Process for treating and/or removal of substances from liquid, especially whole blood

A process for treating a liquid to remove a substance therefrom comprising the steps of providing a chamber including a microporous semi-permeable membrane filter, a first liquid containing said substance to be removed in direct contact with one side of said membrane filter, and a second fluid in direct contact with the other side of said membrane filter, wherein at least a portion of said first liquid containing said substance is capable of penetrating said membrane filter, wherein a substance removal agent is immobilized with regard to said membrane such that the substance removal agent contacts said penetrating portion of said first liquid but does not directly contact said first liquid itself, and wherein said substance removal agent is selected from the group consisting of material capable of adsorbing said substance, material capable of reacting biologically with said substance to remove said substance, and mixtures of such materials;

• withdrawing a portion of said second fluid from said chamber to create a first predetermined pressure for said second fluid below that of the first liquid;
• and supplying said second fluid to said chamber to create a second predetermined pressure for said second fluid above that of the first liquid;
• wherein said withdrawing and supplying steps cause said penetrating portion of said first liquid to flow in an alternating path in the pores of said membrane filter to effect contacting of said penetrating portion containing said substance with said substance removal agent.