Consideration of Reverse Osmosis (RO) Use for Household Water Treatment with TDS Above 2000 or Higher

Reverse Osmosis (RO) has become one of the popular water treatment methods to produce high-quality drinking water. This technology is capable of removing a wide range of contaminants, including dissolved salts, microorganisms, and even microplastics. However, the use of RO for water with extremely high TDS requires special consideration and careful planning.

Understanding Total Dissolved Solids (TDS) and its Implications

Total Dissolved Solids (TDS) is a measure of the total amount of dissolved substances in water, including minerals, salts, metals, and other dissolved cations and anions. Water with high TDS usually has an unpleasant taste and can cause problems in household appliances such as water boilers, washing machines, and water pipes. The World Health Organization (WHO) recommends that drinking water should have a TDS below 600 ppm, although the maximum acceptable limit is 1000 ppm.

When raw water TDS reaches 2000 ppm or more, it indicates a very high level of contamination. Water with this high TDS may come from wells that have been contaminated with seawater (seawater intrusion) or surface water sources polluted with industrial and domestic effluents. In some areas in North Jakarta, for example, seawater intrusion has caused a significant increase in TDS in groundwater.

Water Treatment Challenges with High TDS

Treating water with TDS above 2000 ppm presents several challenges:

1. Lower RO system efficiency: The higher the raw water TDS, the greater the pressure required for the RO process, which translates to higher energy consumption and lower efficiency.
2. Potential scaling.
3. Higher scaling potential: High mineral concentrations can lead to scale formation (scaling) on RO membranes, which reduces membrane performance and lifespan.
4. Potential for higher scaling.
5. More intensive pretreatment needs: Water with high TDS may require more complex pretreatment stages to protect the RO membranes.
6. More intensive pretreatment requirements.
7. More wastewater production: RO systems that treat water with high TDS tend to produce more reject water.
8. More wastewater production.

Water Treatment Solution for Households

To solve the problem of high TDS water, several approaches can be considered:

1. Whole House Water Treatment System

This system is designed to treat the entire water supply entering the home. The main components of this system include:

• Raw water storage tank (from municipal water source or well)

• Distribution pump
• Mechanical filter to remove coarse particles
• Water softener system to reduce hardness
• Activated carbon filter to remove chlorine and odor
• Ro system to reduce TDS
• Disinfection system (UV or chlorination) to ensure bacteria-free water

For homes with limited access to municipal water or looking to save costs, the use of well water may be an option. However, well water often contains high levels of iron and bacteria. In these cases, the use of manganese greensand or birm filters can help remove iron. If iron levels are low, the use of a direct water softener is also possible.

Pressure vessels such as FRP tanks from Pentair or the more economical Hydropro FRP tanks are commonly used in filtration systems. Additionally, Wellmate pressure tanks can be used to ensure the pump does not turn on every time the tap is opened, helping to maintain a steady water pressure throughout the home.

2. Point-of-Use (POU) RO system

For households that do not require whole-house water treatment, a point-of-use RO system can be a more affordable solution. These systems are typically installed under the kitchen sink and provide high-quality drinking water through a separate faucet.

One example of an effective POU RO system is the Pentair Merlin Undersink Reverse Osmosis. This system is specifically designed to cope with water with high TDS and can produce high-quality drinking water.

3. Whole House RO System

For luxury homes or situations where water quality is very poor, a whole house RO system can be an option. Although more expensive, this system guarantees consistent water quality throughout the house. These systems usually consist of:

• Extensive pretreatment (filtration, softening, iron removal)
• Large capacity RO system
• Treated water storage tank
• Post-treatment system (remineralization, UV disinfection)

For a whole house RO system, the use of high-quality RO membranes is essential. Membranes such as DuPont FilmTec for brackish water or CSM membranes for brackish water can be a good choice to tackle water with high TDS.

Special Considerations for Very High TDS Water

When dealing with water with TDS above 2000 ppm, some additional considerations need to be taken into account:

1. Long-term Planning

It is important to consider the possibility of future TDS increases, especially if the water source is a well that has experienced seawater intrusion. A system designed to handle the current 4000 ppm TDS may need to be upgraded in a few years if the TDS continues to increase to 8000 ppm or more.

