Reverse osmosis (RO) is a water purification process that removes dissolved impurities by forcing water through a semi-permeable membrane under pressure. This membrane allows water molecules to pass while blocking larger molecules and contaminants. The process is widely used for desalination, wastewater treatment, and producing potable water.
Principle of Reverse Osmosis:
In natural osmosis, water moves from a region of low solute concentration to high solute concentration through a semi-permeable membrane, aiming to equalize concentrations on both sides. The best example of natural osmosis is the nutrients absorbed by roots of plants, nutrient absorption by human body parts after digestion.
Reverse osmosis, however, is an exactly opposite process. The higher concentration solute flows to the lower concentration, not naturally but with an application of external pressure. This pushes water from a high solute concentration to a low solute concentration, thereby separating impurities from the water. The impurities are collected on the Reverse Osmosis membrane. A typical small reverse osmosis membrane’s specification on its pore size can be define through its ability to filter ions with a specific size.
Process of Reverse Osmosis:
1. Pre-treatment: Water is pre-filtered to remove large particles and chlorine, which can damage the RO membrane.
2. Pressurization: The pre-treated water is then pumped at high pressure against the RO membrane.
3. Separation: As water molecules pass through the membrane, dissolved salts, bacteria, and other impurities are retained and flushed away.
4. Post-treatment: The purified water may undergo further treatment, such as pH adjustment or remineralization, to ensure it meets desired quality standards.
Applications of Reverse Osmosis:
• Desalination: Converting seawater into freshwater for drinking and irrigation.
• Wastewater Treatment: Removing contaminants from industrial effluents before discharge or reuse.
• Food and Beverage Industry: Purifying water for manufacturing processes to ensure product quality.
• Pharmaceuticals: Producing ultrapure water for medicinal formulations and laboratory use.
TKA in its all systems, uses Reverse Osmosis membranes with a 100 Daton Cutt Off. 100 Dalton is the ionic size which can be filtered through the membrane, thus blocking all ions with size greater than 100 Dalton.
TKA Advance Reverse Osmosis remove all kinds of impurities such as Salts, Ions, Organics, Inorganics, Bacteria, Particles, Pyrogens, etc… upto 99%. These highly efficient RO membranes reduce the load of salts on downstream technologies such as Ion Exchange, Electro-De-ionization, etc…
The amount of pressure required depends on the salt concentration of the feed water. The more concentrated the feed water, the more pressure is required to overcome the osmotic pressure.
The desalinated water that is demineralized or deionized, is called permeate (or product) water. The water stream that carries the concentrated contaminants that did not pass through the RO membrane is called the reject (or concentrate) stream.
As the feed water enters the RO membrane under pressure the water molecules pass through the semi-permeable membrane and the salts and other contaminants are not allowed to pass and are discharged through the reject stream (also known as the concentrate stream), which goes to drain or can be fed back into the feed water supply in some circumstances to be recycled through the RO system to save water. The water that makes it through the RO membrane is called permeate or product water and usually has around 95% to 99% of the dissolved salts removed from it as compared to feedwater.
To avoid build-up of contaminants, cross flow filtration allows water to sweep away contaminant build up and also allow enough turbulence to keep the membrane surface clean. This automatic cleaning can happen if the membrane has a strong cross flow over its surface. This is achieved by having a good power pump behind the membrane. The permeate flow depends on feedwater pressure exerted by pump and the temperature of water. Each degree increase in temperature of water will increase the permeate flow by 3%. Thus, if a RO membrane is “tuned” to generate 12 ltr/hour flow at 15C, if the feedwater temperature is 25C (which generally is the case in any part of India, irrespective of seasons) then the permeate flow will increase by around 30%, means a standard 12ltr/hr RO will give out approximately 15.6ltr/hr. Now if a system has EDI cell rated at 12ltr/hr, after the RO it surely can’t handle such increase in flow. Even
if it gives out bigger flow physically, the quality will be drastically reduced due to the small amount of resin contained in the EDI cell. To prevent the deterioration of water quality after EDI particularly, there is only one way. The design can be done such that the flow from RO permeate is reduced. To reduce the permeate flow the pump reduces the amount of water pumped on the membrane by reducing the voltage to the pump. Thus, the pump rotates at a smaller speed and reduces the pressure on membrane. However, this continuous adjustment is possible till water temperature remains below 30C. If temperature exceeds 30C such temperature feedback mechanism to the pump does not work as then pump will fully stop as it won’t get the bare minimum voltage to run. Hence this is a big disadvantage in tropical or Indian conditions. Further due to this continuous adjustment in the rotation speed of pump motor, the motor becomes weak and eventually fails.
