Wet deposition and soil content of Beryllium - 7 in a micro-watershed of Minas Gerais (Brazil).

Beryllium-7 (7Be) is a natural radionuclide of cosmogenic origin, normally used as a tracer for several environmental processes; such as soil redistribution, sediment source discrimination, atmospheric mass transport, and trace metal scavenging from the atmosphere. In this research the content of 7Be in soil, its seasonal variation throughout the year and its relationship with the rainfall regime in the Mato Frio creek micro-watershed was investigated, to assess its potential use in estimating soil erosion. The 7Be content in soil shows a marked variation throughout the year. Minimum 7Be values were observed in the dry season (from April to September) and were between 7 and 14 times higher in the rainy season (from October to March). The seasonal oscillations in 7Be soil content could be explained by the asymmetric rainfall regime. A highly linear relationship between rainfall amount and 7Be deposition was observed in rain water. A good agreement between 7Be soil content and 7Be atmospheric deposition was noticed, mainly in wet months. 7Be penetration in soil reaches a 5 cm depth, this could be explained by the soil type in the region. The soils are Acrisol type, characterized by low pH values and clay illuviation in deeper layers of the soil. In some regions of Brazil special attention should be paid if this radionuclide will be used as soil erosion tracer, taking into account the soil origin and its particular properties.

Influence of inlet positions on the flow behavior inside a photoreactor using radiotracers and colored tracer investigations.

The influence of the inlet positions on the flow behavior inside a photoreactor has been studied using colored tracer and radiotracer investigations. The photoreactor for water disinfection is a tubular reactor inside which UV emitting lamps are placed. The key to its good performance is a combination of optimum irradiation dose and fluid residence time distributions (RTD). The inlet system is one of the better possibilities of controling the fluid RTD. Three configurations have been tested. In the first step, colored tracer experiments help us to raise the mean trends of the flow behavior for the different configurations. When the inlet is located at the central bottom of the reactor, the flow is closed to a perfect mixing whereas lateral inlets lead to a plug flow with axial dispersion behavior. RTD measurements using radiotracer was carried out in a wide range of flowrates. The axial dispersion coefficient increases linearly with the Reynolds number. It is lower when the lateral inlet is divided in three inlets uniformly distributed around the bottom of the reactor. This paper shows the usefulness of radioactive isotopes as tracers in the field of wastewater treatment.