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Blog Advantages Of Walnut Shell Media

Advantages Of Walnut Shell Media

Walnut Shell Media Filter has a variety of advantages over other options in industrial filtration, especially when filtering oil and total suspended solids (TSS).

Because our system is a backwashing filter, Walnut Shell Filters not only are much better filters but are more efficient in many processes because:

  • Hydrocyclones are often used for removing oil from water, but will not fully polish the water. For example, oil droplets smaller than 20 microns are typically not removed by hydro cyclones.
  • Cartridges and bags are also frequently used but must be disposed of. Maintenance personnel is also required to change the filter media when it becomes plugged. Increasing restrictions on disposal in certain industries have also led to skyrocketing disposal costs.
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How Backwashing Filters Work For You

When compared to hydrocyclones and disposable media filters, backwashing deep bed filters have these distinct advantages:

  • Contaminants are captured by a granular media bed and then removed by an efficient tortuous path through the media bed.
  • After the bed becomes full of contaminants, it is then backwashed, which cleans the bed without incurring media disposal costs.
  • For the filter to operate at high efficiency over a long period of time, all contaminants from the bed must be removed during the backwash.

Better Filtration

One huge advantage of walnut shell media is its superior filtration of wastewater.

For example, Walnut Shell Filters will typically remove 95% of solids at 5 micron, and 90% of suspended oil.

Unlike in sand filters, whose captured oil films over the surface, captured oil remains as droplets. These absorbed droplets will then contact smaller droplets, which coalesce onto the larger droplets and increase the removal rate of small particles over time.

That's why black walnut shells have an oil absorption capacity that is 2-3 times that of sand.

Improved Efficiency

One of Filtra-Systems' goals is to provide industrial filtration solutions that can improve your company's operations in multiple ways.

Filtration systems that require less maintenance not only help reduce upkeep costs, they also help to ensure that needless interruptions of operations which can have a negative impact on your company's bottom line do not occur.

Even better, Walnut Shell Filters media beds don't require replacement for the entirety of the product's life. Because walnut shells are preferentially wetted by water, oil is easily rinsed from the shells during a backwash.

Black walnut shells (as opposed to English walnut shells) have a high modulus of elasticity, which explains why the beds won't need to be replaced. The expected yearly attrition rate is only about 2%, which is much lower than English walnut shells, pecan shells, and other types of media.

And better yet, these filtering systems need less floor space to operate, freeing up room for other machinery.

By the way, walnut shell filters are typically sized at 10-12 gpm/ft2, which is a greater flux than competing media filters. The higher flux means smaller filter housings can be used, which translates to more floor space.

The fact is, less water required to regenerate the bed is another benefit you'll enjoy. The flux required for fluidization of the bed is only 4.5 gpm/ft2 (based on a clean media bed, oil and solid saturation will increase this requirement), which is significantly lower than competing technologies.

Known Frustrations Of Sand Filters

To those who have had the misfortune of operating a sand filter, no explanation is needed for the common term "mudball."

To the uninitiated, mudballs form when sand filters are exposed to oil which results in an oil film across the sand. This film prematurely clogs the filter, drastically reducing the system's efficiency. The plugged bed has a decreased filtration area, and will backwash more frequently.

Unfortunately, even after backwashing, the bed remains unclean because the backwash water does not penetrate the film and channels around the mudballs. As the problem persists the bed will inevitably need to be replaced, a manual operation that requires your personnel to hand dig out the clogged bed.

This adds to unnecessary costs, both in paying trained personnel and expensive system downtime. Is pricey filter replacement and disposal costing you time and money?

Generally, sand filter beds need to be replaced every five years. However, with regular exposure to oil, replacement time can be reduced to as frequently as every six months.

An alternative to filter replacement is to clean the filter bed, a procedure that involves soaking the bed with a condensate, or light oil. The time-consuming nature of this process means that sand filter users typically choose to replace the bed instead.

Sand is also an OSHA dusting hazard and handling sand to replace the bed can result in exposure to plant personnel. Sand filters typically use an air scour to remove oil and solids from the media bed.

Drawbacks to sand filter technology include:

  • Incomplete fluidization of the media bed
  • Extra piping and valves required upon installation
  • A larger compressor and air regulator are needed
  • Possible installation of a vapor recovery and processing unit (VRU)

The compressed gas needed for this operation may also change the electrical classification of the area to Class 1, Div 1, increasing electrical costs for all process equipment nearby.

The backwash volume required for sand filters can be up to 5 times more than for walnut shell filters.

Sand filters are designed at 6 gpm/ft2, and the flux required for fluidization of the bed is 12 gpm/ft2 (based on a clean media bed, oil and solid saturation will increase this requirement).

Known Concerns Of Anthracite

Another common media filter is anthracite.

Anthracite filters usually have three layers of differently sized media: a top layer collects coarse contaminants, the second layer collects smaller particulate, and the third layer is the final polish.

Unfortunately, substantially more water is needed to clean anthracite filters. Why? Because the backwashing process requires a subsurface wash to break up any waste before the standard backwash.

In fact, an anthracite filter may require seven times more water to backwash than a comparable walnut shell filter!

Additionally, upset conditions can cause the media to mudball. The attrition rate for anthracite is much higher than walnut shells, and the media generally needs to be replaced every year. Anthracite filters are designed with a flux of 4-4.5 gpm/ft2.


Filtration Design Flux

Backwash Fluidization Flux

Backwash Volume (compared to WSF)

  Walnut Shell Filter

12 gpm/sqft

4.5 gpm/sqft


  Sand Filter

6 gpm/sqft

12 gpm/sqft


  Anthracite Filter

4 gpm/sqft




We invite you to call now, 248-427-9090. Talk to one of our expert filtration engineers and get help selecting the perfect filters.