Rotating a helical membrane for turbulence enhancement and fouling reduction

To reduce fouling, enhance turbulence and permeate flux in membrane filtrations, similar to the rotating disk membrane modules, in this paper, a new helical membrane was rotated and its features in filtrating different particle suspensions such as yeast, kaolin and CaCO3 in a cylindrical container were studied. About 27% enhancement of stable flux can be maintained by rotating a 360° helical membrane, comparing with rotating a same sized flat membrane, at a rotating speed of 160 rpm. The flux enhancement and fouling reduction were affected by the helical angles (best at 360°) of the membrane module, the enhancement in turbulence intensity and the hydraulic flow regime and dimensions, such as the ratio of the membrane width to the diameter of the separation unit. The stable permeate flux of rotating a 360° helical membrane were higher than that of rotating a flat membrane both at 5.3 kPa or 6.5 kPa, a higher flux enhancement at 6.5 kPa was observed. The order of membrane fouling was yeast > kaolin > nano-CaCO3 when the particles concentrations were all at 5.0 g l−1. Fouling is less severe when the diameter of separation units is smaller, and vice versa. Rotating a helical membrane is specifically useful for stirring separations without aeration.

► Rotating a helical membrane can maintain higher flux than rotating a same sized flat membrane, with better mixing effect.
► It created higher axial (vertical) Reynolds numbers and Taylor numbers than rotating a flat one.
► It enhanced turbulence on the membrane surface.
► It generated better vortex mixing or secondary flows, clearly shown by a visualized particle tracer test.