Association of naturally occurring radionuclides in sludges from Drinking Water Treatment Plants previously optimized for their removal.
The raw water used in Drinking Water Treatment Plants (DWTPs) can present high values of naturally occurring radionuclides. In order to reduce this content, the routine working conditions of DWTPs were successfully modified. This meant that those radionuclides were accumulated in the sludges generated, whose radioactive content was frequently above the exemption levels. It therefore becomes necessary to assess the association of naturally occurring radionuclides in the sludges for their potential use as agricultural fertilizers. Two approaches were studied: (a) the effect of different sequential extraction methods applied to a selected sludge; and (b) the effect of the different contents of inorganic complexes dissolved in the input water on the composition of the sludges generated by two DWTPs with different origins of their input water. Uranium and radium were mainly associated with the carbonated and reducible fractions, while (210)Po and (228)Th were associated with the residual fraction. There were differences between the two speciation methods, but the order of bioavailable radionuclides was roughly the same: (226)Ra≈(234,238)U>(228)Th>(210)Po. The major inorganic complexes content, mainly carbonate, in the raw water affected the radionuclide association. The greater the carbonate content in the raw water, the greater was the association of uranium and radium with the carbonated and easily reducible fractions.
LARUEX, Environmental Radioactivity Laboratory, Dpt. Applied Physics, Faculty of Veterinary Sciences, Avda. Universidad, s/n, 10003 Cáceres, Spain.
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Baeza
LARUEX, Environmental Radioactivity Laboratory, Dpt. Applied Physics, Faculty of Veterinary Sciences, Avda. Universidad, s/n, 10003 Cáceres, Spain.
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Salas
LARUEX, Environmental Radioactivity Laboratory, Dpt. Applied Physics, Faculty of Veterinary Sciences, Avda. Universidad, s/n, 10003 Cáceres, Spain. Electronic address: fguillen@unex.es.
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Guillén
LARUEX, Environmental Radioactivity Laboratory, Dpt. Applied Physics, Faculty of Veterinary Sciences, Avda. Universidad, s/n, 10003 Cáceres, Spain.
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Muñoz-Serrano
D005308:Fertilizers; D011834:Radiation Monitoring; D011868:Radioisotopes / Q000032:analysis*; D011883:Radium / Q000032:analysis; D012722:Sewage / Q000737:chemistry; D014501:Uranium / Q000032:analysis; D014875:Water Pollutants, Radioactive / Q000032:analysis*; D018508:Water Purification / Q000379:methods*
D005308:Fertilizers; D011868:Radioisotopes; D012722:Sewage; D014875:Water Pollutants, Radioactive; D014501:Uranium; D011883:Radium
DWTP; NORM; Radium; Sludge; Speciation; Uranium