A mathematical model that describes strain growth, product formation and medium consumption is used to predict the performance of batch fermentation of Zoogloea sp. GY3, screened from activated sludge. Zoogloea sp. GY3 is useful in synthesizing polyhydroxyalkanoates (PHAs). The model is based on the Logistic equation for microorganism growth, the Luedeking-Piret equation for production of PHAs and a Luedeking-Piret-like equation for sucrose consumption, and appears to provide a reasonable description of the behavior of each parameter during the growth phase. The results show that the production of PHAs is growth-associated, and the model predictions are in satisfactory agreement with measured data. (c) 2006 Society of Chemical Industry.