Tratamento e valorização de efluentes líquidos da indústria do azeite através do cultivo de microalgas
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2021-03-31
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As atividades antropogénicas são as principais responsáveis pela contaminação dos recursos hídricos, sendo que a crescente preocupação relativa à quantidade e qualidade da água de consumo, aliada à inquietação pela sustentabilidade dos ecossistemas, conduziu à necessidade de regulamentar a descarga de efluentes para o meio ambiente. A indústria de extração de azeite é uma atividade económica particularmente relevante nos países mediterrânicos, com uma elevada geração de águas residuais normalmente denominadas de águas ruças. Estas águas caracterizam-se por uma elevada carga orgânica, reduzida biodegradabilidade e elevado carácter fitotóxico, necessitando de processos de tratamento eficientes. As limitações técnicas e económicas têm inviabilizado um método de tratamento globalmente aceite para este efluente líquido, mas a biorremediação através de microalgas apresenta-se como vantajosa, por ser um processo ecológico, sem poluição secundária, eficaz na remoção de substâncias e que permite a reutilização da biomassa produzida. O objetivo principal deste trabalho foi avaliar o potencial de biorremediação de efluentes líquidos da indústria do azeite, pelas espécies de microalgas verdes, Chlorella vulgaris (Cv) Chlorella protothecoides (Cp) e Scnedesmus obliquus (So) e pela cianobactéria Arthrospira maxima (Am). Durante este estudo foi avaliada a capacidade das microalgas removerem a carga poluente de águas de lavagem de azeitona e águas ruças, através da remoção de Carência Química de Oxigénio (CQO), polifenóis, fósforo e nitratos. A produção de biomassa microalgal foi monitorizada para ambas as águas residuais em estudo, através do peso seco e da taxa de produtividade máxima das microalgas, no final de cada tratamento. Pela complexidade dos efluentes, percebeu-se a importância do fator diluição, partindo da base de 5% para a água ruça (AR) e 50% para a água de lavagem (AL). Para ambos os efluentes, os inóculos da Chlorella protothecoides (Cp) foram os que melhor responderam, com pesos máximos (X) de 783,3 mg/L e produtividade máxima (PXmax) de 165,8 mg/L/dia para a água ruça (AR) e X = 691,6 mg/L, PXmax = 107,9 mg/L/dia para a água de lavagem (AL). As percentagens de remoção de CQO oscilaram entre os 41,8% e os 61,6% no caso da água ruça e entre os 36,2% e os 67,9%, nas culturas com água de lavagem, sendo as espécies Scenedesmus obliquus (So) e as Chlorellas (Cv e Cp) as que apresentaram os menores e os maiores resultados, respetivamente. Devido à elevada dificuldade de degradação biológica, as percentagens máximas de remoção dos polifenóis não vão além dos 40,3% na água ruça e dos 48,1% na água de lavagem. A microalga Arthrospira maxima (Am) obteve o melhor desempenho na AR, enquanto que na AL se destacou a espécie Chlorella protothecoides (Cp). Valores significativos de remoção, do macronutriente fósforo (P-PO4) foram apenas verificados com a Arthrospira maxima (Am), 67,0% para a água ruça e 36,0%, para a água de lavagem de azeitona. Relativamente aos nitratos (N-NO3), foram obtidas taxas de remoção muito satisfatórias, com todas as microalgas. Com uma taxa de remoção de aproximadamente 84,0%, destacaramse a Arthrospira maxima (Am) na água de lavagem e a Scenedesmus obliquus (So) na água ruça. Apesar de serem mais favoráveis os resultados obtidos para o uso das microalgas no tratamento da água ruça, a continuação dos estudos não será exequível, se este efluente não for sujeito a um tratamento primário que possibilite a remoção da elevada toxicidade deste efluente, que induz a morte celular das microalgas ao fim de 4 dias. Para a água de lavagem de azeitona, embora sejam menos promissores os resultados obtidos, será possível a utilização das espécies Chlorella vulgaris (Cv) e Chlorella protothecoides (Cp), no processo de tratamento desta água residual, desde que sejam ajustadas as condições ótimas de crescimento das microalgas.
