Adaptation of Working Conditions of an Operating Drinking Water Treatment Plant to Remove Naturally Occurring Radionuclides

摘要

Naturally occurring radionuclides such as uranium and radium are present in water used for human consumption. There are several procedures to remove the uranium and/or radium content in drinking water, although they have mainly been used just in laboratory tests, and in only a few cases in pilot plants. In the present work, an operating drinking water treatment plant (DWTP) with gross alpha activity above the 0.1 Bq L~(-1) threshold was selected, with the water's uranium content being principally responsible for this activity. The routine procedure used in the DWTP was incapable of removing this activity from the drinking water. A modification of the procedure in the coagu-lation-flocculation step successfully removed 50-83 % of the uranium from the drinking water finally consumed by the population, with the resulting gross alpha activity being reduced to below 0.1 Bq L~(-1). The modified procedure was reversible-whenever the procedure was halted, no uranium was removed. The uranium removed ended up concentrated in the sludge generated by the plant. A sequential extraction procedure applied to the sludge showed most of it to be attached to the easily and moderately reducible frac- tions and hence extractable with hydroxylamine and ammonium oxalate, respectively. This was because in the coagulation-flocculation process, the uranium was essentially removed by association with aluminium oxides.