Filtra Systems Company developed the walnut shell filter about 40 years ago. One of the attractions of walnut shell is how well it can handle oil. When oil mixes together with sand, it essentially becomes asphalt. With walnut shell, the oil is coalesced and then, when it’s backwashed, the oil can be released from the shell.
In this Water Online Radio interview, Joe Haligowski, International Sales Manager for Filtra Systems, discusses the walnut shell backwashable media filter which has to date been used primarily in industrial settings.
“What’s unique about the walnut shell is that it’s just slightly heavier than water,” states Haligowski. “Its specific gravity is about 1.2. We can lift it with our mixer. Sand is far heavier, and many other sand technologies use air, or water, or up flow to scrub the shells clean, which isn’t as efficient as being able to turn on a mixer and make a homogenous stirred slurry, when you bring the backwash water in.”
The mixer is an update to the filter which allows the shells to be cleaned once they become contaminated and fouled, and keeps the walnut shells inside the vessel throughout the cycle. The filter has also had the pressure vessel removed and replaced with a more cost-effective atmospheric tank and pump.
To learn more about walnut shell filtration, click on the audio player below: