The invention relates to a process for the treatment of an organic and/or inorganic substrate, where the support used for an active component, for example a biocatalyst, such as a microorganism or an enzyme, is granules made of a solid foam into the continuous phase of which magnetizable particles are incorporated, so that the support with the biologically active component immobilized thereon can be separated from a mixture by means of a magnetic separating device. The invention furthermore relates to a magnetizable aggregate and to a process for its preparation.