BARC scientists recover uranium, cobalt-60 from nuclear waste

Use of radiation-resistant micro-organisms have enabled scientists of Bhabha Atomic Research Centre (BARC) to recover heavy metals like uranium and cadmium and radionuclides such as cobalt-60 from radioactive waste.

The treatment of these waste by microbes (both natural as well as genetically engineered ones) offers less expensive, eco-friendly, `in situ' (at the effluent site) alternative to the commonly used physiochemical methods of waste treatment, SK Apte, associate director, Biomedical Group and head, Molecular Biology Division, BARC said.

Nuclear waste contains a variety of heavy metals, radionuclides, organic solvents and other toxic substances and their management is a challenging task for scientists.

Deinococcus radiodurans, the most radioresistant bacterium known, has been genetically engineered at city-based BARC to scavenge Cobalt-60 and uranium from radioactive waste.

"Recovery of heavy metals and radionuclides from such wastes is desirable, not only to protect the environment but also to recover traces of precious metals such as uranium, which is not possible by conventional physiochemical process," Apte said.

Using a complex process, scientists produced recombinant strains of bacteria which could remove more than 90% of the heavy metal cadmium (used in alkaline batteries) and uranium in just 3 hours from very dilute solutions, he said.

"What's more, the deinococcus cells could do the job even after irradiation with very high doses of gamma rays, thereby demonstrating their ability to clean up radioactive waste of such metals.

Engineering the enzymes acid and alkaline phosphatases into microbes for bioprecipitation (deposition on microbes) of heavy metals holds promise for the development of appropriate technologies for recovery of uranium, cadmium and other metals from acidic, neutral and alkaline nuclear wastes, Apte said.

The use of such genetically engineered microbial cells offers an environmentally safe technology for bioremediation of cadmium, he said. "We are planning to extend this technology for removal of heavy metals from nickel-cadmium alkaline battery wastes in future."

Seawater is another vast source of uranium though the concentration of metal in seawater is just 3 ppb (3 micrograms per litre). These microbes can also be used for recovering heavy metals from seawater, the BARC official said.

However, BARC scientists are yet to work on microbial recovery procedures during an accidental situation like that at Japan's Fukushima power plant where radioactive wastes -metals such as caesium, tellurium, strontium and nonmetals like iodine - allegedly polluted the seawater from one of the damaged reactors.

"The possibility of recovering strontium, caesium and iodine using genetic engineering remains to be explored. Fukushima is a new, unexpected phenomenon of marine pollution and has to be studied in detail before coming out with appropriate solutions," Apte added.