FLUID TREATMENT ELEMENTS AND FLUID TREATMENT ARRANGEMENTS WITH FLUID TREATMENT ELEMENTS HAVING UNEVEN SURFACES

Fluid treatment arrangements and elements and methods for making and using fluid treatment arrangements and elements are disclosed. A ribbon including a permeable fluid treatment medium may be spirally wound in a plurality of windings to form a fluid treatment element having a disk-shaped body. The disk-shaped body may have first and second opposite end surfaces, e.g., an inflow surface and an outflow surface, and an outer rim. One or both of the end surfaces may be an uneven surface. At least two and as many as many as fifty or more fluid treatment elements may be positioned along a hollow core assembly. Fluid may be directed to or from the interior of the core assembly through each fluid treatment element. In each fluid treatment element, fluid flows from the inflow surface to the outflow surface generally edgewise through the permeable fluid treatment medium.