Central composite design (CCD) technique was used to develop an empirical model for the treatment of olive oil mill wastewater (OMW) by loofa-immobilized Phanerochaete chtysosporitan. The concentration of OMW (A) (i.e., 20%, 30% and 40%), concentration of ammonium sulfate as a source of nitrogen (B) (i.e., 0.25, 0.5 and 0.75 g/1) and glucose as a carbon source (C) (i.e. 3, 5 and 7 g/1), both of which used for the fungus growth, were considered as independent variables. The influence of these three regressors on the four dependent variables, i.e., chemical oxygen demand (COD), total phenols (TP), color and aromaticity removals was evaluated using second-order polynomial multiple regression model. Analysis of variance (ANOVA) showed a high coefficient of determination (R) value of 0.912-0.982, thus ensuring a satisfactory adjustment of the regression model with the experimental data. The positive sign for the coefficient of OMW concentration in the model, indicated that the COD, color and aromaticity removals increased with increased levels of this factor. While TP removal decreased with the increased concentration of OMW. The negative effect of nitrogen source concentration on the COD and color removals indicated that the response levels decreased as B increased. The positive sign for the coefficient of the interaction between two factors A and B on the removal of TP and color, indicated that a simultaneous increase in the OMW and the nitrogen source concentrations led to an increase in those responses. Although simultaneous increase in the concentrations of nitrogen source and glucose, decreased COD removal. Quadratic models were predicted for the response variables, i.e., pollutant removals, and the maximum values predicted were 64%, 88%, 48% and 39% for COD, TP, color and aromaticity, respectively. Optimum conditions for this wastewater treatment were obtained based on the performance of the loofa-immobilized P. chrysosporium in the experiment where OMW concentration was at the high level and variables B and C were each at their midrange value. (c) 2005 Elsevier Ltd. All rights reserved.