Comprehensive Guide To Reverse Osmosis System Maintenance

Reverse osmosis systems are a great way to purify water for various applications, be it drinking, industrial, agricultural, or medical. However, like any other equipment, reverse osmosis systems need regular maintenance to ensure their optimal performance and longevity. This is especially true for Industrial and commercial RO Systems – since without regular upkeep, their parts could malfunction and cause huge financial losses.

Badly maintained reverse osmosis systems suffer from reduced flux, increased pressure, fouling, scaling, and even microbial growth. These problems can affect the quality and quantity of the purified water, as well as increase the operating costs and risks of system failure.

In this blog, we will explain why and how to maintain your reverse osmosis water system in different scenarios. Whether you are a purchaser, engineer, technician, or supplier of water maintenance systems, you will find useful information and tips that will allow you to get the best performance from your RO System.

Figure 1 Reverse Osmosis System Maintenance

Factors Affecting RO System Performance

Several parameters affect the optimal working of an RO System. These parameters affect the fouling and scaling of the RO membrane, which reduces its permeability and efficiency. The performance of a reverse osmosis system can be affected by factors such as water usage and water flow.

Here is a table that explains how different parameters affect the maintenance of RO systems.

Parameter

Definition

Effect on RO membrane

Silt density index (SDI) A measure of the suspended particles and colloidal in the feedwater High SDI indicates a high fouling potential and reduces membrane permeability and efficiency
Differential pressure The difference between the pressure of the input (feed pressure) and the pressure of the output (permeate pressure) High differential pressure indicates high fouling or scaling of the membrane and reduces membrane performance
Normalized permeate flow The actual permeate flow divided by the design permeate flow Low normalized permeate flow indicates low membrane productivity and may be caused by fouling, scaling, or damage
Percent rejection The percentage of dissolved solids that are rejected by the membrane Low percent rejection indicates low membrane selectivity and may be caused by fouling, scaling, damage, or incorrect operation
Pressure drop coefficient A factor that relates the pressure drop across a membrane element to the flow rate A high-pressure drop coefficient indicates high resistance to flow and may be caused by fouling, scaling, or damage

But this list is not exhaustive. There are different industrial and commercial RO systems and they have different parameters that affect their performance. For example, brackish water reverse osmosis systems are designed to treat water with higher levels of salinity and can be affected by factors such as water temperature and pressure. If your RO system has given up the ghost, you can contact NEWater for top-quality systems that suit your needs.

Understanding RO Membrane Cleaning

RO membranes are the most delicate part of the RO water system. They do most of the filtering and are prone to fouling and scaling by various contaminants and deposits that can reduce their performance and lifespan. Therefore, regular and effective cleaning of RO membranes is essential to maintain optimal operation and water quality. Here is a detailed list of the common contaminants that plague RO membranes and how to remove them.

A. Common Contaminants and Deposits

The pre-filter and sediment filter help to remove common contaminants and deposits from the water before it reaches the reverse osmosis membrane. Some of the common contaminants and deposits that can foul or scale RO membranes are:

Organic Matter: These include natural organic matter (NOM), humic substances, oils, greases, proteins, sugars, etc. that can adhere to the membrane surface and cause biofilm formation, increased pressure drop, reduced permeate flux, and salt rejection.

Silt: This refers to fine particles of clay, sand, dust, etc. that can clog the membrane pores and increase the hydraulic resistance and pressure drop across the membrane.

Microbiological accumulations: These include bacteria, algae, fungi, etc. that can grow on the membrane surface and form biofilms that reduce permeate flux and quality, increase pressure drop, and cause corrosion and odors.

Scaling materials: These include calcium carbonate, calcium sulfate, barium sulfate, strontium sulfate, silica, iron, etc. that can precipitate on the membrane surface and reduce permeate flux and salt rejection, increase pressure drop, and damage the membrane structure.

Figure 2 Scaling materials

B. Cleaning Methods for RO Membrane

There are two main methods for cleaning RO membranes: the dilution method and the soaking method.

1. Dilution method for regular cleaning

The dilution method involves circulating a cleaning solution through the reverse osmosis(RO) system at a low pressure and high flow rate for a certain period of time. The cleaning solution is usually a mixture of water and a chemical cleaner that can dissolve or disperse the contaminants and deposits on the membrane surface. The chemical cleaner can be either acidic or alkaline depending on the type of fouling or scaling material. The dilution method is suitable for regular cleaning of RO membranes that are not severely contaminated or scaled.

