However, at the moment, the interest is moving to the application of microbial mixed cultures (MMCs), using waste streams as substrate characterized by their large organic matter content. In this latter case, PHA can be produced by MMCs selected by the exploitation of the ecological role of PHA as a microbial storage material [3], when dynamic operational conditions are applied to the system. A selective pressure is imposed, favouring the selection and growth of different microbial cultures able to have clusters of internal carbon as reservoirs