What Is Ultrafiltration (UF) and How Does It Work in Water Treatment?

Water may contain suspended solids, bacteria, viruses, colloids, etc. as contaminants. More than one treatment step is generally needed to remove these contaminants. Ultrafiltration (UF) is a membrane separation process that is commonly applied in the modern water treatment systems for fine physical separation.

So, what is UF and how does it work?

Hollow fiber membranes are the membranes used by a UF system, and they have very small pores. The membrane allows water to pass through while retaining larger contaminants. UF can be used for surface water, groundwater, potable water, process water, and effluent polishing.

A water treatment system supplier will help explain the use of UF and when it can be used with other treatment methods when comparing processes.

What Is Ultrafiltration in Water Treatment?

A membrane separation process based primarily on size exclusion is called ultrafiltration. The water is pushed through the membrane, and materials that are too large to pass through are retained.

Hollow fiber is a membrane that is typically adopted in UF systems. These membranes create a barrier between larger particles and microorganisms and the water. For instance, in the published UF information from QILEE, the pore range of hollow-fiber membranes is approximately 0.03–0.05 μm.

The separation barrier in UF is a membrane, as opposed to conventional filtration, which is based on a matrix like sand or other filter media. This will be helpful if a finer degree of filtration is required for water.

How Does an Ultrafiltration System Work?

The basic cycle of operation for a UF system is essentially the same, although there are some different designs.

1. Feed Water Enters the System

Water enters the system through feeds.

The UF system receives raw water, which has been subjected to any pretreatment as may be necessary. The type of pretreatment will vary based on the source water and the overall treatment process.

2. Water Passes Through the UF Membrane

In the filtration process, water is pushed through the hollow fiber membranes by the under pressure. Larger contaminants are retained by the membrane while treated water is flowing through it.

Inside-out configuration: Water is moving in through fibers, through the membrane walls. The membrane can retain bacteria and, depending on the membrane and operating conditions, may also reject viruses while allowing treated water to pass through.

3. Treated Water Is Collected

The filtered water is collected as water stored within the membrane. It may be applied directly or to a second treatment stage, depending on the application.

For instance, UF is installed in front of RO if further treatment is required.

4. The Membrane Is Backwashed

Solids can get deposited and will have to be removed to maintain the membrane function.

Backwashing – filtered water is returned into the membrane to help with the removal of trapped solids.

What Does Ultrafiltration Remove From Water?

The main utility of UF is for physically removable contaminants. These can be suspended material, colloids, bacteria, or viruses.

UF is not a process that will remove all dissolved material from water. If dissolved salts or higher-purity water is a concern, another process may need to be performed, such as reverse osmosis.

Where Is Ultrafiltration Used?

The applications of UF depend on the source water and the purpose of water treatment.

Common applications include:

• Surface water treatment
• Groundwater treatmentx
• Potable water production
• Industrial process water
• Effluent polishing
• Pretreatment for RO systems

The same UF configuration will not necessarily be suitable for every application. System design is affected by feed-water quality, treatment capacity, and the need for the final water quality.

What Is the Difference Between UF and RO?

Both are membrane technologies, but they separate different things.

The main use of UF is for suspended materials, colloids, bacteria and viruses, etc. and RO is normally used to get a tighter separation and often to remove smaller items such as dissolved salts.

How UF and RO work well together. The feed water to the RO system can be pretreated by UF to prepare the water for subsequent RO treatment.

For example, the QILEE process water treatment system is a combination of multimedia filtration, UF, RO and mixed-bed deionization to produce high quality process water and boiler feed water.

So the key here is, UF and RO are not mutually exclusive. They may be able to do various tasks in the same treatment system.

How Do You Choose an Ultrafiltration Water Treatment System?

The first step to choosing a UF system is to identify the water and treatment goal. Not all the same system will work for all water sources.

Key factors include:

Surface water, ground water and industrial water could be different in nature.

Required capacity: The system needs to be equal to the required flow and daily water production.

The final use dictates whether the use of UF is sufficient or whether it needs to be combined with another process.

Pretreatment: Water quality before it goes into the membrane has an impact on membrane operation and maintenance.

System configurations: UF can be installed in modular, container or integrated systems.

It can be helpful to work with a water treatment system manufacturer who has the experience to design the order of treatment processes and equipment configuration that is required to treat a specific water treatment need.

When Is a Custom Water Treatment System Needed?

If the water quality and capacity requirements are simple, a typical treatment system can be used. For more complex projects, a custom water treatment system can be designed based on the water source, production, site conditions, and end product water quality.

Custom doesn't have to be all about new technology. It may just be putting the effective treatment phases in the proper sequence.

This is especially valuable when UF is used in conjunction with RO or other processes or pretreatment. Modular and containerized systems can simplify the ability to modify treatment equipment to suit site-specific needs.

Conclusion

Ultrafiltration is a membrane process used for fine physical separation of suspended solids, colloids, bacteria, viruses, and other larger contaminants. The process is simple: water flows through a hollow-fiber membrane, the contaminants are left behind, the treated water is collected, and the membrane is backwashed from time to time.

But UF is not the answer to all water quality issues. It can be used in the primary filtration stage or in combination with other filtration technologies, like RO, if stricter requirements are set for further treatment.

The most important principle for any water treatment system supplier is to match the water treatment technology to the actual water source, capacity, and desired final water quality. In more complex projects a water treatment system manufacturer can assist in creating a custom water treatment system that incorporates the required treatment stages in a functional design.