What is Ultrafiltration?
Ultrafiltration is a well-known water purification process through which water is passed through a semipermeable membrane. This membrane can hold large solutes and suspended solids, which also allows smaller solutes with low molecular weight and water to move to the permeate side. It is used before reverse osmosis as a pre-treatment which removes particles and other substances that can prevent RO and eventually harm the membrane.
Ultrafiltration as Pre-treatment for Reverse Osmosis (RO)
It is seen that ultrafiltration is a very fine filter having the capability to remove very small particles. As pre-treatment for water purification, ultrafiltration is seen to eliminate almost 90% of the contaminants having large molecule size in the given solution while operating at low pressure as well. It also helps to remove bacteria and most viruses. Not only this, but it also retains minerals in the water and gets rid of rust and harmful chemicals.
In this context, it is seen that one of the most important benefits of this method is that it generates a minimum amount of waste. It is also used to recycle effluent water which makes it suitable for irrigation. Other than this, ultrafiltration has also almost replaced media filtration due to its smaller footprint and lesser RO effort.
However, the most important way through which it enhances the life of RO membranes is through the reduction of the Silt Density Index (SDI) of water. It is seen that high SDI often damages the RO membrane, which is why it is also known as the protective precursor for RO.
Types of Ultrafiltration Systems
There are various types of ultrafiltration systems, which are inside-out, outside-in, dead-end, and cross-flow.
Inside out: This flow pattern is considered appropriate for uniform hydrodynamics. It utilizes a membrane tube which helps raw water to flow and come out radially.
Outside in: With the help of this method, Total Suspended Solids (TSS) are removed from the water. In this process, water flows inward.
Dead-end flow: In this process, water flows perpendicularly so that the waste solids get stuck to the walls of the membrane on the opposite side. The dead-end flow is generally used to get rid of lower concentrations of contaminants.
Cross-flow: Water flows parallelly in this method. Even though it requires more energy, it still removes solids efficiently as the water gets pulled to the other side due to the pressure gradient.
Ultrafiltration membranes can either be polymeric or ceramic. In this context, it is seen that polymeric membranes are more cost-effective. On the other hand, ceramic membranes act as highly reliable despite the presence of corrosive chemicals. However, ceramic membranes are mostly very expensive in terms of both capital and operating costs.
It is seen that modern ultrafiltration systems involve spiral wound or hollow fiber membranes to remove colloids, suspended soils, and turbidity in water. However, there are differences between hollow fiber and spiral wound ultrafiltration membranes, which are discussed below.
Hollow fiber membranes
Hollow fiber membranes mostly look like long strands. They are very thin and flexible in character and operate in inside-out or outside-in flow concentrations so that they can come in contact with water directly and remove the contaminants. However, it must be noted that these fibers are very delicate and vulnerable to damage.
Spiral wound membranes
On the other hand, spiral wound membranes are present where the feed travels through the flow channels tangentially across the length of the element. These membranes are considered more robust than the hollow fiber membranes.
Turbocatch Ultrafiltration by Permionics
Ultrafiltration can be considered a crucial part of water purification and wastewater recycling. However, in many cases, hollow fibers are delicate and prone to breakage, thus increasing the risk of irreversible fouling and reduced productivity. That is why Permionics has developed the Turbocatch UF System, which helps to overcome these major problems.
The Turbocatch UF System works as an alternative to hollow fibers. It has also been tried and tested on surface water, effluents, and STP outlets, which has provided excellent results.
Conclusion
Ultrafiltration is essential for clean water and wastewater treatment, removing contaminants while protecting reverse osmosis membranes. With various filtration methods available, it ensures efficient purification and minimal waste. Innovations like the Turbocatch UF System by Permionics further enhance reliability, making ultrafiltration a key solution for sustainable water management.
