Sequential Application of Soil Vapor Extraction and Bioremediation Processes for the Remediation of Ethylbenzene-Contaminated Soils

Abstract

Soil vapor extraction (SVE) is an efficient, wellknown and widely applied soil remediation technology. However, under certain conditions it cannot achieve the defined cleanup goals, requiring further treatment, for example, through bioremediation (BR). The sequential application of these technologies is presented as a valid option but is not yet entirely studied. This work presents the study of the remediation using sequential SVE and BR. The obtained results allow the conclusion that: (1) SVE was sufficient to reach the cleanup goals in 63% of the experiments (all the soils with NOMC below 4%), (2) higher NOMCs led to longer SVE remediation times, (3) BR showed to be a possible and cost-effective option when EB concentrations were lower than 335 mg kgso −1 , and (4) concentrations of EB above 438 mg kgso −1 showed to of ethylbenzene (EB)-contaminated soils, with different soil water and natural organic matter (NOMC) contents, be inhibitory for microbial activity.

Biocomplementation of SVE to achieve clean-up goals in soils contaminated with toluene and xylene

“…According to the results presented in previous works, the native microorganisms of the soils used in this work showed to be the ones with the best degradation rates; this fact supported the use of these microorganisms in the BR experiments (Soares et al 2010(Soares et al , 2012. These experiments were performed in those cases (soils P2,14 and P4,24), where after the application of SVE, the soils presented contamination levels above the legal limits.…”

“…Both samples were obtained from the region around Porto, Portugal; after the collection, they were stored in appropriate vessels. These soils were the same as the ones used in previous works (Soares et al 2010(Soares et al , 2012.…”

“…Furthermore, the concentration of the contaminants and their properties (structure, solubility, toxicity, among others) will control the availability and biodegradability of the contaminants, influencing the remediation. Experiments performed in different soils contaminated with ethylbenzene showed that microbial activity was inhibited when ethylbenzene concentrations were higher than 438 mg/kgsoil, restraining the remediation and impeding the achievement of the clean-up goals (Soares et al 2012). Contaminants with low water solubility have limited availability to microorganisms, which represents a potential problem for bioremediation processes (Cameotra and Makkar 2010).…”

“…However, it is not clear in what situations SVE is sufficient, when it requires complementary BR, and at what point BR should be applied. In previous works performed in distinct soils contaminated separately with benzene and ethylbenzene, SVE and BR were successfully combined, achieving the clean-up goals in 100 % of the cases for soils contaminated with benzene and 89 % for soils contaminated with ethylbenzene (Soares et al 2010(Soares et al , 2012. A wider view and knowledge of this subject is achieved by experimenting and studying other contaminants.…”

Soil vapor extraction of wet gasoline-contaminated soil made possible by electroosmotic dewatering–lab simulations applied at a field site

“…Diesel fuel is biologically readily degraded when bottlenecks for microbial activity-low temperature, lack of nutrients, etc.-are removed (Kauppi et al 2011). Although BTEX (benzene, toluene, ethylbenzene, and xylenes) compounds, aromatic components of gasoline, are biodegradable, the removal efficiency is lower than for many of the aliphatic diesel fuel components (Soares et al 2010;Soares et al 2012). On the other hand, BTEX compounds are volatile and, similarly to the Volatile organic compounds (VOCs), can be easily removed by soil vapor extraction (SVE) if the conditions are suitable (Farhan et al 2001;Boudouch et al 2012).…”