This study presents a mathematical model of an aerobic dynamic discharge (ADD) process developed to improve the selection of efficient mixed PHA accumulation cultures. Conventional aerobic dynamic feeding (ADF) mode modeling is extended to include the ADD's physical selective pressure to favor the accumulation of PHAs accumulating bacteria. The model includes the uptake substrate, PHA degradation and synthesis and PHA inhibition. Good fit between experimental data and simulations shows that the model is able to account for the dynamic processes and thereby to simulate the selection phase and transition to the pseudo-steady state of PHA production phase. Two variables ((V-s)=(feast_end)(min) and phi-value), introduced to quantify the influence of the physical selective pressure on the PHA accumulating ability of mixed microbial cultures (MMCs), can be used for process control. (C) 2016 Elsevier B.V. All rights reserved.