The regression coefficients and the interaction between each independent factor were also considered statistically significant for p-values below 0.05 and very significant for p-values below 0.01. As seen in Table 2, BTEX concentration (B), NaH2PO4 (D), cell mass and BTEX concentrations (AB) and cell mass and NaH2PO4 (AD) were significant model terms. The results presented the coefficient of B as very significant and the coefficients of D, AB and AD as significant.