Basics of Ultrafiltration: An Industrial Water Filter System Guide

Ultrafiltration technology plays an important role in industrial water treatment projects. Compared to traditional filter media filtration, this water treatment technology uses ultrafiltration membranes for higher filtration accuracy, effectively removing not just bacteria, viruses, and macromolecular organic matter, but also colloids and other particulates. Aside from being integral to wastewater reuse and municipal drinking water treatments, ultrafiltration technology is also pivotal for industries ranging from power, petrochemical, metallurgy, and electronics, to food and beverage, pharmaceutical, and more. 


What is Ultrafiltration

Ultrafiltration (UF) is a water purification process in which raw water, under a driving pressure, is forced through a semipermeable membrane. Suspended solids and macromolecular impurities remain on the retentate side of the membrane, while water and low molecular weight solutes are filtered through the membrane to the permeate side. Ultrafiltration can intercept nearly all suspended solids, macromolecules, and bacteria in water, and can remove BOD and COD by 20 - 60%. This makes ultrafiltration systems a popular choice in industrial filtration as they produce stable water quality no matter what the water source is. 

Ultrafiltration VS Other Filtration Techniques

Aside from its separation characteristics, here is how Ultrafiltration differs from other filtration techniques:

1. The sieve’s aperture size is smaller, retaining almost all bacteria, heat sources, viruses, colloidal particles, proteins, and macromolecular organic matter.

2. Effective separation does not just depend on the pore size of the membrane and the size, shape and rigidity of solute particles. It also heavily relies on the solution’s chemical properties (ph, electrical) and composition (presence of other particles), as well as the surface structure of the membrane’s dense layer including its electrical and chemical properties (hydrophobic and hydrophilic, etc.).

3. The whole filtration process is carried out dynamically. There is no filter cake formation as only a few materials can’t pass through the membrane surface. The filtration rate gradually stabilizes, with filtration efficacy highly dependent on the raw feed water.

Ultrafiltration Operation Methods

When looking for ultrafiltration membrane systems for your industrial water system facility, be sure you get the right unit following the operation method your application requires. Ultrafiltration membrane systems are designed to follow different filtration processes. Here are two of the most popular operation methods you can consider:

1. Dead-End Filtration

This model, also known as Full-Filtration, is the most basic form and is similar to traditional filtration. It involves raw water entering the ultrafiltration membrane via an applied pressure and the filtered matter accumulating on the membrane’s surface. Water flows through the membrane, returning 100% permeate.

As macromolecular particles and colloidal impurities are retained on the surface of the filter it eventually becomes clogged, resulting in a decrease in flux and filtration capacity. For this reason, the membrane surface must undergo regular backwash or cleaning to maintain the membrane’s performance.

2. Cross-flow Filtration

Cross-flow filtration, also called tangential flow filtration, is an excellent method to filter liquids with higher concentrations of filterable particulates. It involves supplying constant high-velocity flow along the membrane surface to prevent accumulation of suspended solids and to increase membrane flux. Employing differences in pressure across the elements, water is then driven through the membrane to return permeate or treated water, while particles retained by the membrane become part of the concentrate that continuously pass along the membrane in a cyclic pattern.

The process is known as “cross-flow” because the feed flow and the filtration flow direction follow a 90° angle. Under the same water production rate, the energy consumption of this filtration model is higher than dead-end filtration.