The investigation of the limiting factors for the bioremediation of PCBs in dredged sediments

Details

Supervisors

Gerin, Patrick A.

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en sciences agronomiques, à finalité spécialisée

Abstract

Polychlorinated biphenyls (PCBs) are persistent organic pollutants (POP’s). They are human-made organic chemicals that where produced and used from the 1930s to the 1970s. The stable properties of these compounds led to their widespread accumulation in the environment, and to growing concerns about the effects of these environmental contaminants on the health of humans and wildlife. Therefore, they have been banned from production since the 1980s. However, these compounds are very stable and poorly degradable, so they have been accumulated in the environment and are still present. This Master's thesis is part of the GOLEM project, which aims to remove organic contaminants, persistent organic pollutants including PCBs from sludge sediments from the Senne canal. All these contaminants as well as the organic matter prevent the valorization of the sludge and therefore require decontamination. PCBs must be degraded by microorganisms that are naturally present in the sludge. The development of an in-situ treatment solution that uses microbial activity, could potentially reduce high costs and negative environmental impacts associated with the widely applied technologies for treating PCB-impacted sites such as dredging and capping. The goal of this project is to provide a systematic strategy to find economically viable valorization routes for urban sediments. The aim is to recycle this sludge into unfired building bricks. The objective is to design a reactor that can decontaminate these sediments using a green, electro- bio-catalyzed approach, while also lowering their organic content and allowing them to be recycled without leaving behind undesired chemical residues. Therefore, we analyzed the reductive dechlorination reaction of PCBs by microorganisms under anaerobic conditions, as well as the identification of the key limiting factors. We launched 21 reactors with 7 different major conditions. These reactors contained a quantity of the fraction selected from the canal sludge that settles more slowly and allows to be well suspended in the reactors. Then the different parameters tested were the addition of different amounts of inoculum which is fresh canal sludge, the addition of sodium acetate and the addition Aroclor1232. Unfortunately, we found no evidence of PCBs biodegradation in our bioreactors. However, our work has allowed to highlight new hypotheses and perspectives for future experiments. In particular, the hypothesis that PCBs may be trapped in the micropores of the particles and therefore inaccessible to the microorganisms. Our work even opens up other possibilities to stimulate or increase the amount of PCB-degrading microorganisms through bioaugmentation or primers.