Suitable real-time monitoring of the aerobic biodegradation of toluene in contaminated sand by spectral induced polarizationmeasurements and CO2 analyses

International audienceHydrocarbons commonly contaminate aquifers and, in certain cases, can be successfully treated through biodegradation. Biodegradation is an effective technique for cleaning up pollution by enhancing pollutant-degrading bacteria in situ. However, in situ sampling for monitoring processes occurring into the ground during the treatment is expensive and invasive. In this article, an alternative method was tested. Spectral Induced Polarization (SIP) was combined with gas analyses, CO2 concentration and its carbon isotopic ratio, to monitor toluene aerobic biodegradation in laboratory columns. Microbial activity was characterized by an evolution of the SIP response in correlation with a CO2 production with the same carbon isotope signature as toluene. The spectral induced polarization response followed the variations of bacterial activity and displayed a phase shift up to 15 mrad. These results support the feasibility of using geophysical measurements, supported by CO2 analyses, to monitor in situ hydrocarbon biodegradation, and they are proving to be highly promising for real field scale monitoring

Induced polarization applied to biogeophysics: recent advances and future prospects

This paper provides an update on the fast-evolving topic of the induced polarization (IP) method applied to biogeophysics. It emphasizes new understandings of the IP phenomena associated with biological activity, pointing out new developments and applications, and identifying existing knowledge gaps. The focus is on the use of IP as related to living organisms, including micro-organisms and plants (both roots and stems). We first discuss observed links between the IP signal and microbial cell structure, activity and biofilm formation. We provide an up-to-date conceptual model of the electrical behavior of the microbial cell and biofilm and examine the role of extracellular electron transfer mechanisms on the functionality and development of biofilms. We review the latest biogeophysical studies, including work on hydrocarbon biodegradation, contaminant sequestration, soil strengthening and peatland characterization. We then elaborate on the IP signature of the plant root zone, relying on a state-of-the-art conceptual model of the biogeophysical mechanisms of a plant root cell. The first laboratory surveys show that single roots and root system are highly polarizable. They also present encouraging results for imaging the root system embeded in a medium and gaining information on the mass density, the structure or the physiological characteristics of the root system. IP is also used to characterize wood and tree structures in the lab but also at the field scale, through tomography of the stem. Finally, we discuss up- and down-scaling between lab and field studies as well as joint interpretation. We emphasize the need for intermediate scale studies and the benefits of using IP as a time-lapse monitoring method. We conclude with the promising integration of IP in global mechanistic models to better understand and quantify subsurface biogeochemical processes