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Disinfection of municipal wastewater with ozone for agriultural use / Desinfecção de efluentes de ETE com ozonio para uso agricola
Doralice Meloni Assirati
DATA DE PUBLICAÇÃO
Disinfection of wastewater, prior to its use in agriculture, is a treatment process indispensable to the protection of public health. In this context, ozone constitutes an alternative disinfectant to chlorine since it is very effective against a wide variety of pathogenic organisms and minimizes the formation of trihalomethanes. In this hesis, the effectiveness of ozone against bacteria, protozoa and helminths was evaluated as well as the interference of the quality of the wastewater in the disinfection process. Effluents from an anaerobic pond and from an anaerobic pond plus an aerobic sand filter from a sewage treatment facility located in the city of Limeira in the state of São Paulo were disinfected in a plug flow pilot reactor. Ozone doses from 8 to 21 mg L-1 were needed to disinfect the anaerobic pond effluent to meet standards set by the World Health Organization for agricultural use. The sand filter effluents, aerobic and more stabilized, required up to 4 mg L-1. Colored compounds present in the anaerobic pond effluent consumed ozone more or less prior to the beginning of the inactivation of coliforms. An exponential correlation was found between the consumption of ozone and the true color of the effluents with correlation indexes higher than 90%. Contact time was found not to be a factor affecting the disinfection efficiency of ozone against total coliforms and E. coli since the mass transfer conditions were met. The results concerning the inactivation of protozoa and helminths were found to be inconclusive due to the inadequacy of the analytical methods employed. Regardless of the color, the characteristics of the effluents were not altered significantly by the doses of ozone used during the experiments, up to 34 mg L-1 for the anaerobic pond effluents and up to 21 mg L-1 for the sand filter effluents