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.