A filter module (12) is proposed which includes a multiplicity of tubes arranged in side-by-side disposition to provide an annular array of flow passages (16) disposed about a common centre (17). The tubes comprise a filter material, and the disposition thereof is such as to maximize the filtration area whilst minimizing space utilization. A plurality of filter modules (12) is arranged in stacked relationship, corresponding tubes of the respective elements being in fluid flow relationship and one end of the stack being closed by a bottom plate (33). (FIGS. 1 and 2).