2. Multi-stage RO system

For water with very high TDS, a two-pass RO system may be required. In this system, the treated water from the first stage is passed back through a second set of RO membranes to achieve a higher level of purity.

As explained in the technical literature, "In a two-stage RO system, permeate water from the first stage is fed as raw water to the second stage. This allows achieving higher water quality by passing the water through two sets of RO membrane elements."

3. Extensive Pretreatment

Water with very high TDS may contain high concentrations of contaminants such as iron, manganese, or silica that can damage RO membranes. Proper pretreatment is essential to protect the RO system's investment.

The use of specialized filtration media such as Inversand Manganese Greensand or Clack Birm can help remove iron and manganese before the water enters the RO system.

4. Proper Membrane Selection

For water with very high TDS, proper RO membrane selection is crucial. Specialized membranes for brackish water or even membranes for seawater may be required. Membranes like Toray for brackish water or DuPont FilmTec for seawater can be a good choice for this situation.

5. Wastewater Management

An RO system that treats water with very high TDS will generate significant volumes of reject water. Good planning for the management and disposal of this wastewater is essential, especially in areas with limited drainage.

Implementation of RO System for High TDS Water

The following are general steps in implementing an RO system for high TDS water:

1. Analyze water quality: Conduct a thorough test of the water source to determine not only TDS, but also other parameters such as hardness, iron, manganese, silica, and other contaminants.
2. System design.
3. System design: Based on the water analysis results, design a suitable treatment system, including pretreatment, RO, and post-treatment stages.
4. System design.
5. Component selection: Select high-quality components that are suitable for local water conditions. This includes the selection of RO membranes, high pressure pumps, and control systems.
6. Component selection: Select high-quality components that are suitable for local water conditions.
7. Installation: Ensure that the system is installed by experienced technicians and in accordance with industry standards.

1. Installation.
2. Testing and commissioning: Perform thorough testing to ensure the system is operating to specification.
3. Testing and commissioning.
4. Operator training: Provide adequate training to system users or operators to ensure proper operation and maintenance.
5. Operator training.
6. Routine monitoring and maintenance: Establish a routine monitoring and maintenance schedule to ensure optimal system performance and extend the life of its components.

Read more:

Sea Water Treatment Into Drinking Water: Steps and Technology

Sea Water Treatment to Drinking Water.

Challenges and Solutions in Operating an RO System for High TDS Water

Operating an RO system for water with high TDS has some special challenges:

1. High Energy Consumption

Challenge: RO systems for water with high TDS require higher operating pressures, which translates to greater energy consumption.

Solution: Consider the use of high-efficiency pumps such as Flint and Walling RO pumps designed specifically for RO applications. Additionally, implementation of an energy recovery system can help reduce overall electricity consumption.

2. Membrane Fouling and Scaling

Challenges: Water with high TDS has a greater potential to cause fouling (clogging) and scaling (mineral deposition) on RO membranes.

Solution: Implement an effective pretreatment system, including water softening and iron/manganese removal. Use appropriate antiscalants and consider using fouling-resistant RO membranes. Perform regular membrane cleaning as per manufacturer's recommendations.

3. Fluctuating Permeate Quality

Challenge: Fluctuations in raw water quality can lead to variations in the quality of treated water (permeate)

Solution: Implement an automated monitoring and control system to adjust RO system operating parameters based on changes in raw water quality. Use of analyzer pH and conductivity Create can help in real-time monitoring of water quality.

4. High Wastewater Production

Challenge: RO systems that treat water with high TDS tend to produce larger volumes of reject water.

Solution: Consider implementation of a wastewater recovery system or reuse of wastewater for non-consumption applications. In some cases, multi-stage RO systems can help improve water use efficiency.

5. Need for More Frequent Membrane Replacement

Challenge: RO membranes used to treat water with high TDS may require more frequent replacement due to heavier workloads.

Solution: Invest in high-quality membranes such as Xelect ULP and XLP RO membranes that are designed for high durability. Perform regular preventive maintenance and monitor membrane performance to optimize replacement time.

Conclusion

The use of Reverse Osmosis (RO) technology for domestic water treatment with TDS above 2000 ppm or higher is an effective solution, but requires careful planning and consideration. A well-designed RO system can produce high quality water even from highly polluted water sources, but it is important to consider factors such as proper pretreatment, selection of suitable components, and wastewater management.

