Utilização de algoritmo genético para calibração de modelo de emissão de sulfeto de hidrogênio em estação de tratamento de esgoto com reator UASB e biofiltros aerados submersos

Abstract

Some wastewater treatment plants already have equipments and processes that reduce emissions of odorant gases, however, the population surrounding this type of plant can still be affected by it, due to the fact that human olfactory system is capable of perceiving the presence of odors in extremely low concentrations and short time interval.. The estimative of the odorant gases emission in WWTP can be obtained through mathematical models which involve a balance of mass in each of the WWTP units, where empirical equations simulate the physical, chemical and biological phenomena (volatilization, stripping, adsorption, absorption, biodegradation and chemical oxidation) responsible for the removal of the odorant gases dissolved in the wastewater mass. Lopes (2005) adapted an emission model in order to estimate concentration, removal and emission rates of H2S from a compact type of WWTP, composed by upward flow anaerobic digester (UASB) associated with a submerged aired biofilter (BF). In spite of the good results showed by adapted emission model, it was detected a need to calibrate it due to the use of empirical parameters obtained from other works that used other types of WWTP. The goal of this work is to calibrate the adapted and evaluated emission model by Lopes (2005) through the use of the genetic algorithm (AG) technique, responsible for reestimate some of the parameters associated with the empirical equations of the model. The results obtained showed that the parameters associated with the overall mass transfer between the gas phase and liquid phase decreased by around 25% after calibration; the parameter associated with the correction of oxygen to H2S increased by 66.6%, and the parameter associated with biodegradation (H2S removal of the liquid phase of BF) suffered no significant changes after the model calibration. The new estimates of the concentration of H2S in pumping station (EE) units, grid chamber (CA), UASB and BF were similar to the ones measured by Sá (2004), comparing to the concentrations estimated before the calibration of the emissions model, 0.51%, 0.25%, 0.29% and 1.96%, respectively. Regarding the estimated emission rates of H2S after the calibration of the emissions model, there was a reduction of 23% in EE, 11.6% in CA, 1.2% in the UASB, 10.5% in the CDV and 12.6% in BF, compared to the estimated emission rates before the calibration of the model.