Biological remediation and removal of radioactive metals and complex aromatic compounds from nuclear and radioactive waste

Abstract

In pursuing carbon emission free technologies in the energy industry, interest in nuclear energy has grown. However, technology for handling radioactive waste containing organic materials are lacking. Methods are required for biodegradation of often recalcitrant irradiated organic compounds which are persistent in radioactive waste from the nuclear industry. In this study, a bioseparation process for extraction of 14C and de-radiation of nuclear graphite was investigated in a continuous flow sequencing-batch/biofilm reactor. Dehalogenation and mineralisation of aromatic halogenated compounds in the waste stream of a pebble bed manufacturing process was simulated by the photocatalytic/biological hybrid system in the 50 to 1,000 4-CP mg.L-1. The efficiency of degradation of the irradiated compounds was compared to conventional degradation using PAH degrading microorganisms. The Pathway of degradation was established for both systems by evaluating the intermediates of degradation of radiolabelled phenolic compounds with ortho-13C-ortho and para-13C phenol. Phenol degradation under photocatalytic conditions was shown to follow the catechol hydroquinone hydroxyhydroquinone benzene-1,2,3-triol pathway, whereas the degradation in the biological stage followed the meta-cleavage pathway via catechol 2-hydromuconic semialdehyde pyruvate under aerobic conditions. This study demonstrates the potential of efficiently managing the organic component of nuclear waste using a cleaner, environmentally friendly biological process.