Each experimental range of the independent variables was divided into three levels (1, 0, +1)
by ‘‘Face Centered’’ (alpha equals one) option, with 30 experiments and three controls (no inoculation). BTEX degradation percentages were assessed after incubation of 60 h. Response surface methodology was used to analyze the main and interactive effects of the four variables on BTEX degradation using the Design-Expert 7.1.5 software (Stat-Ease Inc., Minneapolis, MN, USA).