Understanding the fluid that you are going to filter is important when deciding to use either depth filtration or surface filtration. The main difference is that, with surface filtration, the particles are retained mostly on the surface of the media, and for depth filtration, the particles are either in a thicker media or multiple layers of media form a torturous path.
What is Depth Filtration?
To understand how depth filtration works, it is helpful to imagine a path with many layers. Mediums of water move through the different stratums at various speeds and sizes based on what they are composed of. For example, particles that are larger will be found in closer proximity to the surface because their size permits them greater mobility than finer elements which can only enter laterally or from below due to their smaller size. The medium layer is thick, so fine particles cannot pass by thicker ones as easily and instead remain trapped within its "walls" where irregular pores provide additional obstacles for even those who may otherwise manage an escape.
Depth filtration is commonly applied in polishing filtration applications including, but not limited to:
•Essential oil and extract clarification •Haze removal in distilled spirits •Blood fractionation operations recovering plasma•Transformer oil filtration and water removal•Bulk Chemical Production•Large volume Parenteral Solutions
What is Surface Filtration?
Surface filtration is a process, often used in water filtration systems, to remove particles from the surface. The particles retained form a layer of material, commonly called “cake layer.” The cake layer helps increase efficiency of this process and is formed when retained particles form a thin sheet over time.
Surface filters are typically used before chemical or biological treatments, such as chlorine disinfection. Surface filtration comes first because the filters’ surfaces cannot withstand harsh chemicals. They still have an important role in that they remove any large pieces that may have otherwise clogged the final filter stages.
What’s the Difference Between Depth Filtration and Surface Filtration?
In surface filtration, particles are mostly held on the surfaces of media and retained in a layer. This increases efficiency because there is more filtering material to catch debris. In depth filtration, multiple layers or thicker materials provide an intricate path for other things that shouldn't be released into a water source, such as dirt and chemicals, from passing through it. The main difference is that depth filtration forms a torturous path to retain particles and surface filtration particles are mostly held on the surface.
It is interesting to note that we have not found a universal or industry standard for "nominally" rated filter media. Each manufacturer selects its materials based on their specifications and definitions of what constitutes the term, so if you're comparing prices, one bag might be more expensive than another depending on the different brands' methods.
Which is Right for You?
Depth filtration is a bit more expensive than surface-level, but it lasts much longer. The choice of filter mechanism depends on the usage you plan for it – if your source has lots of debris and needs heavy-duty filtering then depth will be necessary. Otherwise, start with something that’s a little less expensive, such as manually cleaning or sand filters. Later on, you may decide depth filtration is right for your application.
