Estudo experimental de transferência de massa entre as fases líquida e gasosa no interior de um túnel de vento portátil utilizado para estimativa das taxas de emissão para compostos odorantes.

Abstract

Wastewater treatment plants and landfills are major sources of odor in urban environments and, despite not being necessarily associated with toxic and harmful effects on human health, this pollutant causes annoyance. In wastewater treatment plants, the presence of liquid passive emission sources is common, where the direct method is one of the ways to quantify emissions from these sources. The portable wind tunnel is one of the devices applied in the direct method and this is characterized by the incidence of a carrier gas on the liquid surface through a flow parallel to the surface, however, this equipment is not capable of simulating all the significant phenomena for mass transport. Thus, mass transfer studies between the liquid-gas interface are extremely important to understand the behavior of this device. Therefore, this work aims to study the mass transfer at the liquid-gas interface inside the portable wind tunnel used to estimate the emission rates of volatile odorant compounds from passive liquid surfaces through the spectrophotometry technique. The results showed that, for hydrogen sulfide, the global mass transfer coefficient (KL) did not change with different flow rates due to the non-disturbance of the liquid phase, and it obtained an average value of 2,48×10-5 m s-1. No variation of KL was noticed between the 6 sample points analyzed. When compared with field situations, which were represented by the model proposed by Prata et al. (2018), the tunnel represented the same mass flow for wind speeds of 5.85, 6.07 and 7.12 m s-1 for upstream relative roughness of, respectively, 0.005.0 .01 and 0.1 "m", considering the effective length of 50 m. As for the effective length of 300 m, there was less influence of the relative roughness upstream, where the same respective roughness provided the same measured flow in the tunnel for wind speeds of 5.30, 5.34 and 5.26 m s-1. The experimentally estimated coefficients (KL) were compared with the empirical models present in the literature considering the flow conditions applied in the laboratory. Therefore, it was found that the portable wind tunnel, when compared with these models, overestimates the emission between 4.8 and 17.5 times. When comparing the values presented in this work with the experimental data obtained by Santos et al. (2012), the overestimation caused by the portable wind tunnel is also noted. It was not possible to analyze n-butanol and acetic acid by the proposed methodology