Evaluation of the potential of biodegradation for the disposal of cutting fluid from the machining of uranium

The disposal of used cutting fluid from the machining of uranium is problematical. Biodegradation offers the potential to convert this material into forms amenable to disposal as low level radioactive waste. The real bonus of biodegradation for radioactive applications crucially depends on the degree of mineralisation achieved. In non-radioactive trials using a consortium of bacteria selected from used cutting fluid, only 33% of the organic carbon was converted to carbon dioxide, even though 90% of the principal component (hydrocarbons) was biodegraded. Intermediate degradation products (identified as naphthenic acids) accumulated. Downstream processing of the biotreated fluid by ultrafiltration and adsorption onto activated charcoal produced a waste stream that would qualify as aqueous radioactive waste. Separated biomass was immobilised in a cement matrix that would qualify as solid radioactive waste, albeit in a volume which would make the overall process inefficient. Future work to optimise the process is proposed.