Denim production is one of the leading sub-sectors of textile industry which basically generates highly colored indigo dyeing effluents. In the present study, ozonation was applied to the indigo-dyeing effluent(COD=820 mg/L / color=5500 Pt-Co), and to the whole effluent from a denim-producing plant before(COD=2750 mg/L / color=3950 Pt-Co) and after(COD=800 mg/L,color=3700 Pt-Co) biological treatment for degradation/detoxification purposes. Ozonation was also tried in the wastewater of the plant(COD=3100 mg/L / color=4500 Pt-Co) that would be produced after some foreseen cleaner production measures / caustic recovery and reusing of dyeing process wastewater. When applied to indigo-dyeing wastewater / ozonation provided 95% color and 61% COD removals at 1320 mg/h ozone dose within 60 minutes The optimum pH was evaluated as 4 when indigo-dyeing wastewater exposed to ozonation at different pHs(1.6-12.3). On the other side, ozonation applied as pre-treatment to the plant effluent provided 86% color and 46% COD removals with 3240 mg/h ozone dose in 70 minutes. Less satisfactory results were obtained when ozonation was tried in the wastewater after measures, with 86% color and 31% COD removals at 3960 mg/h ozone dose in 80 minutes. When applied to the biologically-treated effluent / at 420 mg/h ozone dose and within 40 minutes, ozonation removed 47% of influent COD and 96% of influent color indicating better performance of ozonation in postoxidation. In order to assess possible improvements on ozonation with the addition of H2O2, different concentrations were tried, but no significant improvement was obtained. The improvement in BOD5/COD index was also determined for the ozonetreated plant effluent to measure the effects of ozonation on biodegradability and found out that BOD5/COD ratio has improved to 0.39 from 0.22.

Textile wastewaters are highly colored and non-biodegradable having variable compositions of colored dyes, surfactants and toxic chemicals. Recently, ozonation is considered as an effective method that can be used in the treatment of industrial wastewaters / catalytic ozonation being one of the advanced oxidation processes (AOPs), is applied in order to reduce the ozone consumption and to increase the chemical oxygen demand (COD) and total organic carbon (TOC) removals. In this study, catalytic ozonation of industrial textile wastewater (ITWW) obtained from AKSA A.S. (Yalova, Istanbul) textile plant has been examined in a three phase fluidized bed reactor at different conditions. The effects of inlet chemical oxygen demand concentration (CODin), pH, different catalyst types [perflorooctyl alumina (PFOA) and alumina] and catalyst dosage on ozonation process were determined. Moreover, the changes in the organic removal efficiencies with gas to liquid flow rate ratio were investigated. The dispersion coefficients (DL) and volumetric ozone-water mass transfer coefficients (kLa) were estimated at various gas and liquid flow rates in order to observe the effect of liquid mixing in the reactor on ozonation process. It was observed that increasing both gas and liquid flow rates by keeping their ratio constant provided higher organic removal efficiencies due to the higher mixing in the liquid phase. The dyes present in ITWW sample were known to be Basic Blue 41 (BB 41), Basic Red 18.1 (BR 18.1) and Basic Yellow 28 (BY 28). The &ldquo / absorbance vs. concentration&rdquo / calibration correlations were developed to estimate the amounts of these colored dyes in the ITWW sample. This provided the opportunity to examine the degradation of each dye in this wastewater separately. While PFOA catalyst was found to increase the removal efficiency of BY 28 at an acidic pH of 4, alumina yielded highest color removals for BB 41 and BR 18.1 at a pH of 12. The highest TOC and COD reductions being 24.4% and 29.5%, respectively, were achieved in the catalytic ozonation of the ITWW using alumina as the catalyst at a pH of 12 and at a gas to liquid flow rate ratio of 1.36 (QG = 340 L/h, QL = 250 L/h). At the same conditions, also the highest overall color removal in terms of Pt-Co color unit, namely 86.49%, were obtained due to the lower BY 28 concentration in the WW sample than those of the BB 41 and BR 18.1. In addition, the oxidation of BB 41, BR 18.1 and BY 28 dyes were investigated in a semi-batch reactor by sole and catalytic ozonations with alumina and PFOA catalyst particles. The sole and catalytic ozonation reactions followed a pseudo-first order kinetics with respect to dye concentration. The highest TOC and COD removals being 58.3% and 62.9%, respectively, were obtained at pH of 10 for BB 41 and 55.2% and 58.8%, respectively, for BR 18.1 with alumina catalyst. On the other hand, for BY 28 PFOA catalyst yielded highest TOC and COD reductions being 61.3% and 66.9%, respectively, at pH of 4.