In its implementation, it is important to consider factors such as appropriate pretreatment, selection of suitable components, and wastewater management.

In its implementation, it is important to involve experts in the design and installation of the system, as well as ensuring proper regular maintenance. With a comprehensive approach, RO systems can be a long-term solution to the problem of high TDS water, providing access to clean and safe water for households in areas with significant water quality challenges.

With a comprehensive approach, RO systems can be a long-term solution to the problem of high TDS water, providing access to clean and safe water for households in areas with significant water quality challenges.

In closing, it is worth remembering that water treatment technology is constantly evolving. Innovations in membrane design, control systems, and pretreatment methods continue to emerge, offering more efficient and effective solutions to the challenges of high TDS water. Therefore, it is important for users and practitioners in the field of water treatment to constantly update their knowledge and keep up with the latest developments in RO technology and water treatment in general.

Questions and Answers

1. Are RO systems effective for removing microplastics from water?

Yes, Reverse Osmosis (RO) systems are very effective in removing microplastics from water. RO membranes have very small pores, typically around 0.0001 microns in size, while microplastics are generally between 1 micron to 5 millimeters in size. Therefore, RO membranes can easily retain microplastic particles, preventing them from passing through the membrane and into the treated water. Furthermore, the prefiltration stage in the RO system also helps to remove larger particles before the water reaches the RO membrane, thus increasing the overall effectiveness of the system in removing microplastics.

2. How to solve the scaling problem on RO membranes when treating water with high TDS?

To solve the scaling problem in RO membranes when treating water with high TDS, several steps can be taken:

1. Effective pretreatment: Implement a water softening or ion exchange system to reduce hardness before the water enters the RO system.
2. Effective pretreatment.
3. Use of antiscalants: Add appropriate antiscalant chemicals to the feed water to prevent scale formation on the membranes.
4. Antiscalant utilization.
5. Recovery rate optimization: Set the RO system's recovery rate at an optimal level to reduce the concentration of minerals that can cause scaling.
6. Regular membrane cleaning: Perform membrane cleaning as per the recommended schedule using appropriate cleaning agents.
7. Monitoring and control of RO system.
8. PH monitoring and control: Keep the feed water pH within an optimal range to reduce the potential for scaling.
9. Monitoring and control of pH.
10. Use of anti-fouling membranes: Choose RO membranes specifically designed for resistance to scaling and fouling.
11. Use anti-fouling membranes.

3. Are there alternatives to RO for treating water with very high TDS for domestic use?

Yes, there are several alternatives to RO for treating water with very high TDS for domestic use, although RO remains one of the most effective methods. Some of these alternatives include:

1. Distillation: This process involves boiling water and collecting the condensed vapor, effectively removing almost all contaminants including high TDS.
2. Distillation.
3. Electrodialysis: This technology uses electric current and ion-selective membranes to separate dissolved salts and minerals from water.
4. Electrodialysis.
5. Ion exchange: This method is effective for removing certain ions from water, although it may not be as effective as RO for very high TDS.
6. Ion exchange.
7. Nanofiltration: A membrane technology that has a larger pore size than RO but is still effective at reducing TDS.
8. Nanofiltration.
9. Combination of technologies: The use of multiple technologies together, such as water softening followed by nanofiltration, can be an effective alternative.
10. Combination of technologies.

However, keep in mind that each method has its own advantages and disadvantages, and the selection of an appropriate method should be based on an analysis of the specific water quality and needs of the household.

References

1. Byrne, W. "Reverse Osmosis: A Practical Guide for Industrial Users." 2nd Edition, 2002.
2. World Health Organization. "Guidelines for Drinking-water Quality." 4th Edition, 2011.
3. American Water Works Association. "Reverse Osmosis and Nanofiltration." Manual of Water Supply Practices, M46, 2007.
4. Fritzmann.
5. Fritzmann, C., et al. "State-of-the-art of reverse osmosis desalination." Desalination, 216(1-3), 2007, pp. 1-76.
6. Greenlee, C., et al.
7. Greenlee, L.F., et al. "Reverse osmosis desalination: Water sources, technology, and today's challenges." Water Research, 43(9), 2009, pp. 2317-2348.
8. Water Research, 43(9), 2009, pp. 2317-2348.