RESUMEN

Samples were collected for several weeks to determine the evolution of the 131I (Iodine-131) activity concentration in the inflow water processed at the Salitre wastewater treatment plant (WWTP) in Bogota, Colombia, derived from medical facilities for thyroid cancer diagnosis and treatment. Mass balances on 131I were performed based on the activity rates at the main inflow and outflow of the plant. The 131I activity concentration in the raw water stream was observed to increase significantly from Monday onwards throughout the week, while the daily activity concentration was highest in the morning and then continuously decreased over the rest of the day. The 131I activity concentration in the raw water exceeds the reference value for drinking water and is very close to the discharge limit in water bodies in Colombia. A mass balance calculation showed that the activity rate for the inflow and outflow waters of the WWTP is about 15% of the authorized activity to use for facilities discharging water into the basins and the use of bio-sludge stream for organic fertilizer production does not represent a significant risk of external irradiation for the population. The results of this work are the first of its kind in Colombia, which ones contribute significantly to determinate the radiological risk to public health due to utilization of treated water and sludge, know the 131I behavior in the city sewage systems, and give information for the performance review of regulatory control on 131I management in the country.

Asunto(s)

RESUMEN

Three methods of molecular dynamics simulation [Green-Kubo (G-K), non-equilibrium molecular dynamics (NEMD) and reversed non-equilibrium molecular dynamics (RNEMD)], and two group contribution methods [UNIFAC-VISCO and Grunberg-Nissan (G-N)] were used to calculate the viscosity of mixtures of n-heptane and toluene (known as heptol). The results obtained for the viscosity and density of heptol were compared with reported experimental data, and the advantages and disadvantages of each method are discussed. Overall, the five methods showed good agreement between calculated and experimental viscosities. In all cases, the deviation was lower than 9%. It was found that, as the concentration of toluene increases, the deviation of the density of the mixture (as calculated with molecular dynamics methods) also increases, which directly affects the viscosity result obtained. Among the molecular simulation techniques evaluated here, G-K produced the best results, and represents the optimal balance between quality of result and time required for simulation. The NEMD method produced acceptable results for the viscosity of the system but required more simulation time as well as the determination of an appropriate shear rate. The RNEMD method was fast and eliminated the need to determine a set of values for shear rate, but introduced large fluctuations in measurements of shear rate and viscosity. The two group contribution methods were accurate and fast when used to calculate viscosity, but require knowledge of the viscosity of the pure compounds, which is a serious limitation for applications in complex multicomponent systems.