The following general steps can be followed for the dilution method:

  • Inspect the cleaning tank, hoses, and cartridge filters. Clean them if necessary and install new cartridge filters.
  • Once the inspection is done, completely fill the cleaning tank with either reverse membrane permeate or deionized water. Then turn on the agitator or tank recirculation pump to allow the RO permeate or deionized water to get mixed properly.
  • Gradually pour the chosen cleaning agent into the tank according to the required product concentration and the total amount of liquid. Allow it to mix thoroughly.
  • Check the solution temperature and pH. Adjust them if necessary according to the manufacturer’s recommendation or contact Complete Water Solutions for guidance.
  • Circulate the cleaning solution through the RO water system at a low pressure (usually less than 50 psi) and high flow rate (usually 10-15% of normal permeate flow) for a certain period of time (usually 30-60 minutes). Monitor the pressure drop, pH, temperature, conductivity, and turbidity of the solution during circulation.
  • Drain the cleaning solution from the RO system and flush it with RO permeate or deionized water until the pH, conductivity, and turbidity return to normal levels.

2. Soaking method for severe contamination

The soaking method involves filling the RO system with a cleaning solution and letting it soak for a certain period of time without circulation. The cleaning solution is usually a mixture of water and a chemical cleaner that can dissolve or disperse the contaminants and deposits on the membrane surface. The chemical cleaner can be either acidic or alkaline depending on the type of fouling or scaling material. The soaking method is suitable for severe cleaning of RO membranes that are heavily contaminated or scaled.

Figure 3 Soaking method on RO system

The following general steps can be followed for the soaking method:

  • Inspect the cleaning tank, hoses, and cartridge filters. Clean them if necessary and install new cartridge filters.
  • Once the inspection is done, completely fill the cleaning tank with either reverse membrane permeate or deionized water. Then turn on the agitator or tank recirculation pump to allow the RO permeate or deionized water to get mixed properly.
  • Check the solution temperature and pH. Adjust them if necessary according to the manufacturer’s recommendation or contact Complete Water Solutions for guidance.
  • Fill the RO system with the cleaning solution at a low pressure (usually less than 50 psi) until it reaches all parts of the system. Close all valves and isolate the system from any external sources of water or air.
  • Let the cleaning solution soak in the RO system for a certain period of time (usually 4-8 hours). Monitor the pressure drop, pH, temperature, conductivity, and turbidity of the solution during soaking.
  • Drain the cleaning solution from the RO system and flush it with RO permeate or deionized water until the pH, conductivity, and turbidity return to normal levels.

Note: Importance of minimizing chemical contact time

It is important to minimize the contact time between the chemical cleaners and the RO membranes to avoid damaging them. Chemical cleaners can degrade the membrane structure or cause irreversible changes in its properties if they are left in contact with it for too long. Therefore, it is recommended to follow the manufacturer’s instructions or contact Complete Water Solutions for guidance on how long to circulate or soak the cleaning solution in the RO system. It is also advisable to rinse the RO system thoroughly with water after each cleaning cycle to remove any residual chemicals from the membrane surface.

Normalization – Compare Your RO System’s Performance to the Standard

When you install new membrane elements in your system, you should record their performance data, such as flows and quality parameters. You can refer to these values as the ‘normal values’. This will help you monitor how well your membranes are working over time. Before starting maintenance, you should compare your RO System’s readings to the ‘normal’ values. This will help you understand whether your RO system is performing optimally or not. This is called normalization.

Normalization is like putting your current data in a time machine and taking them back to the day you started your system. Then you can see if your membranes are still performing as well as they did on the first day. If not, you may need to do some maintenance, such as cleaning your membranes or changing some settings.

Safety Guidelines for Operating and Maintaining Reverse Osmosis Membrane Systems

Both external and internal factors play a huge role in the performance of a Reverse-Osmosis System. These include the following:

1. Temperature Control

Maintaining proper temperature is essential for safe operation. Elevated water temperatures can lead to concentration polarization, causing scaling issues. Additionally, higher temperatures increase ion solubility in water, which can result in membrane failure. Therefore, it is important to operate within the designated temperature range and consider measures to reduce the inlet water temperature when necessary.

Figure 4 Maintaining proper temperature for RO system

2. pH Control

The pH value of the feedwater significantly affects scaling in the RO membrane system. The Langelier Index (LSI) is commonly used as a reference. A negative LSI indicates a higher likelihood of corrosion than scaling, while a positive LSI suggests the opposite. In the case of reverse osmosis concentrate water, the empirical LSI value is 0.2.

