The removal of radionuclides during desalination of geothermal waters containing boron using the BWRO system

Abstract

In this study, the effect of the removal of radionuclides from geothermal water containing boron was investigated using a two-pass reverse osmosis system for brackish water desalination (BWRO). The determination of the total α and β activity levels, concentrations of tritium, radon (222Rn), uranium (238U, 234U) and radium (226Ra, 224Ra) isotopes and annual effective dose equivalents were calculated taking into account the age dependent dose factors and concentrations of radionuclides in permeate. The concentrations of radioactive substances in the product water were much lower than in the feed water. The rejection rate ranged from 70.7% for both radium isotopes to not less than 77.2% for uranium. The gross α and β activities in permeate were too low to quantify, so the rejection rates were also high, not less than 72.9%. The research identified no dependency between radionuclide rejection and mineral content.The annual effective dose rate resulting from the consumption of the treated geothermal waters investigated, and calculated from the uranium and radium isotopes present, does not exceed the recommended value of 0.1mSv/year for adults and children in all cases. However, assuming a consumption of 250L of water in infants (below one year of age) and higher committed unit doses in this age group, the average effective dose equivalent from radionuclides would have been exceeded by a factor of 3 to 4.