Compostagem de lodo de esgoto e indicadores de patogenicidade
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Data
2018-11-12
Autores
Faria, Marianne Fidalgo de [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
No Brasil, a maior parte do lodo de esgoto sanitário gerado nas Estações de Tratamento de Esgoto é destinada a aterros sanitários, o que preocupa técnicos e autoridades, que buscam alternativas de destinação mais adequadas ao meio ambiente. O processo de compostagem permite a estabilização e a higienização do lodo de esgoto, que pode então ser aplicado em solos agrícolas, aproveitando a matéria orgânica e os nutrientes ali presentes. O objetivo principal deste trabalho foi estudar de forma detalhada o comportamento dos indicadores de patogenicidade Salmonella spp., coliformes termotolerantes e ovos viáveis de Ascaris spp. em função da temperatura e da umidade durante o processo de compostagem de lodo de esgoto com diferentes materiais estruturantes, verificando se o processo é eficaz na higienização do material. Para isto, o estudo foi dividido em quatro experimentos. No Experimento 1, sensores de temperatura foram instalados em três diferentes perfis da pilha de compostagem (topo, meio e base) e verificou-se que a mistura de lodo de esgoto com bagaço de cana-de-açúcar apresentou temperaturas mais uniformes nos três perfis, a mistura com casca de eucalipto apresentou as temperaturas mais elevadas no topo e no meio da pilha e a mistura com casca de arroz apresentou baixas temperaturas em todos os perfis, sendo, então, considerada uma mistura inadequada para compostagem. O Experimento 2 avaliou dois métodos para determinação do número de ovos viáveis de Ascaris spp. em amostras de lodo de esgoto, o método da USEPA e o da Norma Mexicana, sendo o método da USEPA considerado o mais eficiente na separação dos ovos viáveis de Ascaris spp. nas amostras de lodo de esgoto analisadas. O Experimento 3 avaliou ao longo do processo de compostagem a presença de Salmonella spp. e o decaimento de coliformes termotolerantes e ovos viáveis de Ascaris spp. A presença de Salmonella spp. foi verificada em apenas uma ocorrência para cada mistura estudada, na faixa de temperatura entre 35ºC e 55ºC, não sendo observada ao final do processo de compostagem. Os coliformes termotolerantes apresentaram queda em sua população seguida de aumento, porém ao final da compostagem os valores observados estavam dentro dos limites estabelecidos pela legislação. Para ovos viáveis de Ascaris spp. foi estimado um tempo de persistência de 25 dias na mistura de lodo de esgoto com bagaço de cana-de-açúcar e de 54 dias na mistura de lodo de esgoto com casca de eucalipto. O Experimento 4 avaliou o decaimento de coliformes termotolerantes em amostras de lodo de esgoto submetidas a temperatura constante (42ºC) de acordo com o decaimento da umidade e atividade de água. Foi possível verificar correlações significativas entre as variáveis, mas a curva de decaimento de umidade não foi acompanhada pela curva de decaimento de atividade de água, indicando que, em alguns casos, os valores de umidade podem ser considerados inadequados para o desenvolvimento de microrganismos, visto que os valores de atividade de água podem ainda estar adequados, permitindo o desenvolvimento microbiológico em temperaturas adequadas. Por fim, pode-se concluir que nos processos de compostagem de lodo de esgoto com casca de eucalipto e com bagaço de cana-de-açúcar foram observadas temperaturas adequadas para a higienização do material, comprovada pelos resultados das análises microbiológicas realizadas, estando o produto final de compostagem, assim, seguro para aplicação no campo em culturas permitidas pela legislação pertinente.
