Statistical optimisation for improvement of phenol degradation by Rhodococcus sp. NAM 81

Abstract

Phenol is an important compound widely used in formulation of dyes, pesticides, in fabrication of plastics, as well as being generated in several industrial effluent other industries. In the present study, ability of phenol-degrading bacteria sp. NAM 81 was characterised by optimising the important parameters that were able to support phenol degradation abilities using two-step statistical. Fractional factorial design (FFD) was applied to select significant variables (temperature, pH, phenol concentration, ammonium sulphate concentration, sodium chloride concentration, incubation time) that affects percentage of phenol degradation. pH (B), phenol concentration (C), sodium chloride (E) and incubation time (F) were observed to be significant (P≤0.05), which was further optimised for phenol degradation and cell growth, using response surface methodology (RSM) based on central composite design (CCD). From the optimisation by CCD, pH 7.25, 0.74 g l-1 of phenol with 0.06 g l-1 of NaCl concentration in 23 hrs of incubation time is the best condition for phenol degradation. Meanwhile, sp. Rhodococcus NAM 81 grow best in pH 7.72, 0.85 g l-1 of phenol, 0.06 g l-1 of NaCl for 24 hrs incubation time were the best condition predicted to produce 0.867 g l-1 of sp. NAM 81 cells. Verification of experiment indicated no significant different between the predicted and experimental data (P≥0.05) for phenol degraded performance, as well as Rhodococcus growth. Under optimum conditions, the proposed method was successfully applied to improve 1.2 fold of phenol degradation and 1.3 for cell growth as compared to non-optimal cultivation.