3. Redox Potential (ORP)

ORP serves as a crucial control parameter, reflecting the oxidant content in the feed water. It is essential to maintain a low range of oxidant content in the influent water to prevent membrane damage. Typically, the residual chlorine content should be controlled below 0.1 ppm.

4. Antiscalant Usage

To mitigate membrane scaling, it is necessary to add scale inhibitors during the operation of the RO membrane system. The recommended content of scale inhibitors in the feed water is generally controlled between 3 and 5 ppm.

By adhering to these guidelines, suppliers, engineers, and purchasers can ensure the safe operation and maintenance of reverse osmosis membrane systems. Implementing strict control over various parameters and conducting routine maintenance procedures will help optimize performance and prolong the lifespan of these essential water treatment systems.

Specific Cleaning Procedures for Different Deposits

  • Calcium Carbonate Scaling: To clean calcium carbonate scaling from an RO membrane, you can prepare a cleaning solution and introduce it into the system. Keep circulating the cleaning liquid for 10 minutes or until the color stops changing. Leave the elements submerged in the cleaning liquid for a short time if they have little scaling, and for a longer time if they have a lot of scaling. Proceed with high-flow pumping and flush out.
  • Calcium Sulfate Scaling: This happens when calcium sulfate builds up on the filters. To clean it, you need to use the right cleaning agents such as tetra potassium ethylenediaminetetraacetate with potassium carbonate, and adjust the pH.
  • Metal Oxide Scaling: This happens when metal oxides build up on the filters. To clean it, you need to use a method that’s similar to cleaning calcium carbonate scaling. One method is using a pickling solution of 10 to 15% nitric acid plus 1 to 3% hydrofluoric acid.
  • Organic Deposits: This happens when organic matter builds up on the filters. To clean it, you need to use the right cleaning agents such as an alkaline cleaner for removing non-petroleum organic soils and adjusting the pH. If the contamination is severe, you can use the soaking method.

Troubleshooting and Fault Analysis

Once you are done with your RO System’s maintenance, some small issues might still arise. In this case, it is important for you to know what to do. Here are the rubrics you should follow in this case:

1. Understanding RO System Operation, and Principles: Learn how your water system works and what it’s supposed to do. Learn about the design principles of the reverse osmosis (RO) System.

2. Identifying Symptoms of System Malfunction: Look for signs that your water system isn’t working right.

3. Steps for Problem Identification and Analysis: Follow these steps to figure out what’s wrong:

  • Verification and calibration of instruments: Make sure your tools are working right.
  • Examination of operational data: Look at the data to see if anything is off.
  • Evaluation of mechanical and chemical issues: Check for problems with the machine or the chemicals.
  • Analysis of feedwater chemistry changes: See if the water has changed in any way.
  • Identification and analysis of contaminants: Look for anything that shouldn’t be in the water.

Figure 5 Identification and analysis of contaminants for RO system

Effective Maintenance Measures

It is pertinent to follow safety guidelines when operating and maintaining a reverse osmosis system, including proper handling of the storage tank and delicate RO membrane. Regular filter replacement and proper maintenance of the reverse osmosis membrane can help ensure that it only needs to be replaced when necessary. If you are looking for general measures for the RO system’s maintenance, here are 6 measures that summarize it all.

1. Importance of Regular Verification and Calibration: Make sure your tools are working right by checking them often. For the best-quality parts of an RO water system, NEWater is your best bet. NEWater is the market leader when it comes to parts and accessories for water treatment systems.

2. Analyzing Operational Data for Performance Evaluation: Look at the data to see how well your water system is working.

3. Addressing Mechanical and Chemical Issues: Fix any problems with the machine or the chemicals.

4. Assessing Feedwater Chemistry Changes: See if the water has changed.

5. Identifying and Analyzing Contaminants: Look for anything that shouldn’t be in the water.

6. Selecting Appropriate Cleaning Methods: Choose the right way to clean your water system.

7. Implementing Chemical Cleaning and Disinfection Techniques: Use chemicals to clean and disinfect your water system. Regular filter replacement and proper maintenance of the reverse osmosis membrane can help ensure that it only needs to be replaced when necessary.

Conclusion

All in all, regular maintenance is essential for ensuring the longevity and effectiveness of your reverse osmosis system. We have listed the steps you need to follow if you are planning on doing this yourself. If you need further advice and assistance, please contact our engineers at NEWaters. With more than 20 years of experience in the water treatment industry, our engineers know how to get the maintenance done right.

Of course, whether you choose to do it yourself or consult a water treatment company for help, make sure to follow a regular maintenance schedule and pay attention to any signs that indicate your system needs attention. By doing so, you can enjoy clean and safe drinking water for years to come.

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