Development of helical, fish-inspired cross-step filter for collecting harmful algae

Abstract

A new filter was developed to collect harmful algae colonies by adapting the cross-step filtration structures and mechanisms discovered recently in filter-feeding fish. Extending beyond previously published models that closely emulated the basic morphology of the fish, the new cross-step filter's major innovations are helical slots, radial symmetry, and rotation as an active anti-clogging mechanism. These innovations enable the transport of concentrated particles to the downstream end of the filter. This advance was made possible by recognizing that biologically imposed constraints such as bilateral symmetry do not apply to human-made filters. The use of helical slots was developed in a series of iterative tests that used watertracing dye and algae-sized microspheres. The major products of the iterative tests were refinements in the helical design and an understanding of how varying the major structural parameters qualitatively influenced fluid flow and filter performance. Following the iterative tests, the clogging behavior of select filters was quantified at high particle concentrations. Vortices in the helical filter were effective at reducing clogging in the center of the slots. By considering the design space that is free of the biological constraints on the system and exploring the effects of variations in major structural parameters, our work has identified promising new directions for cross-step filtration and provided key insights into the biological system.

Suspension feeders: diversity, principles of particle separation and biomimetic potential

“…These organisms use varying material properties and/or fluid flows within their cross-flow filtration to influence the interaction of particles and the separation medium. In the ricochet mechanism of manta rays, the particles bounce off the filtering lobes towards the oesophagus [ 23 ], in pump-feeding fishes, the gill arches induce the formation of vortices known as cross-step filtration [ 24 ] and in bowhead whales, the flow is diverted by the tongue and pressed along the baleen fringes that change in porosity depending on flow speed [ 175 ]. In all of these mechanisms, particles smaller than the mesh size are retained and the tangential flow reduces the clogging rate.…”

“…Besides their ecological role, the separation mechanisms by which SFs separate food particles have also been of interest for engineers. The SFMs of manta rays inspired a nanofibrous membrane for oil–water separation [ 22 ] and led to the identification of a novel non-clogging filtration mechanism, called ricochet filtration [ 23 ], whereas suspension-feeding fish have inspired a helical, cross-step filter for collecting harmful algae [ 24 ].…”

Hydrodynamic analysis of bioinspired vortical cross-step filtration by computational modelling

“…branchial arches, gill rakers and denticles) that generate vortices owing to flow separation, just as bridge pilings and tree trunks generate eddies that swirl downstream [ 8 , 9 ]. Research on three-dimensional-printed models of fish filtering structures has shown that these vortices can suspend, concentrate and transport particles during vortical cross-step filtration [ 12 , 13 ]. In paddlefish ( Polyodon spathula ) and basking sharks ( Cetorhinus maximus ), the steps are formed by the sequentially arranged branchial arches that are directly exposed to the mainstream flow when these species ram suspension-feed by swimming forwards with an open mouth ( figure 1 a,b ).…”

Biomimetic crossflow filtration with wave minimal surface geometry for particulate biochar water treatment

“…Researchers have used biomimetic designs in several applications ranging from ion-mediated membranes [37,38], oil-water emulsions filtration [39], and crossflow filtration [13,19,40]. Sanderson et al [13] found that the vortices formed between the gills during crossflow enabled the fishes to capture particles without clogging.…”

“…Sanderson et al [13] found that the vortices formed between the gills during crossflow enabled the fishes to capture particles without clogging. The continued efforts helped develop a new filter design such as a helical-shaped filter that transported the particles at the downstream end of the filter [40]. Similarly, Liao et al [39] prepared a filter mesh inspired by armors and scales of shellfish, which effectively prevented them from marine oil contamination.…”