Integrated use of chemical and geophysical monitoring to study the diesel oil biodegradation in microcosms with different operative conditions

Carla Maria Raffa,Fulvia Chiampo,Alberto Godio,Andrea Vergnano

doi:10.1007/s40201-021-00681-2

Carla Maria Raffa, Fulvia Chiampo + Show 2 more

Open Access

https://doi.org/10.1007/s40201-021-00681-2

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Abstract

This study aimed to monitor the aerobic bioremediation of diesel oil-contaminated soil by measuring: a) the CO2 production; 2) the fluorescein production; 3) the residual diesel oil concentration. Moreover, the complex dielectric permittivity was monitored through an open-ended coaxial cable. Several microcosms were prepared, changing the water content (u% = 8–15% by weight), the carbon to nitrogen ratio (C/N = 20–450), and the soil amount (200 and 800 g of dry soil). The cumulative CO2 and fluorescein production showed similar trends, but different values since these two parameters reflect different features of the biological process occurring within each microcosm. The diesel oil removal efficiency depended on the microcosm characteristics. After 84 days, in the microcosms with 200 g of dry soil, the highest removal efficiency was achieved with a water content of 8% by weight and C/N = 120, while in the microcosms with 800 g of dry soil the best result was achieved with the water content equal to 12% by weight and C/N = 100. In the tested soil, the bioremediation process is efficient if the water content is in the range 8–12% by weight, and C/N is in the range 100–180; under these operative conditions, the diesel oil removal efficiency was about 65–70% after 84 days. The dielectric permittivity was monitored in microcosms with 200 g of dry soil. The open-ended coaxial cable detected significant variations of both the real and the imaginary component of the dielectric permittivity during the bioremediation process, due to the physical and chemical changes that occurred within the microcosms.

Highlights

The soil contamination by hydrocarbons is a current problem due to anthropic activities, that should be solved in an Different biological remediation approaches were studied and compared to evaluate the most efficient one for the degradation of a specific contaminant [3,4,5]
Since each soil has its biological diversity and requirements, the optimal water content (u%) and the carbon to nitrogen ratio (C/N) are crucial in biostimulation process: 1) the water content allows the dispersion of soil aggregates and the contaminant diffusion in the aqueous phase, and promotes the contact between microorganisms and pollutants [12]; 2) the carbon to nitrogen ratio is useful to define the correct amount of nutrients since their excessive or scarce amount can inhibit the biological activity [13, 14]
Each microcosm consisted of a sealed glass jar filled with different amounts of soil, spiked with the same amount of diesel oil (70 g/kg of dry soil), and kept in different conditions of water content and C/N ratio

Summary

Introduction

The soil contamination by hydrocarbons is a current problem due to anthropic activities, that should be solved in an Different biological remediation approaches were studied and compared (i.e. natural attenuation, bioaugmentation, biostimulation) to evaluate the most efficient one for the degradation of a specific contaminant [3,4,5]. The growth of indigenous microorganisms is enhanced by optimizing physical and chemical process conditions to get efficient pollution. Since each soil has its biological diversity and requirements, the optimal water content (u%) and the carbon to nitrogen ratio (C/N) are crucial in biostimulation process: 1) the water content allows the dispersion of soil aggregates and the contaminant diffusion in the aqueous phase, and promotes the contact between microorganisms and pollutants [12]; 2) the carbon to nitrogen ratio is useful to define the correct amount of nutrients since their excessive or scarce amount can inhibit the biological activity [13, 14]

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