Optimization of Diesel Biodegrading Conditions Using Response Surface Methodology Based on Central Composite Design

Abstract

During biodegradation of petroleum products which are the main sources of aromatic compounds, optimization is the major strategy that enhances the performance of the participating organisms. This research aimed at optimizing diesel degrading conditions using the response surface methodology (RSM) based on full factorial central composite design (CCD). Bacteria were isolated from the diesel contaminated soil which were screened based on diesel oil tolerance. Bacteria resting cells (1.5 × 105 cells/ml) of the screened strains were used to formulate consortia using mathematical permutation approach on Bushnell Haas Agar before being tested on heavy metals co-contaminants. Optimization based on CCD was carried out to pH, temperature, salinity, and substrate concentration. The results indicate a total of 47 bacteria were isolated where 4 were finally screened based on their survival at the sole expense of 4% v/v diesel with high growth populations. These bacteria were identified as Alcaligenes sp., Ochrobactrum sp., Alcaligenes aquatilis, and Alcaligenes faecalis UMYU001 (MN519483.1) which were used for the formulation and selection of effective degrading consortium. The selected consortium performed better even in the presence of more than 1 g/L of different heavy metals co-contaminants producing population higher than 1.6 × 104cfu/mL (p-value = 0.0037). Based on the CCD results, parameter values of 7.14 pH, 32 °C temperature, 2.58 g/L NaCl, 3.74% v/v diesel substrate were found to be the optimum conditions for the diesel biodegradation. The interactions among these parameters generated 8.4 × 106cfu/ml which were validated by correlating the predicted and actual experimental results.