Emission of VOC and GHG by Bioremediation of Soil Contaminated with Diesel

Abstract

Bioremediation processes have been credited for reducing high levels of organic contaminants from soils. However, during bioremediation of diesel contaminated soils, for instance, diesel is converted to volatile organic compounds (VOC) and greenhouse gases (GHG), which means that such remediation technique contributes to the greenhouse effect. The ongoing construction of a large petrochemical industrial region in Rio de Janeiro Metropolitan Area (COMPERJ) and the transportation of large volumes of oil byproducts (mainly diesel), have raised deep concerns regarding accidents that may result in soil and air contamination. When the problem comes, remediation techniques shall be applied. The objective of this study was to characterize the emission of GHG and VOC during bioremediation of soils contaminated with diesel oil in pilot scale. Soil samples contaminated with 0.5, 2.0 and 4.0 w/w% diesel oil were kept during 3 months in glass rectors (2 L internal volume) kept under anaerobic/anoxic conditions. The soil moisture was controlled at 80% of field capacity. Bioremediation processes were investigated with nutrient’s adjustment (biostimulation), no adjustment (natural attenuation) and sterilized soil (abiotic process). The gases emitted from different reactors were collected in activated carbon cartridges and the GHG were collected in Tedlar bags. The chemical analyzes were performed using a gas chromatograph (Agilent 7690) with multi-detection using FID for CH₄, ECD for N₂O and TCD for CO₂. VOC were analyzed using a mass spectrometry detector (Varian 450GC MS220). The results indicated that gaseous samples contained high concentrations of CO₂ but low concentrations of CH₄ and N₂O. The differences in composition of the gas emitted from the reactors regarding CO₂ were statistically not significant. Preliminarily, regarding VOC emissions, such as alkanes and alkenes (both branched), cycloalkanes, and aromatic substituted (such as ethyl benzene), the compounds with higher emissions were cycloalkanes and branched alkanes.