Environmental regulations have imposed limitations on a wide variety of organic and inorganic pollutants in industrial textile wastewaters. There are several degradation methods used in literature studies. Among these methods ozonation is one of the most considered way to degrade refractory chemicals in textile wastewaters. In recent years, catalytic ozonation as being one of the advanced oxidation processes (AOPs), is applied to reduce the ozone consumption and to increase the Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) removals. Ozonation and catalytic ozonation of single and mixed dye solutions have been examined both in a semi-batch reactor and also in a three phase fluidized bed reactor. The dyes that are used in this study are Basic Blue 41 (BB-41), Basic Yellow 28 (BY-28) and Basic Red 18.1 (BR-18.1), these dyes are obtained from AKSA A.S. (Yalova, Istanbul) textile plant. In order to measure the concentration of each dye in the mixed dye solution, &ldquo / absorbance vs. concentration&rdquo / calibration correlations were developed. The effect of inlet dye concentration, inlet gas and liquid flow rates, pH, catalyst type [perflorooctyl alumina (PFOA) and alumina] and catalyst dosage were determined experimentally. Catalyst characterization analyses were done in order to determine the maximum number of times that the catalyst can be used and it was found to be 3 times. Gas washing bottle experiments are conducted to find the v amount of ozone required to oxidize one mole of each dye used in the study. Oxidation of BB-41, BR-18.1 and BY-28 dyes were investigated in a semi-batch reactor as single dye solutions by sole and catalytic ozonation with alumina and PFOA catalyst particles. The highest TOC and COD removals being 58.3% and 62.9%, respectively, were obtained at pH of 10 for BB-41 and 55.2% and 58.8%, respectively, for BR-18.1 with alumina catalyst. On the other hand, for BY-28 PFOA catalyst yielded highest TOC and COD reductions being 61.3% and 66.9%, respectively, at pH of 4. Minimum fluidization velocity (uL,min), the hold-up values of gas, liquid and solid phases, the dispersion coefficients (DL), and volumetric ozone-water mass transfer coefficients (kLa) were estimated at various gas and liquid flow rates in order to observe the effect of liquid mixing in the reactor on ozonation process. While PFOA catalyst was found to be effective in oxidizing BY-28 in acidic conditions (pH=4), BR-18.1 and BB-41 are degraded in alkaline medium (pH=10) with alumina catalyst better compared to acidic conditions. For catalytic ozonation reactions in fluidized bed reactor, the highest dye removals in mixed dye solution were observed for BY- 28 being 99.29% for gas flow rate (QG) of 340 L/h, liquid flow rate (QL) of 150 L/h and pH=4, initial dye concentration being 30 mg/L of each dye with PFOA catalyst, while for BR-18.1 and BB-41 being 95.39% and 97.95% respectively for QG = 340 L/h, QL = 150 L/h and pH=10, initial dye concentration being 30 mg/L of each dye with alumina catalyst. The highest TOC and COD reductions, 25.2% and 32.4%, respectively, were achieved in the catalytic ozonation of the mixed dye using PFOA as the catalyst at a pH of 4 and at a gas to liquid flow rate ratio of 2.26 (QG = 340 L/h, QL = 150 L/h). Highest dye removals were obtained at the same gas and liquid flow rates as those of the highest TOC and COD reductions in the experiments. Empirical TOC removal equations were obtained as a function of inlet TOC concentration, solution pH, gas and liquid flow rates.

Ο στόχος την παρούσας εργασίας είναι η αποδόμηση των PAHs με χρήση όζοντος.Για το σκοπό αυτό επιλέξαμε το φαινανθρένιο ως ένωση-μοντέλο σε οργανικό διαλύτη, με απώτερο στόχο την επεξεργασία επικίνδυνων αποβλήτων. / The perpose of this study is the degradation of polycyclic aromatic hydrocarbons with ozon. For this reason we use phenanthrene like model-compound in organic solution.

