Aplicação de traçador para caracterizar a influência da elevação da camada de lodo em lagoas facultativas

Abstract

Residence time distribution (RTD) is an essential tool for characterizing the hydrodynamical behaviors on non-ideal reactors, such as stabilization ponds used in wastewater treatment. Unlike ideal models of plugged or perfectly mixed flow, real reactors present complex behaviors due to stagnant zones (dead volume), recirculation, and hydraulic short circuits. The evaluation of the RTD allows the identification and quantification of these deviations, providing support for the diagnosis and optimization of system performance. In this study, the RTD for a prototype pond was investigated before and after simulating the formation of sludge bank, through experimental tests using sodium chloride as a tracer and monitoring the outlet electrical conductivity over time. From the data, two mathematical models were conceived, one using the classical method of matching moments and the other applying a numerical optimization tool through regression from the gamma distribution. The resulting data for the regression method showed an 𝑅2 coefficient slightly higher than the values obtained with the classical method for both experiments, indicating greater representativeness. The RTD resulting from the optimization method before the sludge bank simulation presented an average detention time of 1.09 days and a number of tanks of 1.84. After the simulation of sludge accumulation, the average time decreased to 0.58 days, where a reduction of 5.67 L in the effective volume for each liter of dead volume introduced was calculated. The number of tanks decreased to 1.62, indicating that after the sludge simulation the flow showed a tendency towards perfectly mixed flow.