In Brazil, most of the biosolids generated daily by Wastewater Treatment Plants are destined to landfills, which raises a great concern of technicians and authorities, who seek alternatives of destination more appropriate to the environment. The composting allows the stabilization of biosolids, reducing or even eliminating the load of pathogenicity indicators present in it, which can then be applied to agricultural soils, taking advantage of its organic matter and nutrients. The main objective of this work was to study in detail the behavior of the pathogenicity indicators Salmonella spp., thermotolerant coliforms and Ascaris spp. viable ova as a function of temperature and moisture during the biosolids composting with different structuring materials, verifying if the process is effective in sanitizing the material. Therefore, the study was divided into four experiments. In Experiment 1, temperature sensors were installed in three different profiles of the compost pile (top, middle and bottom) and it was verified that the mixture of biosolids with sugarcane bagasse presented more uniform temperatures in the three profiles, the mixture with Eucalyptus bark showed the highest temperatures at the top and middle of the pile and the mixture with rice husk showed low temperatures in all the profiles, being considered an inadequate mixture for composting. Experiment 2 evaluated two methods for determining the number of viable ova of Ascaris spp. in biosolids samples, the USEPA method and the Norma Mexicana method, and the USEPA method was considered the most efficient in determining the number of viable ova of Ascaris spp. in the biosolids samples analyzed. Experiment 3 evaluated throughout the composting process the presence of Salmonella spp. and the decay of thermotolerant coliforms and viable ova of Ascaris spp. The presence of Salmonella spp. was verified in only one occurrence for each mixture studied, in the temperature range between 35ºC and 55ºC, not being observed at the end of the composting process. The thermotolerant coliforms presented a decrease in their population followed by an increase, but at the end of the composting their values were within the limits established by the legislation. For viable ova of Ascaris spp. a persistence time of 25 days was estimated in the mixture of biosolids with sugarcane bagasse and of 54 days in the mixture of biosolids with eucalyptus bark. The Experiment 4 evaluated the decay of thermotolerant coliforms submitted to constant temperature (42ºC) according to the fall of moisture and water activity. It was possible to verify significant correlations between the variables, but the moisture decay curve was not accompanied by the water activity decay curve, indicating that, in some cases, moisture values may be considered inadequate for the development of microorganisms, however the values of water activity may still be adequate, allowing microbiological development at suitable temperatures. Finally, it can be concluded that during composting of biosolids with eucalyptus bark and biosolids with sugarcane bagasse, adequate temperatures were observed for the sanitation of the material, as evidenced by the results of the microbiological analyzes, being thus the final product safe for land application in crops allowed by the legislation.
In Brazil, most of the biosolids generated daily by Wastewater Treatment Plants are destined to landfills, which raises a great concern of technicians and authorities, who seek alternatives of destination more appropriate to the environment. The composting allows the stabilization of biosolids, reducing or even eliminating the load of pathogenicity indicators present in it, which can then be applied to agricultural soils, taking advantage of its organic matter and nutrients. The main objective of this work was to study in detail the behavior of the pathogenicity indicators Salmonella spp., thermotolerant coliforms and Ascaris spp. viable ova as a function of temperature and moisture during the biosolids composting with different structuring materials, verifying if the process is effective in sanitizing the material. Therefore, the study was divided into four experiments. In Experiment 1, temperature sensors were installed in three different profiles of the compost pile (top, middle and bottom) and it was verified that the mixture of biosolids with sugarcane bagasse presented more uniform temperatures in the three profiles, the mixture with Eucalyptus bark showed the highest temperatures at the top and middle of the pile and the mixture with rice husk showed low temperatures in all the profiles, being considered an inadequate mixture for composting. Experiment 2 evaluated two methods for determining the number of viable ova of Ascaris spp. in biosolids samples, the USEPA method and the Norma Mexicana method, and the USEPA method was considered the most efficient in determining the number of viable ova of Ascaris spp. in the biosolids samples analyzed. Experiment 3 evaluated throughout the composting process the presence of Salmonella spp. and the decay of thermotolerant coliforms and viable ova of Ascaris spp. The presence of Salmonella spp. was verified in only one occurrence for each mixture studied, in the temperature range between 35ºC and 55ºC, not being observed at the end of the composting process. The thermotolerant coliforms presented a decrease in their population followed by an increase, but at the end of the composting their values were within the limits established by the legislation. For viable ova of Ascaris spp. a persistence time of 25 days was estimated in the mixture of biosolids with sugarcane bagasse and of 54 days in the mixture of biosolids with eucalyptus bark. The Experiment 4 evaluated the decay of thermotolerant coliforms submitted to constant temperature (42ºC) according to the fall of moisture and water activity. It was possible to verify significant correlations between the variables, but the moisture decay curve was not accompanied by the water activity decay curve, indicating that, in some cases, moisture values may be considered inadequate for the development of microorganisms, however the values of water activity may still be adequate, allowing microbiological development at suitable temperatures. Finally, it can be concluded that during composting of biosolids with eucalyptus bark and biosolids with sugarcane bagasse, adequate temperatures were observed for the sanitation of the material, as evidenced by the results of the microbiological analyzes, being thus the final product safe for land application in crops allowed by the legislation.
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Palavras-chave
biossólidos, composto orgânico, higienização, coliformes termotolerantes, Salmonella spp., ovos viáveis de Ascaris spp., biosolids, organic compost, sanitation, thermotolerant coliforms, Salmonella spp., viable ova of Ascaris spp.