De nombreuses études ont déjà été faites sur le noir de carbone et sur son oxydation soit par l'acide nitrique, soit par l'ozone. Mais les oxydations ont généralement été poussées à un degré tel que la particule était partiellement détruite : la perte de masse atteignait jusqu'à 50 %, la dimension des granulés diminuait sensiblement et le réseau lui-même était nettement modifié. Le but de notre étude a été de savoir s'il était possible de rendre les particules hydrophiles par oxydation superficielle ménagée tout en en modifiant le moins possible la structure interne. Or il était difficile de modérer suffisamment l'oxydation d'une poudre en opérant par voie sèche, c'est pourquoi nous avons fait agir un oxydant gazeux, à savoir: l'ozone qui était tout indiqué, en milieu aqueux, les granules de noir étant maintenus en suspension par une agitation mécanique à l'aide d'un vibreur. Chaque particule étant ainsi recouverte d'une couche lamellaire d'eau lui servant d'écran, se voyait soumise, d'une façon très douce, à l'action de l'ozone. Notre étude comprend donc les parties suivantes : Ozonisation, granulométrie, étude par diffraction X, acidité totale. Nous pouvons affirmer qu'une oxydation par l'ozone en milieu aqueux rend le noir de carbone hydrophile par fixation de groupes superficiels COOH sans modifier sensiblement la granulométrie ni la structure interne aux rayons X.

The effectiveness of partial ozonation of return activated sludge for enhancing denitrification and waste sludge minimization were examined. A pair of nitrifying sequencing batch reactors was operated in either aerobic or alternating anoxic/aerobic conditions, with one control and one ozonated reactor in each set. The amount of solids decreased with the ozone dose. Biomass in the anoxic/aerobic reactor was easier to destroy than in the aerobic one, generating approximately twice as much soluble chemical oxygen demand (COD) by cell lysis. Increased COD favoured production of extracellular polymers in ozonated reactors, enhancing flocculation and improving settling. Floc stability was also strengthened in prolonged operation in alternating treatment, resulting in declined solids destruction. Dewaterability was better in alternating reactors than in aerobic ones indicating that incorporation of an anoxic zone for biological nutrient removal leads to improvement in sludge dewatering. The negative impact of ozonation on dewaterability was minimal in terms of the long-term operation. Ozone successively destroyed indicator estrogenic compounds, contributing to total estrogen removal from wastewater. Denitrification rate improved up to 60% due to additional carbon released by ozonation. Nitrification rates deteriorated much more in the aerobic than in the alternating reactor, possibly as a result of competition created by growth of heterotrophs receiving the additional COD. Overall, ozonation provided the expected benefits and had less negative impacts on processes in the alternating treatment, although after prolonged operation, benefits could become less significant. The alternating anoxic/aerobic reactor achieved twice the nitrification rates of its aerobic counterpart. Higher removal rates of estrogens were associated with higher nitrification rates, supporting the contention that the nitrifying biomass was responsible for their removal. The alternating treatment offered the better estrogen biodegradation. Microbial populations in both reactors were examined with fluorescent in situ hybridization. Dominance of rapid nitrifiers like Nitrosomonas and Nitrobacter (79.5%) in the alternating reactor, compared to a dominance of slower nitrifiers like Nitrosospira and Nitrospira (78.2%) in the aerobic reactor were found. The findings are important to design engineers, as reactors are typically designed based on nitrifiers’ growth rate determined in strictly aerobic conditions.

The effectiveness of partial ozonation of return activated sludge for enhancing denitrification and waste sludge minimization were examined. A pair of nitrifying sequencing batch reactors was operated in either aerobic or alternating anoxic/aerobic conditions, with one control and one ozonated reactor in each set. The amount of solids decreased with the ozone dose. Biomass in the anoxic/aerobic reactor was easier to destroy than in the aerobic one, generating approximately twice as much soluble chemical oxygen demand (COD) by cell lysis. Increased COD favoured production of extracellular polymers in ozonated reactors, enhancing flocculation and improving settling. Floc stability was also strengthened in prolonged operation in alternating treatment, resulting in declined solids destruction. Dewaterability was better in alternating reactors than in aerobic ones indicating that incorporation of an anoxic zone for biological nutrient removal leads to improvement in sludge dewatering. The negative impact of ozonation on dewaterability was minimal in terms of the long-term operation. Ozone successively destroyed indicator estrogenic compounds, contributing to total estrogen removal from wastewater. Denitrification rate improved up to 60% due to additional carbon released by ozonation. Nitrification rates deteriorated much more in the aerobic than in the alternating reactor, possibly as a result of competition created by growth of heterotrophs receiving the additional COD. Overall, ozonation provided the expected benefits and had less negative impacts on processes in the alternating treatment, although after prolonged operation, benefits could become less significant. The alternating anoxic/aerobic reactor achieved twice the nitrification rates of its aerobic counterpart. Higher removal rates of estrogens were associated with higher nitrification rates, supporting the contention that the nitrifying biomass was responsible for their removal. The alternating treatment offered the better estrogen biodegradation. Microbial populations in both reactors were examined with fluorescent in situ hybridization. Dominance of rapid nitrifiers like Nitrosomonas and Nitrobacter (79.5%) in the alternating reactor, compared to a dominance of slower nitrifiers like Nitrosospira and Nitrospira (78.2%) in the aerobic reactor were found. The findings are important to design engineers, as reactors are typically designed based on nitrifiers’ growth rate determined in strictly aerobic conditions.

