffer tank;  
　　◆ Serious pulverization or microbial reproduction of activated carbon filter media.  
　　3 Reverse osmosis failures caused by security filters  
　　◆ The diameter of the security filter is too small;  
　　◆ The quality of the filter element is poor, and the filtration accuracy does not meet the requirements;
　　◆ The filter element is not tightly pressed and is easily deformed.  
　　4 Reverse osmosis failures 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 serious pollution of the chemical tank;  
　　◆ Bypass caused by scale inhibitor dosing.
　　5 Reverse osmosis failures caused by other dosing systems
　　◆ Inappropriate flocculants cause membrane element pollution;  
　　◆ Excessive addition of oxidants causes oxidation of membrane elements;
　　◆ Excessive addition of reducing agents causes serious blockage of membrane elements.  
　　6 Reverse osmosis failures caused by instruments and meters  
　　◆ Concentrate flow rate is displayed as large ( Actually smaller ) Causes excessive reverse osmosis recovery rate and scaling; 
　　◆ Concentrate flow rate is displayed as small ( Actually larger ) Causes the reverse osmosis recovery rate to be too low, resulting in a large pressure difference; 
　　◆ Flow reading fluctuations cause system misjudgment.

　　2. Common malfunctions of reverse osmosis devices  
　　1 The head of the high-pressure pump selected during the initial design is too low, causing the water production to not meet the design requirements when the temperature or feed water quality changes;  
　　2 Membrane elements are oxidized, causing increased water flux and decreased product water quality;

 　  3 The brine seal is reversed, causing the actual recovery rate to be too high, resulting in scaling and deterioration of water quality;  
　　4 The brine seal is damaged, causing the actual recovery rate to be too high, resulting in scaling and deterioration of water quality;  
　　5、 O Ring damage causes a decrease in product water quality;  
　　6 Mixing new and old membrane elements and different types of membrane elements causes a decrease in system performance;  
　　7 The concentrate thrust ring of the pressure vessel overlaps or partially overlaps with the concentrate outlet, causing the recovery rate to be too high and resulting in scaling;  
　　8 The length of the pressure vessel is too large, causing concentrate leakage to the product water side, resulting in a decrease in product water quality;  
　　9 The inter-stage pressure gauge cannot reliably analyze and judge the operation of reverse osmosis;  
　　10 A large pressure difference causes the membrane element to produce a telescope effect and damage;  
　　11 An increase in product water backpressure causes a decrease in product water volume;  
　　12 Unreasonable reverse osmosis arrangement causes an increase in water flux of local membrane elements and accelerates pollution;  
　　13 Unreasonable design of reverse osmosis recovery rate and insufficient number of membrane elements;  
　　14 Particulate pollution causes serious mechanical fouling of the membrane elements, a large pressure difference in one section, and deterioration of water production and quality;  
　　15 System shutdown causes pollutant deposition and bacterial and microbial pollution;  
　　16 Cast iron base high-pressure pump is connected in series in the chemical cleaning system pipeline;

