Olive mill waste water (OMW), supplemented or not with ammonium sulphate and rock phosphate (RP), was applied as a medium in a shake-flask repeated-batch fermentation with Aspergillus niger immobilized on polyurethane sponge. Compared to other treatments, the results showed higher growth of the immobilized mycelium and significant reduction of the total phenols when the waste material was enriched with RP and ammonium sulphate (N). The immobilized fungus solubilized the RP with a maximum level of soluble P of 0.58 g/litre reached during the fourth batch cycle of the OMW+RP treatment. Depending on the medium composition, three types of treated OMW were produced which could be further used for various purposes.