The aim of the investigation described in this work is to gain a better understanding of the processes involved in the oxidation of organic compounds by photolytic ozonation in a laboratory scale reactor. The results and discussions are presented in Chapter III. This chapter contains four parts. In the first part, mass transfer efficiency and the calculation of the mass transfer coefficient, KLa, as well as the ozone decomposition rate constant, KD, are presented and compared with those obtained by other investigators. The second part deals with the kinetics of the photolysis of 2,2',4,4',6,6'-hexachlorobiphenyl both in purified and natural lake water. Mathematical expressions and a discussion of the possible reaction processes involved are given. Kinetic models of ozonation and photolytic ozonation in purified and natural lake water are developed and discussed in part three. Rate constants are calculated from experimental data and used to predict values of substrate destruction with a mathematical model. The fourth part of this chapter deals with the identification of products from the photolysis, ozonation and photolytic ozonation of 2,2'4,4',6,6'-hexachlorobiphenyl. The products are isolated and identified using combined gas chromatography and mass spectroscopy, and reaction mechanisms are suggested.

Made available in DSpace on 2015-03-26T13:23:47Z (GMT). No. of bitstreams: 1 texto completo.pdf: 1765516 bytes, checksum: 4fbedf3e31cfced1feb83c5be1f48ef4 (MD5) Previous issue date: 2011-02-21 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Needing for treatment alternatives of wastewater from coffee fruits processing stimulates the study of alternative methods, in view to new techniques aimed at enabling the removal of these effluent pollutant load. One of the alternatives that need to be studied is the application of chemical treatment with ozone gas, considering the high oxidizing power of this compound. This study aimed to evaluate the effect of ozonation process on physical, chemical, and biochemical characteristics of wastewater from washing and peeling/pulping (ARC) coffee and to verify the pH influence on efficiency of wastewater ozonation in treatment. For the ozonation process, a gas-washing bottle was used with a capacity of one liter. Ozone gas was injected into the bottle through a porous plate with a flow rate of one liter/min-1. The influence of different combinations of pH (3.7, 7.0, and 10.0), ozone gas concentration (4.3, 8.6, and 12.8 mg L-1), and ozonation periods (0, 30, 60, 90, 120, 150, and 180 min.) was evaluated. Data were statistically analyzed by multiple linear regression. According to results, it was concluded that the treatment of wastewater from coffee fruits processing with ozone for analysis of Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), phenolic compounds, and apparent color does not appear to significantly affect the initial pH of the water in reducing their values during treatment. Thus, the removal of BOD, COD, and apparent color were higher with increasing ozone concentration, as the ozonation process occurred, resulting in maximum removal efficiencies of 11.0, 12.0, and 99.0%, respectively, for the concentration of 12.8 mg L-1 during 180 min. of ozonation. With regard to phenolic compounds, an increase in the removal percentage to ozone gas concentration of 8.6 mg L-1 was observed, with subsequent decrease in removal efficiency. The highest removal percentage of phenolic compounds was 68.0%, observed after ozonation and gas concentration of 8.6 mg L-1 for 180 min. Variables for total nitrogen, total suspended solids, and turbidity showed significant difference due to interaction between initial pH of wastewater and ozonation period. Concentration reduction of total nitrogen was more pronounced in the wastewater with lower pH, resulting in removal of 58.0% after 180 min. for pH equal to 3.7. With respect to total suspended solids variables and turbidity, a greater reduction was obtained during ozonation period, as they raised the initial pH of water. With respect to the total solids variables and total volatile solids, there was significant variation only due to the