Optimization of phenol biodegradation by immobilized Bacillus subtilis isolated from hydrocarbons-contaminated water using the factorial design methodology

The ability of newly isolated bacteria, identified as Bacillus subtilis immobilized on alginate hydrogel beads, to degrade phenol was investigated under different parameters, such as phenol concentration, bead diameter and inoculums size, and was optimized using full factorial design methodology. A mathematical model that governs the degradation of phenol by the immobilized system was obtained and it fitted the experimental data very well. The model indicated that within the range of variables employed, all the parameters and their interactions influenced the biodegradation process, whereby the phenol concentration was the most significant factor. B. subtilis revealed a very high degradation activity and could be grown using phenol as the sole source of carbon. Phenol was degraded by the new bacteria in 8 h under the optimum conditions obtained by the desirability function: 100 mg L-1 phenol concentration, 3 mm beads diameter and 244.5 mg of cell dry per liter biomass size, with a desirability value of 91.25 %.