Kinetics and optimization by response surface methodology of aerobic bioremediation. Geoelectrical parameter monitoring

This study aimed to investigate the kinetics of an aerobic bioremediation process of diesel oil removal by indigenous microorganisms, and to define the optimal operative conditions by means of response surface methodology. This was carried out by setting up a series of microcosms (200 g of soil), polluted with the same diesel oil concentration (70 g·kg−1 of soil), but with different water contents (u%) and carbon to nitrogen (C/N) ratios. The process was monitored by: (1) residual diesel oil concentration, to measure the removal efficiency, and (2) fluorescein production, to check the microbial activity. These two parameters were the objective variables used for the analysis of variance (ANOVA) and response surface methodology (RSM). The results allowed the interactions between u% and C/N to be defined and the optimal range to be adopted for each. The process kinetics was modeled with first- and second-order reaction rates; slightly better results were achieved for the second-order model in terms of parameter variability. Biological processes like degradation may have effects on dielectric properties of soil; an open-ended coaxial cable was used to measure the dielectric permittivity of microcosm matrices at the start and after 130 days of bioremediation. The evolution of the real and the imaginary components of dielectric permittivity provided results that supported the evidence of a biodegradation process in progress.