ozonation period, regardless of the gas concentration and initial pH of wastewater. Based on the results, it is possible to say that the use of ozone gas to treat wastewater from the coffee fruits processing is effective when compared to commonly used treatments for this effluent type, since it needs a short treatment period for more efficient removal of phenolic compounds, nitrogen, turbidity, and color. However, as most existing treatments, the treated wastewater with ozone gas alone did not respond to release some limits established by Brazilian legislation in force and further studies are needed to increase the process efficiency. / A necessidade de encontrar alternativas para o tratamento da água residuária proveniente do processamento dos frutos do cafeeiro estimula o estudo de métodos alternativos, visando a novas técnicas que possibilitem a remoção da carga poluidora desse efluente. Uma das alternativas que necessitam ser estudadas é o tratamento químico com aplicação de gás ozônio, haja vista o alto poder oxidante desse composto. Assim, objetivouse, com este estudo, avaliar o efeito do processo de ozonização nas características físicas, químicas e bioquímicas da água residuária resultante da lavagem e descascamento/despolpa do café (ARC) e verificar a influência do pH na eficiência da ozonização da água residuária em tratamento. Para o processo de ozonização, utilizou-se um frasco lavador de gás com capacidade de 1 L. O gás ozônio foi injetado no frasco, por meio de uma placa porosa, com uma vazão de 1 L min-1. Avaliou-se a influência de diferentes combinações de pH (3,7; 7,0 e 10,0), concentração do gás ozônio ( 4,3; 8,6 e 12,8 mg L-1) e períodos de ozonização (0, 30, 60, 90, 120, 150 e 180 min). Os dados foram submetidos à análise estatística por meio de regressão linear múltipla. De acordo com os resultados obtidos, foi possível concluir que o tratamento da água residuária do processamento dos frutos do cafeeiro com ozônio para as análises de DBO, DQO, compostos fenólicos e cor aparente não mostrou influência significativa do pH inicial da água na redução de seus valores durante o tratamento. Assim, as remoções de DBO, DQO e cor aparente foram maiores com o aumento da concentração de ozônio, à medida que ocorria o processo de ozonização, obtendo-se eficiências de remoção máximas de 11,0; 12,0 e 99,0%, respectivamente, para a concentração de 12,8 mg L-1 no período de ozonização de 180 min. Com relação aos compostos fenólicos, observou-se aumento no percentual de remoção até a concentração do gás ozônio de 8,6 mg L-1, com posterior decréscimo da eficiência de remoção. O maior percentual de remoção de compostos fenólicos foi de 68,0%, observado depois de 180 min. de ozonização e concentração do gás de 8,6 mg L-1. Para as variáveis nitrogênio total, sólidos suspensos totais e turbidez, verificou-se diferença significativa em decorrência da interação entre pH inicial da água residuária e período de ozonização. A redução da concentração de nitrogênio total foi mais acentuada na água residuária com menor pH, obtendo-se remoção de 58,0% depois de 180 min. para pH igual a 3,7. Com relação às variáveis sólidos totais, suspensos e turbidez, obteve-se maior redução durante o período de ozonização, à medida que se elevou o pH inicial da água. Com relação às variáveis sólidos totais e sólidos voláteis totais, ocorreu variação significativa somente em decorrência do período de ozonização, independentemente da concentração do gás e do pH inicial da água residuária. Com base nos resultados obtidos, é possível afirmar que o uso do gás ozônio no tratamento de águas residuárias provenientes do processamento dos frutos do cafeeiro é eficiente quando comparado aos tratamentos normalmente empregados para esse tipo de efluente, já que necessita de curto período de tratamento para obter eficientes remoções de compostos fenólicos, nitrogênio, turbidez e cor. Todavia, assim como a maioria dos tratamentos existentes, esta água residuária tratada com gás ozônio, isoladamente, não atendeu a alguns limites de lançamento estabelecidos pela legislação brasileira vigente, sendo necessários estudos posteriores para aumentar a eficiência do processo.

