This paper addresses certain aspects of the design and development process aiming at reducing the radioactivity of liquid low-level waste streams (LLLW) to a very low level. Two types of membrane processes are being examined : ultrafiltration (UF) and seeded ultrafiltration (SUF). The UF membrane enables the removal of very fine particles of solid material From liquid radioactive waste. Only the particles with molecular weight above the cut-off of the UF membrane are retained. Much greater radioactivity removal may be achieved if the effluent is treated with high-molecular-weight ligands that form complexes with radioactive ions or small-sized radioactive molecules. This paper presents results of experiments consisting of decontamination of model radioactive effluents, simulated waste, and original LLLW by using several ligands for binding the radioactive ions of Cr, Co and Cs.