US researchers design water filtration system based on manta rays

RESEARCHERS in the US have developed a new water filtration design based on the feeding system in types of stingray.

The new design, published in the Proceedings of the National Academy of Sciences, uses a 3D-printed model of the plates that mobula rays use to feed on plankton. Mobula rays – the family of stingrays which includes manta rays and devil rays – inhale water as they swim, filtering out plankton to feed on. The excess water is then ejected out through its gills. Engineers at Massachusetts Institute of Technology were able to translate this system to filtering pollutants out of water.

In industrial water filtration systems, the critical trade-off is between the amount of water that can filter through versus how well it blocks specific pollutants. The MIT team found that manta rays strike a highly effective balance which allows enough water through to absorb oxygen while blocking sufficient plankton to feed on.

How do manta ray-based water filters work?

The MIT engineers built a pipe from two flat panels glued together at the edges. At one end of the pipe, they inserted a 3D-printed structure of grooved plates resembling those found in the mouth of a manta ray.

When they pumped water through the plates, they found that vortices formed between the plates as the water speed increased. While water still flowed through the plate filter into the pipe, any particles trapped in the vortices were blocked, similar to a knot of hair between the teeth of a comb. These particles travelled across the face of the filter, effectively forming a crossflow filtration system, a popular mechanism for industrial water filtration. 

The team wants to see the design used  for industrial water decontamination, including at sewage treatment plants. Anette Hosoi, one of the study’s authors, said: “We have provided practical guidance on how to actually filter as the mobula ray does…the mobula ray is giving us a really nice rule of thumb for rational design.”