Orientador: Marcelo Cristianini / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-17T18:15:53Z (GMT). No. of bitstreams: 1 Amorim_EmanueleOliveiraCerqueira_M.pdf: 2851133 bytes, checksum: 521a3dc56b821671931089fc70f5b433 (MD5) Previous issue date: 2011 / Resumo: O ozonio e considerado um sanitizante seguro para uso em produtos alimenticios pela sua propriedade de auto-decomposicao em oxigenio, nao deixando residuos nos alimentos. O amido, por sua vez, e um produto de ampla aplicacao na industria de alimentos, especialmente pela sua propriedade de retencao de agua e capacidade de formar geis. Neste estudo, avaliou-se a eficiencia do ozonio como um metodo de descontaminacao do amido de mandioca e a influencia da umidade do produto na eficacia do tratamento. Alem disso, verificou-se o efeito do tratamento nas caracteristicas fisico-quimicas, sensoriais e nas propriedades de pasta do amido e, posteriormente, estudou-se o comportamento do produto tratado com ozonio, durante dois meses de estocagem. Em amido de mandioca com 18% de umidade, foram empregadas concentracoes de ozonio no ar de 40 e 113 ppm para avaliar a inativacao de E. coli, e uma concentracao de 118 ppm, para avaliacao da inativacao de esporos de B. subtilis. Os tempos de exposicao ao ozonio empregados foram de 30, 60, 90 e 120 minutos. O tratamento durante 120 minutos, nas duas concentracoes estudadas, promoveu uma reducao de aproximadamente 2 ciclos logaritmicos na populacao de E. coli inoculada no amido. Para os esporos de B. subtilis, por sua vez, os tratamentos nao resultaram em inativacao significativa (< 1 ciclo log). Em amido com 30% de umidade, foram estudadas as concentracoes de 40 e 118 ppm de ozonio para avaliar a inativacao de E. coli e esporos de B. subtilis. Na menor concentracao e maior tempo de exposicao empregados (40 ppm/120 minutos), foi obtida uma reducao de 3,6 ciclos logaritmicos na populacao de esporos de B. subtilis. E na concentracao de 118 ppm, aos 90 e 120 minutos de tratamento, foram obtidas reducoes superiores a 5 ciclos logaritmicos. Para a populacao de E. coli, por sua vez, os tratamentos a 40 ppm durante 60 minutos e 118 ppm por 30 minutos foram responsaveis pela obtencao de reducoes superiores a 6 ciclos logaritmicos na concentracao do microrganismo inoculado. Para avaliacao do efeito do ozonio nas caracteristicas fisico-quimicas (pH, cor e oxidacao), sensoriais (cor e odor) e nas propriedades de pasta do amido de mandioca, o produto com 30% de umidade foi submetido aos tratamentos com ozonio gasoso nas concentracoes de 40 e 118 ppm por 30, 60, 90 e 120 minutos para a menor, e por 30 e 60 minutos para a maior concentracao. O pH das amostras ozonizadas foi significativamente inferior (p<0,05) ao pH da amostra nao tratada. No entanto, a cor e o conteudo de carboxila e carbonila do amido de mandioca nao foram significativamente alterados pelo ozonio. Por sua vez, as propriedades de pasta do amido ozonizado foram parcialmente alteradas, sendo que o efeito do ozonio foi mais evidente nos parametros de pico de viscosidade e breakdown, proporcionando a obtencao de pastas de amido com maior poder de intumescimento e com menor estabilidade de pasta durante o cozimento sob agitacao. Na avaliacao sensorial, o efeito do ozonio foi mais evidente no atributo de odor do que no atributo de cor, sendo que metade das amostras ozonizadas sofreu o efeito do ozonio nas suas caracteristicas sensoriais. Para avaliacao das caracteristicas fisico-quimicas, sensoriais, microbiologicas e das propriedades de pasta do amido de mandioca tratado com ozonio, durante dois meses de estocagem, o produto com 30% de umidade foi submetido a 118 ppm de ozonio durante 90 minutos. Com excecao do pH, as caracteristicas fisicoquimicas (umidade, cor e oxidacao) do amido de mandioca nao foram significativamente alteradas pelo ozonio. Nas propriedades de pasta, o efeito do ozonio foi mais evidente nos parametros de pico de viscosidade, breakdown e setback, proporcionando a obtencao de pastas de amido com maior poder de intumescimento, menor estabilidade de pasta durante o cozimento sob agitacao e menor tendencia a retrogradacao. O tratamento com ozonio provocou alteracoes significativas nas caracteristicas sensoriais de cor e odor do amido, sendo seu efeito mais notavel no segundo atributo. Os resultados obtidos no estudo das caracteristicas do amido, ao longo do periodo de estocagem, indicaram uma maior estabilidade do produto quando o tratamento de ozonizacao foi empregado, evidenciada principalmente pelas variaveis fisico-quimicas. Quanto as caracteristicas