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

Carla Maria Raffa,Francesca Bosco,Fulvia Chiampo,Alberto Godio,Andrea Vergnano,Barbara Ruffino

doi:10.3390/app10010405

Carla Maria Raffa, Francesca Bosco + Show 4 more

Open Access

https://doi.org/10.3390/app10010405

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Journal: Applied Sciences	Publication Date: Jan 5, 2020
Citations: 12	License type: CC BY 4.0

Affiliation: Polytechnic University of Turin

Abstract

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.

Highlights

Aerobic bioremediation of polluted soils is becoming a common technique to clean up areas contaminated with a variety of biodegradable compounds
The findings showed that a limited amount of pollutant was removed, in both carbon to nitrogen ratio (C/N) ratios, independently of the water content
The experimental tests on microcosms polluted with diesel oil at a constant concentration (70 g·kg−1 of soil) but with different water contents (u%) and carbon to nitrogen ratios (C/N) were designed according to the factorial analysis, to get experimental results useful to model the process kinetics; to study the interactions between these two operative factors, u% and C/N; to optimize the operative conditions to remove pollution in a reasonable time and with good efficiency with limited number of tests but exploiting their links to highlight their interactions, if any

Summary

Introduction

Aerobic bioremediation of polluted soils is becoming a common technique to clean up areas contaminated with a variety of biodegradable compounds. Its success is due to some features that must be considered when a soil remediation technique must be chosen: it is cheap, easy to manage, and environmentally compatible, even if it is slow and time consuming. It can be considered a “green” technique and a valid alternative to chemical methods. Together with heavy metals and metalloids, biodegradable compounds represent the main group of pollutants in soil, even if at low levels. Their origin is usually anthropogenic, due to industrial activities or events linked to them. Due to its wide use, diesel oil is an example

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