Design and test of an electro-bioreactor forthe bioremediation of PCBs in dredgedsediments

Details

Supervisors

Gerin

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en chimie et bioindustries, à finalité spécialisée

Abstract

PCBs are human-made persistent organic pollutants (POPs) that are harmful to humans and very difficult to biodegrade, and have therefore been banned from production worldwide since the 1980s. Nevertheless, many PCBs have accumulated in the sediments of estuaries and sea beds, and continue to pollute them today. This work is part of the GOLEM project, which aims at using the sludge of the Senne canal in Brussels for a revalorization in building material. To do so, it is necessary to remove PCBs and other organic matter from this polluted sludge of the canal.The aim of this master thesis is to set up an electro-bio-reactor for the biodegradation of PCBs in a complex medium such as the sludge of the Senne canal. Thus, we studied the degradation of PCBs catalyzed by microorganisms and by an electrode couple generating a redox gradient in the reactor. We started by working on the design of the reactor, to allow the sludge contained in the reactor to be resuspended and to make it pass from a reducing medium to an oxidizing medium. To do this, we first selected a fraction of the sludge that was settling more slowly. Then, we tried to gather this sludge in sedimentation above a source of H2 bubbles which, by rising to the surface, allowed the mixing of the sludge. Four reactors were launched over a period of nine weeks. These reactors were filled with the selected sludge as well as a small amount of raw sludge from the canal,serving as inoculum. The contents of these reactors were analyzed after 63 days of activity. These four reactors were used to test the effect on the polluted sludge of increasing the temperature from canal temperature to an ambient temperature of 21°C, the effect of H2 injection as well as the effectiveness of the presence of a pair of electrodes. Unfortunately, none of the four reactors showed significant PCB degradation. Nevertheless, they allowed us to highlight several areas of improvement for future work.In particular, the importance of maintaining relatively stable current and pH gradient, or even opening up a few possibilities to increase the quantity and activity of PCB-degrading microorganisms, such as the addition of primer.