An in depth guide to depth filtration, What Is It And How Does It Work?

The purpose of depth filtration is to purify liquids. Filtration works entirely on the principle of particle size. If a filter has a certain pore size (expressed in micrometers, or 1/1000th of a millimeter), then this depth filter will capture the solid contaminants which are lager that the given pore size of the filter media. The particles smaller than this pore size, on the other hand, are able to penetrate through the filter media. The choice of which type of filter and the fineness of the filter depends to a large extent on the average particle size, but also on the distribution of this particle size.  
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Simply put, there are two types of filters. A surface filter, which stops particles only on the surface of the filter medium. Examples include filter bags, pleated filters and membrane filters, such as PES membrane filters or PTFE membrane filters. In addition, there are depth filters, which are able to stop particles not only on the surface, but also inside the filter medium. In particular, the thickness of the filter medium and its structure ensure that particles inside the medium are trapped.

What is the depth filter media in depth filtration like?

Depth filters are commonly made of fibres that are placed or blown in a quite random order on top of eachother, creating porous layers with depth filtration effect. We often compare it to a maze. The fibres of the filter media together create a tortuous path in which the particle retention and filter effect is made possible. Typified by multiple porous layers, a depth filter is quite effective for its' purpose of depth filtration.

When do you use what? 

Generally, depth filters are used when there is a wide variety of particle size in the liquid. For example, if we have a liquid containing particles from 10 microns to 100 microns, then a depth filter is very suitable. If we are dealing with a suspension where the size of the particles does not vary that much, for example a range from 10 microns to only 20 microns, then a surface filter may be more common. The openings in a depth filter become smaller as we go throughout the medium, rather than evenly distributed pores of the filter medium (which you will often see in membrane filters). With depth filters, the smaller particles are retained in the core and the large particles on the outer surface of the filter media. Thanks to this smart distribution, your filter has a longer lifespan and can filter more particles before becoming clogged. So the objective of depth filters and advantages of depth filtration is to filter a wide range of particle sizes much better than a surface filter does.

What types of depth filters do we have in depth filtation?

Depth filters come in many different shapes, sizes and materials. Common are cellulose depth filters, such as filter sheets and filter modules, and plastic depth filters, such as polypropylene meltblown filters, polyester meltblown filters and nylon meltblowns. 

Filter sheets and modules/lentuculars are available in different product lines. There are three standard grades. 
(1) Coarse particle filtration to fine filtration: an all-round filter, to be used in various applications. 
(2) Coarse particle filtration to sterile filtration: to remove bacteria and other micro organisms, often used in the industry of food and beverage, like fruit juices, soft drinks and more. 
(3) Sterile filtration in demanding applications: these filters are commonly used in the pharmaceutical and life science industries.

What is the difference between a filter sheet and a lenticular filter in depth filtration?

The exact filter media from which a filter sheet is made can also be built in modular form, hence the word filter modules. Filter sheets are used in a filter press, in which up to hundreds of sheets can be placed at the same time. Modules/lenticulars, on the other hand, are placed in a filtration pressure vessel, or filter housing. The advantage of the filter module is the fact that they are quickly changeable, leak-proof and bypass-free. With lenticulars, the operation of depth filters becomes much more easy. They also make backwashing in depth filters possible.

Meltblown filter cartridges

Just like the cellulose filter modules, meltblown depth filter cartridges are placed in a filter housing. There are filter housings for filter cartridges that can accommodate one filter cartridge at a time, a so-called Single Round Cartridge Filter Housing. In addition, there are cartridge filter housings that offer space for several depth filter cartridges at the same time, so-called Multi Round filter housings. By default, meltblown depth filters are nominal rated, which means that the depth filter stops particles with a nominal efficiency on the surface of the medium. Van Borselen also supplies absolute rated meltblowns depth filters, for cases where a very high efficiency of the filter is required. These filters are effective with a ratio of bèta 5000, which you would normally only find in membrane filters, such as PES membrane filters and PTFE membrane filters. At Van Borselen Filters, this efficiency is also found in our depth filter media. 

As you can see, there are no limitations of depth filtrations, since there is a suitable filtration media available for each filtration process. The main objective of depth filtration is to retain a large mass of particles in fluids which contains a high load of particles of different sizes.

Common applications in depth filtration

Depth filtration, typified by multiple layers of porous filter media, is used in many different applications. For exmaple, it's commonly used in either drinking water treatment systems and waste stream systems. But, it's also used during manufacturing paints, organic solvents, ink and other chemicals. We can also find them in the production of food and beverage, fruit juices, soft soda's and other drinks. And last but not least, we will find them during the production of valuable liquids too in the pharmaceutical industry or life science. As you can see, there a no limitations to depth filtration.

Need advice? 

Call 0031 (0)79 34 12314 or email Request@vanborselen.nl for a competitive offer or tailor-made advice. You can also use our chat. We are happy to help you improve your depth filtration and separation process. Make an appointment today for a face-to-face meeting, where we'll discuss your needs and offer tailored advice that really makes a difference to your business. At Van Borselen Filters, we go further than just supplying products; We offer an experience based on trust, expertise and a true commitment to your success.