Radiotracer investigation in an aerobic digester of a wastewater treatment plant

Radiotracer residence time distribution (RTD) methodology was used to determine the hydrodynamic parameters of the aerobic digester of an effluent treatment plant. Technicium-99m was used as a radiotracer. The concentration of radiotracer in the exit stream of the digester was determined using an on-line tracer monitoring method. The experimental mean residence time (MRT) of the digester was found to be 4 h, far less than the theoretical MRT calculated with respect to nominal flow parameters (volume and flow rate of material into the digester). The experimental MRT corresponds to a percentage effective volume of 11% translating into approximately 89% dead volume in the digester leading to the conclusion that the hydrodynamic performance of the aerobic digester of the effluent treatment plant was not efficient. A radioactive tracer (Tc-99m) was used to determine the flow type in the digester; an RTD Software was used to model the flow by curve fitting the experimental RTD with various non ideal flow models. It was observed from the radiotracer experiment that the perfect mixers in series with exchange model best described the flow type existing in the digester.