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A produção de azeite é uma actividade importante no tecido económico de Portugal, existindo inúmeros lagares de azeite de pequena e média dimensão que utilizam, como tecnologias de processamento da azeitona, o método tradicional de prensagem e o método de centrifugação em contínuo, de três fases. Estes métodos têm como resíduo final um efluente fortemente corado, com uma elevada carência química de oxigénio (CQO) tipicamente acima de 100 g L-1, com elevado teor em fenóis e poli-fenóis, também conhecido como águas ruças. Até recentemente, as águas ruças eram eliminadas por descarga em cursos de água, originando graves problemas ambientais nas províncias de concentração dos lagares de azeite (Trás-os-Montes, Beira Interior e Alentejo), agravados pelo carácter sazonal da actividade olivícola.
A maior parte dos estudos efectuados sobre o tratamento de efluentes de lagares de azeite utilizam processos oxidativos. Neste contexto, o principal objectivo deste trabalho consistiu em avaliar o comportamento de diferentes processos oxidativos no tratamento deste tipo de efluentes. Para tal, realizaram-se dois tipos de estudos distintos: aplicação de processos oxidativos em separado e em série. Os processos oxidativos escolhidos foram a ozonização e a oxidação anódica, com um eléctrodo de BDD. Para eliminar inicialmente parte da carga orgânica, recorreu-se à electrocoagulação com ânodos consumíveis de ferro.
Em relação aos processos em separado, usando o efluente a pH natural, com a aplicação de ozonização conseguiram-se obter remoções de 31% de CQO e 52% de fenóis ao fim de noventa minutos de ensaio; o recurso à oxidação anódica permitiu a obtenção de resultados mais satisfatórios, tendo-se obtido remoções de 71% de CQO, 67% do teor de fenóis e 67% de DOC ao fim de oito horas de ensaio.
Após a optimização das condições de electrocoagulação, efectuaram-se tratamentos combinados, que permitiram obter melhores resultados. Esta combinação de processos permitiu obter remoções de CQO de 80%, de 67% de DOC e 89% de fenóis aquando da aplicação de uma electrocoagulação seguida de oxidação anódica; com a aplicação de uma electrocoagulação seguida de ozonização obtiveram-se remoções de 66% de CQO, 59% de fenóis e 40% de DOC.
Deste modo, pode concluir-se que a aplicação de processos oxidativos combinados é a técnica mais vantajosa para o tratamento de efluentes provenientes de lagares de azeite.
Olive oil production is an important activity in the Portuguese economy. There are many olive mills, either with large or small dimensions, which use the traditional technique of pressing and the continuous three stage centrifugation as the main technologies for processing the olives. These methods have strongly colored wastewater as a final residue, which has high levels of chemical oxygen demand (COD), commonly above 100 g L-1 , as well as high phenols and poli-phenols concentration. Until recently, the olive oil production wastewaters were discharged into natural watercourses, originating serious environmental damage near the areas where olive mills are more common (Trás-os-Montes, Beira Interior e Alentejo), which is aggravated by the seasonal olive growing nature. The most investigated treatment solutions for the olive oil wastewaters take in account oxidation processes. This is the main point on which this dissertation is going to focus, and the main objective is to investigate the best oxidating treatment for this kind of wastewater. To pursue this objective, two different types of experiments were tested: separated application of the oxidation processes and a combined method of those processes. As oxidative processes ozonation and anodic oxidation were chosen. To improve this study, it was decided to submit the effluent to an electrocoagutation, prior to the application of the oxidative techniques. Concerning the separate application, COD removals of 31% and phenols removal of 52% were obtained in 90 minutes with ozonation; the anodic oxidation application had the most satisfactory results, as the COD has been removed by 71%, the phenols concentration and DOC have been removed by 67% have been achieved in eight hours. Both the experiments took place at effluent natural pH. The combined method has permitted to obtain most effective results, and thus they turned out to be a very attractive option when it comes to solve the environmental damage that the olive oil production wastewaters represent. The combined method have allowed COD, TOC and phenols removals of 80%, 67% and 89%, respectively, when electrocoagulation followed by anodic oxidation was applied; when the wastewater was submitted to electrocoagulation followed by ozonation, the COD removals chanced to over 66%, the phenols removal to 59% and the TOC removal to 40%. Thus, these results lead to the conclusion that the application of combined methods is the most advantageous technique for the treatment of olive oil production wastewaters.
Olive oil production is an important activity in the Portuguese economy. There are many olive mills, either with large or small dimensions, which use the traditional technique of pressing and the continuous three stage centrifugation as the main technologies for processing the olives. These methods have strongly colored wastewater as a final residue, which has high levels of chemical oxygen demand (COD), commonly above 100 g L-1 , as well as high phenols and poli-phenols concentration. Until recently, the olive oil production wastewaters were discharged into natural watercourses, originating serious environmental damage near the areas where olive mills are more common (Trás-os-Montes, Beira Interior e Alentejo), which is aggravated by the seasonal olive growing nature. The most investigated treatment solutions for the olive oil wastewaters take in account oxidation processes. This is the main point on which this dissertation is going to focus, and the main objective is to investigate the best oxidating treatment for this kind of wastewater. To pursue this objective, two different types of experiments were tested: separated application of the oxidation processes and a combined method of those processes. As oxidative processes ozonation and anodic oxidation were chosen. To improve this study, it was decided to submit the effluent to an electrocoagutation, prior to the application of the oxidative techniques. Concerning the separate application, COD removals of 31% and phenols removal of 52% were obtained in 90 minutes with ozonation; the anodic oxidation application had the most satisfactory results, as the COD has been removed by 71%, the phenols concentration and DOC have been removed by 67% have been achieved in eight hours. Both the experiments took place at effluent natural pH. The combined method has permitted to obtain most effective results, and thus they turned out to be a very attractive option when it comes to solve the environmental damage that the olive oil production wastewaters represent. The combined method have allowed COD, TOC and phenols removals of 80%, 67% and 89%, respectively, when electrocoagulation followed by anodic oxidation was applied; when the wastewater was submitted to electrocoagulation followed by ozonation, the COD removals chanced to over 66%, the phenols removal to 59% and the TOC removal to 40%. Thus, these results lead to the conclusion that the application of combined methods is the most advantageous technique for the treatment of olive oil production wastewaters.
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Oxidação anódica Biodegradabilidade aeróbia Lagares de azeite - Efluentes Electrocuagulação