Distribuição do gás ozônio em milho armazenado em silo metálico usando sistema de aeração

• Autor(a) principal: Rozado, Adriano Ferreira
• Data de Publicação: 2013
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/746
• topic: Distribuição do gás ozônio; Borbulhamento; Análise de regressão; Ozone gas distribution; Bubbling; Rression analysis; CNPQ::CIENCIAS AGRARIAS::ENGENHARIA AGRICOLA::ENGENHARIA DE PROCESSAMENTO DE PRODUTOS AGRICOLAS::PRE-PROCESSAMENTO DE PRODUTOS AGRICOLAS

This work aimed to evaluate the distribution of ozone gas at different positions in the mass of grain subjected to ozonization processes with and without residual ozone recirculation, as well as to evaluate the physical and physiological qualities of maize grains subjected to these two processes. Maize grains with water content around 12.5% (wb) were packed in a metallic silo with diameter of 0.60 m, height of 3.0 m, equipped with exhaustion and gas recirculation devices. A metallic bottom was placed at a distance of 0.26 m from the silo base, with 25% drilling to hold the grains and form a plenum chamber to the air/ozone mixture insufflation. To evaluate ozone distribution, 0.04 m diameter and 0.30 m length PVC probes were built. These probes were arranged in six 0.5 m equidistant points along the grain column, from which ozone samplings were collected at regular intervals of 1.0 h, as well as in a point located in the plenum chamber and another above the 3.0 m grain column to determine the entrance and residual concentrations, respectively. The ozonization systems worked continuously, injecting the air/ozone mixture during a period of 148 h. The sample-collecting procedures and ozone concentration quantification consisted of gas bubbling in potassium iodide solution during one minute, followed by titration with sodium thiosulfate solution. The ozone produced by the generator was injected in the plenum chamber through a connection placed on the silo s base, and the air/ozone mixture was inflated on the grain mass under specific flow of 1.0 m3 min-1 t-1, at mean concentrations of 622.1 and 494.2 ppm (1.33 and 1.06 g m-3), with and without recirculation of residual ozone, respectively. To evaluate the effect of ozone concentration levels on the physical and physiological qualities of the maize grains, water content, specific mass, germination potential and electrical conductivity tests were carried out. Grain mass temperature, air/ozone mixture temperature in the plenum, temperature and relative air humidity before passing through the ventilator and air/ozone mixture temperature after passing through the grain mass were monitored and recorded by a data acquisition and storage system named 1-wire, using temperature (DS18B20) and relative humidity (DS2438) sensors. The temperature of the grain mass subjected to the ozonization process with recirculation was, on average, 2.0 oC superior to that of the grains subjected to the process without recirculation. The ozone concentration quantification data were submitted to regression analyses and, based on the coefficient of determination,the models of ozone gas distribution in the grain mass and of the residue released were adjusted by means of the Sigmaplot software. The evaluation data obtained on the physical and physiological qualities of the grains subjected to the ozonization processes were compared to the control sample data, applying the Dunnett test at 5% probability using the Saeg software. It was concluded that the adjusted mathematical model representing the ozone gas distribution process in the maize grain mass was the one of Chapman-Richards, three-parameter sigmoidal asymptotic, regardless of the ozonization process. We also noted that, the closer to the point of ozone gas injection, the greater the concentration level is, and the shorter the ozone stabilization time is, regardless of the type of ozonization process, with or without residual ozone recirculation. The highest asymptotic value achieved by the ozone concentration is 425.89 ppm (0.912 g m-3) for the 0.5 m grain column without residual ozone recirculation. The lowest asymptotic concentration possible in the maize grain mass was 180.1 ppm (0.386 g m-3) when located 3.0 m from the insufflation point (plenum), without residual ozone recirculation. In general, the shortest estimated times needed to obtain the desired local concentration were achieved through the ozonization process with residual ozone recirculation. The shortest estimated time to obtain the concentration of 50 ppm (0.107 g m-3) was 1.1 h, with residual ozone recirculation for a 0.5 m grain column. The longest estimated time to achieve 50 ppm of ozone was 46.9 h, without residual ozone recirculation, for grains located 3.0 m from the point of insufflation of the air/ozone mixture. In general, the ozone insufflation processes in the grain mass do not affect the physiological quality of the maize grains, regardless of the position and ozonization process. However, there was a reduction in the final water content of 0.7% and 1.0% in grains subjected to ozonization processes with or without recirculation of residual ozone, respectively, due to the environmental conditions involved in the processes. Therefore, the two ozonization processes studied in this work, with and without recirculation of residual ozone, permit to obtain ozone concentrations in the grain mass capable of controlling pests found in stored maize in periods shorter than 148 h.