  Despite intensive research, fouling remains a severe problem in membrane
filtration. It is often controlled by applying turbulent flow which requires a
higher energy consumption. So-called turbulence promoters or static mixers can
be inserted into the flow channel of tubular membranes. They deflect the fluid,
induce vortices, enhance particle back-transport and increase the shear rate at
the membrane surface, thus mitigating fouling. However, little is known how the
geometry of such turbulence promotors affects the reduction of fouling. We
investigate how different 3D-printed mixer geometries affect fouling and
improve the flux during filtration with humic acid. Most mixer geometries used
in the present study are based on a twisted tape; a Kenics static mixer is
investigated as well. Static mixers with changing diameter prove to be less
effective than twisted tape mixers with constant diameter which lead to an
increase in permeate flux of around 130%. The highest flux improvement of 140%
can be reached by applying a Kenics mixer. Regardless of their geometry, all
investigated static mixer cause higher permeate fluxes at same specific energy
consumption. Again, the Kenics mixer proves to be the most efficient static
mixer. The presented mixer geometries can be fabricated with undercut injection
molding techniques and represent a simple and viable option to make tubular
membrane based filtration processes more efficient.
