The role of Ultrafiltration in water and wastewater treatment

Ultrafiltration is a well-known water purification process wherein water is passed through a semi-permeable membrane. The membrane holds large solutes and suspended solids while allowing smaller solutes with low molecular weight and water to move to the permeate side.

This technique is used before reverse osmosis as pre-treatment to remove particulates and other substances that can deter RO and harm the membrane.

Ultrafiltration pre-treatment process for water and effluents 

Ultrafiltration is a very fine filter that has the capability to remove very small particles. As pre-treatment for water purification, it eliminates 90% of the contaminants with high molecule size in the given solution while operating at low pressure. It also removes bacteria and most viruses. It also retains minerals in the water while getting rid of rust and harmful chemicals.

One of the biggest benefits of this method is that it generates very less amount of waste. It is also used to recycle effluent water, making it fit for irrigation.

The exact process of ultrafiltration depends on the configuration of the membrane system. A few common ones are as follows:

  • Inside out: This flow pattern is suitable for uniform hydrodynamics. It uses a membrane tube through which the raw water flows and comes out radially.
  • Outside in: This method is recommended to remove Total Suspended Solids (TSS) from the water. Water flows inward in this process.
  • Dead-end flow: Water flows perpendicularly so that the waste solids get stuck to the walls of the membrane on the opposite side. Dead-end flow is used to remove lower concentrations of contaminants.
  • Cross-flow: In this method, the water flows parallel. It requires more energy, but it efficiently removes solids as the water gets pulled to the other side due to the pressure gradient.

Ultrafiltration membranes may be polymeric or ceramic. Polymeric membranes are more cost-effective, while ceramic membranes are highly reliable even in the presence of corrosive chemicals. However, ceramic membranes are very expensive in terms of both capital cost & operating cost

Removal of suspended solids, turbidity, and colloids through ultrafiltration

Modern ultrafiltration systems make use of Spiral wound or hollow fibre membranes to get rid of colloids, suspended solids, and turbidity in water. 

Hollow fibre membranes look like long strands. They are very thin and flexible, operating in inside-out or outside-in flow concentrations to come in contact with water directly and remove the contaminants. One thing to note here is that these fibres are delicate and vulnerable to damage. 

Spiral wound membranes are present where the feed travels through the flow channels tangentially across the length of the element. These are more robust as compared to hollow fibre membranes.  

Clarification of feed stream by ultrafiltration to enhance life and productivity of RO

As discussed above, ultrafiltration is a pre-treatment step carried out before RO. It is now a standard method that gets rid of contaminants that would otherwise harm the RO membrane. 

Ultrafiltration has almost completely replaced media filtration because it has a much smaller footprint and requires lesser RO effort. But, the most significant way in which it enhances the life of RO membranes is by reducing the Silt Density Index (SDI) of water. High SDI often damages the RO membrane. Thus, it can also be labelled as a protective pre-cursor for RO.

Turbocatch  by Permionics – Boosting the efficiency of ultrafiltration

Ultrafiltration is a critical part of water purification and wastewater recycling. However, the hollow fibers are delicate and susceptible to breakage. This increases the risk of irreversible fouling and reduced productivity. To overcome these major problems, Permionics has developed the Turbocatch UF System.

The Turbocatch UF System serves as an alternative to hollow fibres. It has been tried and tested on surface water, effluents, and STP outlets with outstanding results. Turbocatch spiral UF solution has been much tighter in its cut off as compared to any hollow fibre membrane UF. It efficiently removes suspended solids and turbidity and also helps in removal of macromolecules,  which hollow fibre UF fails remove. It has high thermal and chemical stability, along with great chlorine tolerance and solvent resistance. When used in combination with Permionics’ revolutionary NF or RO systems, industrial effluents can be converted into into utility water which can be used for boiler, cooling tower, washing & CIP applications.

To know more about Turbocatch, please visit our website.

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