When thyroid disease are treated with radio iodine (131J) in the nuclear medical department of hospitals, a large quantity of radioactive isotopes is deposited. The radioactive waste water may not be discharged into the public sewer, but must be stored until the radioactivity has decayed below the legally defined value.
Due to the long retention time of the waste water in the decay tank, an anaerobe process must be prevented to avoid bio-gas generation. And anaerobic process take place when the waste water is periodically aerated. Consequently, the hospital can abandon the neutralisation that was formerly used in decay plants