Now let’s look at a differently. What happens if temperature of water reduces? It goes to 4C which is very much possible in European countries. The flow reduces from RO and inturn, from EDI, the quality of water from EDI may improve but quantity is less than the rated flow rate. The temperature feedback mechanism works here, and it increases the
voltage on the pump to keep the flow rate constant. In European countries the tap water temperature very very rarely exceeds 30C and thus the temperature feedback mechanism is perfect for European countries, not for India or tropical countries.
Now there are distinct disadvantages of this temperature feedback mechanism.
1. It is designed for European countries to increase flow, and it works well where temperature of water is below 10C.
2. For Indian conditions after 30C it won’t work and increased flow from EDI cell will still provide bigger quantity but worse water quality.
3. With this continuous varying voltage, the pump gets frequent shocks of voltage increase and decrease. This causes failure of pumps and incurs huge running costs. Which is experienced by majority users.
4. Water system is a backbone of lab. A failure of water system brings the lab to standstill and causes loss of analysis time.
5. Upgradation of such systems with EDI is highly expensive and sometimes difficult than buying an entirely new system.
What is the mechanism to prevent above?
TKA has a special design by which the control of flow is done semi-automatically. The tuning of all TKA water systems can be done at 25C instead of typical Eurpoean design of 15C. And this can be done even on site by the engineer who installs the system!! Even if the adjustment is not done on-site, TKA ion exchanger or even the EDI is capable to handle that increase efficiently without compromising on quality of water. In fact, the TKA ion exchanger cartridge in Type II is capable to tolerate the flow from 6 ltr/hr to 40 ltr/hr. Thus, TKA systems can handle feedwater irregularities efficiently and still maintain the quality of water for a longer time, consistently. Therefore it is technically safe to upgrade the system flow rate from 6 upto 40 ltr/hr with same hardware such as pump and consumable ion exchange but by simply replacing the RO membrane of a bigger size.
Advantages with the TKA design:
1. Upgradation is easy and economical. Just replace the smaller RO cartridge with bigger. Replacement of RO cartridge itself can be done even by user. Engineer is not required.
2. Save on capital cost on procurement of new system.
Introduction
Pre-filtration is a crucial step in laboratory water purification systems, ensuring that incoming water is free from particulate matter, sediments, and large contaminants before undergoing further treatment. This process enhances the efficiency and longevity of downstream purification stages, such as reverse osmosis (RO), deionization (DI), and ultrafiltration (UF).
The primary objective of pre-filtration is to remove suspended solids, organic matter, and other impurities that could interfere with sensitive laboratory applications. Pre-filtration helps in:
• Protecting delicate purification components from clogging and fouling.
• Enhancing the performance of RO membranes and DI resins.
• Reducing maintenance and operational costs by preventing early filter replacements.
• Improving overall water quality for analytical, microbiological, and chemical experiments.
1. Sediment Filters
o Typically composed of polypropylene or pleated polyester.
o Removes large particles like sand, rust, and silt (5–50 microns).
o Extends the life of finer filtration membranes.
2. Carbon Filters
o Made from activated carbon or carbon block.
o Adsorbs chlorine, organic compounds, and volatile organic compounds (VOCs).
o Protects RO membranes from chlorine degradation.
3. Depth Filters
o Constructed from layers of fibrous materials.
o Provides graded filtration, capturing progressively smaller particles.
o Effective in removing colloidal matter and biofilm precursors.
4. Prefiltered Cartridges
o Multi-stage filters that combine sediment and carbon filtration.
o Optimized for high-purity laboratory applications.
o Enhances bacterial and endotoxin removal in critical setups.
When designing a laboratory water purification system, selecting the right pre-filtration method depends on:
• Water Quality: The level of particulates, chlorine, and organic matter in the feed water.
• Application Requirements: Different experiments demand varying purity levels.
• System Compatibility: Ensuring filters align with RO or DI system specifications.
• Flow Rate and Capacity: Matching filtration capacity to laboratory water consumption needs.
Pre-filtration is an essential component of a laboratory water purification system. It ensures the removal of particulates and contaminants, enhances the efficiency of downstream processes, and prolongs the lifespan of purification equipment. By selecting the appropriate pre-filtration method, laboratories can achieve consistent water quality, reduce maintenance costs, and maintain the integrity of scientific research.
How does TKA use this technology in their systems?
TKA has a vast knowledge of design of ultrapure water purification systems. Each technology is used in TKA systems optimally as per the feedwater quality. For various geographies we procure a feedwater analysis report either from customer or analyse water at reputed NABL certified laboratories. We have numerous examples where a thorough analysis of feedwater and correct configuration of prefiltration has helped the customer in minimizing the running costs of the main system.