Disclosed is a method and a filter unit for depleting or enriching a liquid or gas with substance(s) comprising i) providing a filter unit comprising at least one convective layer and at least one receiving layer adjacent one another, ii) passing the liquid or gas through the filter so that the main direction of flow is along the layers and the main flow of liquid gas is in the convective layer, allowing the substance(s) to: a) be transferred from a convective layer to a receiving layer, and b) be retained or otherwise modified or transferred within a receiving layer, or c) be provided by the receiving layer, and d) be transferred from the receiving layer to the fluid in the convective layer.