Removal of Diesel Oil in Soil Microcosms and Implication for Geophysical Monitoring

Abstract

Bioremediation of soils polluted with diesel oil is one of the methods already applied on a large scale. However, several questions remain open surrounding the operative conditions and biological strategies to be adopted to optimize the removal efficiency. This study aimed to investigate the environmental factors that influence geophysical properties in soil polluted with diesel oils, in particular, during the biodegradation of this contaminant by an indigenous microbial population. With this aim, aerobic degradation was performed in soil column microcosms with a high concentration of diesel oil (75 g kg −1 of soil); the dielectric permittivity and electrical conductivity were measured. In one of the microcosms, the addition of glucose was also tested. Biostimulation was performed with a Mineral Salt Medium for Bacteria. The sensitivity of the dielectric permittivity versus temperature was analyzed. A theoretical approach was adopted to estimate the changes in the bulk dielectric permittivity of a mixture of sandy soil-water-oil-gas, according to the variations in the oil content. The sensitivity of the dielectric permittivity to the temperature effects was analyzed. The results show that (1) biostimulation can give good removal efficiency; (2) the addition of glucose as a primary carbon source does not improve the diesel oil removal; (3) a limited amount of diesel oil was removed by adsorption and volatilization effects; and (4) the diesel oil efficiency removal was in the order of 70% after 200 days, with different removal percentages for oil components; the best results were obtained for molecules with a low retention time. This study is preparatory to the adoption of geophysical methods to monitor the biological process on a larger scale. Altogether, these results will be useful to apply the process on a larger scale, where geophysical methods will be adopted for monitoring.

Kinetics and Optimization by Response Surface Methodology of Aerobic Bioremediation. Geoelectrical Parameter Monitoring

“…where R is the reaction rate, C is the residual diesel oil concentration in soil, k is the reaction rate constant, and n is the reaction order. In this study, first-(n = 1) and the second-order (n = 2) kinetics were considered due to their good fitting of experimental data, already demonstrated by previous studies [9,12,29,30].…”

“…and C/N = 120 had the highest percentage of removed diesel oil and this trend continued throughout the test; • for microcosms with C/N = 180, the highest removal was always achieved with u% = 12% b.w. 9 15 60 1 10 15 120 11 11 15 180 5 12 15 300 5…”

“…Biostimulation has proven to be one of the best solutions in terms of easiness and management of application, relative to the achieved results [2,3,7,8]. In this area, previous studies have demonstrated that good removal efficiency can be achieved when indigenous bacteria are stimulated with mineral salt media in order to aerobically biodegrade soil pollutants without any addition of other carbon sources [9,10].Given the multitude of findings, it can be useful to know the kinetics of the process for planning in situ remediation activities. Moreover, optimization of the process in terms of the optimal operative parameters for a given system of soil pollution can be of help to maximize the achievable results.Several studies [11][12][13][14][15] have shown that hydrocarbon removal can be modeled with first-or second-order reaction kinetics.…”

“…">Soil PropertiesThe soil was the same as that used for a previous study [26], taken at a depth around 3 m under the surface in Trecate (Italy), near a site polluted by a crude oil spill. Previous analyses had confirmed that the crude oil concentration was negligible [9,23]. For the tests, just the particles with size distribution between 0.15 and 2 mm were used.…”

“…Biostimulation has proven to be one of the best solutions in terms of easiness and management of application, relative to the achieved results [2,3,7,8]. In this area, previous studies have demonstrated that good removal efficiency can be achieved when indigenous bacteria are stimulated with mineral salt media in order to aerobically biodegrade soil pollutants without any addition of other carbon sources [9,10].…”