Fish Lead to Filter Breakthrough

Paddlefish a filter feeder

A clog-resistant filtration system inspired by filter-feeding fish

The trouble with traditional filters is that they can’t do their job without clogging.

William & Mary ichthyologist Laurie Sanderson has a patent pending on a new type of filter that is designed to be clogless, or at least clog-resistant. The design is based on the fluid dynamics of filter-feeding fish. She is the author, along with several William & Mary undergraduates, of a paper presenting the novel fish filtration mechanisms in Nature Communications.

Shad a filter feeder

 She used an ear, nose and throat endoscope, less than a millimeter in diameter. “What we saw right away was that fish mouths weren’t filtering the way we thought they were,” Sanderson said. The understanding at the time, which persists in many texts today, was that the black box structure acted as a dead-end sieve like a spaghetti strainer or a coffee filter.

“That’s not what we saw with the endoscope,” she said. “We saw fluid and particles moving parallel to the filter. By the early 2000s, we had combined the endoscopy with computational fluid dynamics and realized that a diversity of fish species were using crossflow filtration. However, this just created another puzzle, because the fish crossflow filter never clogs, even though industrial crossflow filters always clog."

Whale Shark a filter feeder

 “The fish use these backward-facing steps and the resulting recirculation regions to manipulate and concentrate the particles,” she explained. The vortices also act as a “hydrodynamic tongue,” keeping the concentrated particles moving through the system — without clogging.

“This is something that potentially can be of use to industry,” Sanderson said. “Other filters use various kinds of knobs, baffles, ridges and corrugations. Engineers have been very clever in designing crossflow and other types of filters.”

Jason McDevitt, William & Mary’s director of technology transfer, notes that Sanderson’s design is different enough for it to get patent pending. Sanderson says that one advantage of her concept is that it could be used to design filters that would separate out particles in a controlled fashion, directing the particles in any desired direction.

Filtration is a very big process in a wide variety of industries. A breakthrough in a non-clogging filter would be a big deal, and potentially a huge money maker. But it sounds pretty tough. Fish mouths are moving and adaptive, but filters tend to be fixed. Making them adaptive would raise the level of complication quite substantially.

Wombat-socho has "Rule 5 Sunday: Time Begins on Opening Day" ready for sampling at The Other McCain.