A device for use in processing of a liquid and/or gas stream. The device is made up of a monolithic structure having active powder for treating streams. The structure has an inlet end and an outlet end and a multiplicity of cells extending from inlet end to outlet end. The cells are separated from one another by porous walls, a portion of the total number of cells being plugged in a pattern such that a stream enters the device through the unplugged cells at the inlet end and passes through at least two porous walls and the active powder in-between, and thereafter passes out of the device through unplugged cells at the outlet end. The device finds use in a number of applications including ion exchange, adsorption, biological and chemical reactions, and catalytic applications.