microbiologicas, as amostras estudadas estavam de acordo com a legislacao vigente e a ozonizacao proporcionou a reducao da concentracao de B. cereus do produto. Alem disso, a carga microbiana das amostras permaneceu inalterada ao longo do periodo de estocagem / Abstract: Ozone is considered a safe sanitizer to use in foods, due to its property of self-decomposition into oxygen, leaving no residue in food. Starch, on the other hand, is widely used in food industries due to its high water-holding capacity and ability to form gels. In this study, the effectiveness of ozone as a method of decontamination of cassava starch and the influence of the moisture content of the product on ozone efficiency were studied. Furthermore, the effect of the ozone on the physicochemical and sensory characteristics and pasting properties of cassava starch was determined. Also, the behavior of the starch treated with ozone was studied during two months of storage. In starch with a final moisture content of approximately 18%, ozone concentrations of 40 and 113 ppm were employed to evaluate the inactivation of E. coli and a concentration of 118 ppm, to evaluate the inactivation of B. subtilis spores. The exposure times used were 30, 60, 90 and 120 minutes. The treatments of 120 minutes, in the concentrations of 40 and 113 ppm, promoted a decrease of about 2 logarithmic cycles on the population of E. coli. For the spores of B. subtilis, the treatments with ozone did not result in a significant inactivation (<1 decimal reduction). In starch with a final moisture content of approximately 30%, ozone concentrations of 40 and 118 ppm were employed to evaluate the inactivation of E. coli and B. subtilis spores. In the lower concentration and a higher exposure time employed (40 ppm/120 minutes), a reduction of 3.6 logarithmic cycles was obtained in the population of B. subtilis spores. At 118 ppm of ozone, for 90 and 120 minutes of treatment, the concentration of those microorganisms suffered decreases of above 5 logarithmic cycles. For the population of E. coli, on the other hand, the treatments at 40 ppm/60 minutes and 118 ppm/30 minutes were necessary to obtain decreases of above 6 logarithmic cycles in the concentration of the inoculated microorganism. In order to evaluate the effect of ozone on the physicochemical and sensory characteristics and pasting properties of cassava starch, the product with 30% of moisture was exposed to gaseous ozone at approximate concentrations of 40 ppm for 30, 60, 90 and 120 minutes and 118 ppm for 30 and 60 minutes. The pH of the ozonized samples was significantly lower (p<0.05) than the pH of the standard sample. However, the color and the carboxyl and carbonyl contents of the cassava starch were not altered significantly by ozone. On the other hand, the pasting properties of ozonized starch were partially altered and the effect of ozone was more evident on the peak viscosity and breakdown. The ozonized samples presented higher peak viscosities and lower cooking stability under agitation than the untreated and control samples. In the sensory evaluation, the effect of ozone on the odor attribute was more pronounced than on the color, with half of the ozonized samples having suffered the effect of ozone on the their sensory characteristics. To evaluate, during two months of storage, the physicochemical, sensory, rheological and microbiological characteristics of the cassava starch treated with ozone, the product with 30% of moisture was exposed to gaseous ozone at a concentration of 118 ppm for 90 minutes. Except for the pH, the physicochemical characteristics (moisture, color and oxidation) of cassava starch were not altered significantly by ozone. On the pasting properties, the effect of ozone was more evident on the peak viscosity, breakdown and setback. The ozonized samples presented higher peak viscosities, lower cooking stability under agitation and lower retrogradation than the untreated sample. The sensory characteristics of cassava starch were significantly altered by ozone and the odor was the most affected attribute. The results obtained indicated that, during the storage period, the ozonized sample was more stable than the untreated sample, especially as regards to physicochemical characteristics. For the microbiological characteristics, the samples studied were in accordance with current legislation and the ozonation treatment reduced the population of B. cereus in cassava starch. Furthermore, during the storage period, the microbial load of the samples remained unchanged / Mestrado / Mestre em Tecnologia de Alimentos