　　3. Common failure analysis of reverse osmosis systems  
　　1 Scale inhibitor dosing system failure
　　There are three key points in the selection of scale inhibitor agents:  
　　◆ Detailed raw water quality analysis —— Detailed water quality analysis is a prerequisite  
　　◆ Reverse osmosis system conditions —— Temperature, recovery rate, arrangement method, water production, etc.  
　　◆ Using dedicated computer simulation dosing software, the system operating conditions and feed water quality can be specifically analyzed, and combined with the performance of the agent, the most cost-effective agent selection can be provided.  
　　If the three key points are not grasped well, serious consequences will occur:  
　　◆ Reverse osmosis scaling caused by incompatible chemical type
　　◆ Reverse osmosis system scaling caused by insufficient dosage
　　◆ Increased costs due to excessive dosage
　　2 Failure in the dilution and addition of scale inhibitors
　　◆ Excessive dilution can easily lead to contamination of the scale inhibitor by bacteria and microorganisms, causing reverse osmosis system scaling;  
　　◆ Incorrect selection of scale inhibitor metering pump, with outlet pressure lower than the pretreatment water pressure, resulting in insufficient chemical addition and reverse osmosis scaling;  
　　◆ Incorrect installation of the scale inhibitor metering pump, resulting in insufficient scale inhibitor dosage and reverse osmosis system scaling;  
　　When air bubbles are present in the bent pipe, the scale inhibitor cannot be reliably added.
　　3 Mixing failure of scale inhibitors
　　◆ Uneven mixing of scale inhibitors can cause slight reverse osmosis / Severe scaling;  
　　This is very likely to occur when two or more sets are running in parallel and the scale inhibitor is added through a mother pipe  
　　4 Reverse osmosis equipment failure
　　Reverse osmosis equipment failures can generally be analyzed from three aspects
　　◆ System design joints  
　　◆ Installation and commissioning stage  
　　◆ Operation and maintenance stage  
　　(1) System design stage
　　◆ Raw water quality and special ions —— Complete water quality analysis and special ions such as iron, manganese, and silicon  
　　◆ Water temperature —— Design and calculation based on actual operating water temperature  
　　◆ Recovery rate —— Determine the optimal recovery rate based on the arrangement of membrane elements to prevent exceeding the water flux of individual membrane elements  
　　◆ Number of membrane elements —— Ensure that the average water production of each membrane element is less than 1 ton / hour
　　◆ Product water backpressure —— Calculate the product water backpressure appropriately based on the product water transportation conditions
　　◆ Years of operation —— At least simulate 3 years of operation to ensure the reliability and redundancy of the high-pressure pump selection, so that the operating life of the reverse osmosis can be extended
　　Ignoring 6 key points can easily lead to more serious failures and adverse effects
　　◆ As the operating life of the reverse osmosis system increases and the water temperature changes, when the high-pressure pump reaches its full output, the water production still cannot reach the initial design value
　　◆ The higher pressure on the product water side causes the high-pressure pump to reach its full output, but the water production still cannot reach the initial design value
　　◆ The number of membrane elements configured in the reverse osmosis is small, so as the operating life increases, higher inlet pressure is required to maintain a stable water production  
　　◆ The reverse osmosis recovery rate exceeds the normal value, and the pollution rate increases  
　　(2) Installation and commissioning stage
　　◆ Security filter —— Strictly control the tightness and compaction of the security filter cartridge installation
　　◆ Instruments and meters —— The flow sensor should keep the inlet 1.5 meter, outlet 1 meter, and equipped with a saddle-shaped sensor base
　　◆ Rinsing pipeline system —— When rinsing the system pipeline, install the security filter cartridge to prevent large particles from accumulating on the reverse osmosis equipment and its related pipelines  
　　◆ Membrane installation —— Medical glycerin should be used when installing membrane elements, and the use of detergents and other lubricants should be avoided as much as possible  
　　◆ Scale inhibitor addition —— During initial commissioning, ensure the normal addition of scale inhibitors and other chemicals to prevent membrane element contamination and scaling after prolonged commissioning time  
　　◆ Brine seal —— Check the installation direction of the brine seal when installing membrane elements  
　　◆ Pollution index SDI—— Test system inflow SDI value should be kept within 3以内
　　Ignoring 7 key points can easily lead to more serious failures and adverse effects
　　◆ Severe mechanical blockage, especially membrane elements are easily scratched by sharp impurities  
　　◆ Unstable flow meter readings, unable to play a monitoring role  
　　◆ O Wear and tear of O-rings and brine seals, resulting in decreased product water quality and high recovery rate  
　　◆ Large pressure difference causes the membrane element to produce a telescope effect, including a section of abnormal pressure difference caused by scaling and blockage
　　(3) Operation and maintenance stage
　　◆ Instruments and meters —— Regular calibration of flow meters and regular cleaning of probes
　　◆ Pressure gauge —— Regular calibration of pressure gauges
◆ Pressure vessel —— Correct Removal and Installation of Pressure Vessel End Plates
　　◆ Concentrate Water Stop Ring —— Correct Placement of Concentrate Water Stop Ring  
　　◆ Upper Limit of Operating Data —— Determine the upper limit of operating parameters, such as the pressure difference between sections, and take timely action when the upper limit is reached.  
　　◆ Manual Cleaning —— For severe mechanical blockages, avoid using excessively strong water jets for cleaning.  
　　Ignoring 6 key points can easily lead to more serious failures and adverse effects  
　　◆ High recovery rate due to the reverse installation of the brine seal ring  
　　◆ High recovery rate operation due to the overlap or partial overlap of the pressure vessel thrust ring and the concentrate outlet  
　　◆ Mixing new and old membrane elements or different types of membrane elements accelerates the rate of fouling.  
　　◆ Flow meter readings are too high or too low, affecting the adjustment of system recovery rate.  
　　◆ Excessive pressure difference causes the membrane elements to be mechanically fractured, resulting in irreversible losses.  
　　◆ Inaccurate operating pressure easily causes the system to operate under overload, accelerating the fouling rate.  
　　5 Chemical Cleaning and Sterilization  
　　Chemical cleaning and maintenance are fundamental means for restoring the performance of reverse osmosis systems after performance degradation. Therefore, both the cleaning principles and the cleaning process must match the actual on-site conditions.  
　　In addition to having a good cleaning plan, a relatively complete cleaning system is also the key to restoring the performance of the reverse osmosis system.
　　(1) Chemical Cleaning Principles  
　　◆ Multi-stage systems can be cleaned in series when the pollution is not serious.  
　　◆ Multi-stage systems must be cleaned section by section when the pollution is serious.  
　　◆ If the turbidity of the cleaning solution is too high, the medicine needs to be re-prepared for cleaning.  
　　◆ During the initial cleaning process, some concentrate water should be discharged to prevent the cleaning solution from being diluted.  
　　(2) Essential features of a chemical cleaning system 8 functions  
　　◆ Heating —— Electric heating, steam heating or hot water mixed heating  
　　◆ Reagent circulation pipeline —— The reagent is mixed evenly through its own circulation before entering the reverse osmosis device.  
　　◆ Cleaning flow meter —— Observe the changes in cleaning flow rate and adjust the cleaning operation in real time.  
　　◆ Cleaning pressure —— Observe the changes in cleaning pressure and adjust the cleaning operation in real time.  
　　◆ Cleaning pump and lift —— At least ensure that each container has 9 ton / hours of cleaning flow rate ( According to the number of pressure vessels in one section multiplied by 9 Calculation ) Heating
　　◆ Cleaning pipeline —— Relatively ample chemical cleaning pipeline diameter, ensuring that the flow rate is less than 2m/S的流速 
　　◆ Cleaning chemical tank —— Relatively ample cleaning volume  
　　◆ Cleaning security filter —— Prevent pollutants from transferring during cleaning, causing more serious blockage