Ph. D. Camille SECHER

Development of a treatment process for soils and sediments polluted by polychlorinated biphenyls by coupling bioaugmentation/ phytoremediation.

Defended in June 2012,

Under the supervision of Thierry Lebeau

Co-supervision: Karine JEZEQUEL and Marc LOLLIER

Abstract

Polychlorinated biphenyls (PCBs) are persistent organic pollutants synthesized and used for many industrial applications (hydraulic fluids, plasticizers…) until the 1970s. These compounds are widespread in natural environments, particularly in soils and sediments, and accumulate there due to their particular chemical properties. They thus represent a danger for the environment and for humans because of their high chronic toxicity.

The decontamination of environments polluted by these PCBs is therefore necessary. Physical-chemical processes, although effective, have the disadvantage of being very costly in terms of energy and money. Biological treatments are an ecological and cheap alternative to physical-chemical methods. Indeed, PCBs can be degraded by certain bacteria according to two different metabolic pathways depending on the oxygenation conditions of the environment: oxidative degradation under aerobic conditions and reductive dechlorination under anaerobic conditions. The association of a PCB degrading bacterium and a plant stimulating the growth and the bacterial activity seems to be appropriate to improve and stabilize the in-situ treatments of polluted soils.

The objective of this thesis work was to develop a treatment process for PCB polluted soils by coupling bioaugmentation and phytoremediation. For this, a bacterium was selected (Burkholderia xenovorans LB400) for its degradation capacities and the culture conditions of this strain before inoculation in the soil were determined. The survival of a bacterium inoculated in a matrix such as soil being a critical step, the quantitative PCR method specific to B. xenovorans LB400 was developed to confirm its presence over time. In parallel, the selection of plants, based on their growth and the development of their root system in the soil to be decontaminated, made it possible to choose the fescue (Festuca arundinacea) for the continuation of the work. Finally, the degradation performance of PCBs present in the soil was evaluated during two months, by bioaugmentation of the soil by the LB400 bacterium, associated or not with fescue. The impact of soil inoculation with LB400 bacteria and/or fescue on the soil bacterial microflora (quantity and structure) was evaluated.