Anthropogenic activities are largely responsible for water resources contamination. Growing concern regarding the quantity and quality of drinking water, coupled with ecosystems sustainability, has led to the need for regulate the discharge of effluents into the environment. The olive oil extraction industry is a particularly relevant economic activity in Mediterranean countries, with a high generation of waste water, commonly referred to olive mil wastewater. These waters are characterized by a high organic load, reduced biodegradability and a high phytotoxic character, requiring efficient treatment processes. Technical and economic limitations have hindered a globally accepted treatment method for this type of effluent. Bioremediation through microalgae is useful, because is an environmentally friendly process with no secondary pollution, effective in removing substances and allowing the reuse of biomass produced. The main objective of this work was to evaluate the potential for bioremediation of effluents from the olive oil industry, by the species of green microalgae, Chlorella vulgaris (Cv) Chlorella protothecoides (Cp) and Scnedesmus obliquus (So) and by the cyanobacterium Arthrospira maxima (Am). During this study, the ability of microalgae to remove the polluting load from olive washing and redwater waters was evaluated, by removing Chemical Oxygen Demand (COD), polyphenols, phosphorus and nitrates. The production of microalgal biomass was monitored for both wastewaters under study, through the dry weight and the maximum productivity rate of the microalgae, at the end of each treatment. Due to the complexity of the effluents, we perceive the importance of the dilution factor, starting from the base of 5% for olive mill wastewater (OMW) and 50% for olives washing wastewater (OWW). For both effluents, Chlorella protothecoides (Cp) inocula responded best, with maximum weights (X) of 783.3 mg / L and maximum productivity (PXmax) of 165.8 mg / L / day for olive mill wastewater and X = 691.6 mg / L, PXmax = 107.9 mg / L / day for olives washing wastewater. The percentages of chemical oxygen demand removal (COD) ranged from 41.8% to 61.6% in the case of olive mill wastewater and between 36.2% and 67.9% in cultures with washing water, with Scenedesmus obliquus species (So) and Chlorellas (Cv and Cp), which presented the worst and best results, respectively. Due to difficult biological degradation, the maximum percentages for the removal of polyphenols did not exceed 40.3% in olive mill wastewater (OMW) and 48.1% in olive mill wastewater. The microalgae Arthrospira maxima (Am) had the best performance in OMW, while in OWW the species Chlorella protothecoides (Cp) stood out. Significant removal values of macronutrient phosphorus (P-PO4) were only verified with Arthrospira maxima (Am), 67.0% for olive mill wastewater and 36.0% for washing water. Regarding nitrates (N-NO3), very satisfactory removal rates were obtained with all microalgae. With a removal rate of aproximately 84.0%, Arthrospira maxima (Am) stood out in the washing water and Scenedesmus obliquus (So) in olive mill wastewater. Although the results obtained for the use of microalgae in the treatment of olive mill wastewater seem more favourable, further studies will not be feasible if this effluent is not subjected to a more complex primary treatment, since the excessive amount of its load toxicity induces bioremediators death after 4 days. For olive mill wastewater, although the immediate results are less promising, it is possible to use the species Chlorella vulgaris (Cv) and Chlorella protothecoides (Cp), in the process of treating this residual waste water, provided that the optimal growth conditions for the microalgae are met.
Anthropogenic activities are largely responsible for water resources contamination. Growing concern regarding the quantity and quality of drinking water, coupled with ecosystems sustainability, has led to the need for regulate the discharge of effluents into the environment. The olive oil extraction industry is a particularly relevant economic activity in Mediterranean countries, with a high generation of waste water, commonly referred to olive mil wastewater. These waters are characterized by a high organic load, reduced biodegradability and a high phytotoxic character, requiring efficient treatment processes. Technical and economic limitations have hindered a globally accepted treatment method for this type of effluent. Bioremediation through microalgae is useful, because is an environmentally friendly process with no secondary pollution, effective in removing substances and allowing the reuse of biomass produced. The main objective of this work was to evaluate the potential for bioremediation of effluents from the olive oil industry, by the species of green microalgae, Chlorella vulgaris (Cv) Chlorella protothecoides (Cp) and Scnedesmus obliquus (So) and by the cyanobacterium Arthrospira maxima (Am). During this study, the ability of microalgae to remove the polluting load from olive washing and redwater waters was evaluated, by removing Chemical Oxygen Demand (COD), polyphenols, phosphorus and nitrates. The production of microalgal biomass was monitored for both wastewaters under study, through the dry weight and the maximum productivity rate of the microalgae, at the end of each treatment. Due to the complexity of the effluents, we perceive the importance of the dilution factor, starting from the base of 5% for olive mill wastewater (OMW) and 50% for olives washing wastewater (OWW). For both effluents, Chlorella protothecoides (Cp) inocula responded best, with maximum weights (X) of 783.3 mg / L and maximum productivity (PXmax) of 165.8 mg / L / day for olive mill wastewater and X = 691.6 mg / L, PXmax = 107.9 mg / L / day for olives washing wastewater. The percentages of chemical oxygen demand removal (COD) ranged from 41.8% to 61.6% in the case of olive mill wastewater and between 36.2% and 67.9% in cultures with washing water, with Scenedesmus obliquus species (So) and Chlorellas (Cv and Cp), which presented the worst and best results, respectively. Due to difficult biological degradation, the maximum percentages for the removal of polyphenols did not exceed 40.3% in olive mill wastewater (OMW) and 48.1% in olive mill wastewater. The microalgae Arthrospira maxima (Am) had the best performance in OMW, while in OWW the species Chlorella protothecoides (Cp) stood out. Significant removal values of macronutrient phosphorus (P-PO4) were only verified with Arthrospira maxima (Am), 67.0% for olive mill wastewater and 36.0% for washing water. Regarding nitrates (N-NO3), very satisfactory removal rates were obtained with all microalgae. With a removal rate of aproximately 84.0%, Arthrospira maxima (Am) stood out in the washing water and Scenedesmus obliquus (So) in olive mill wastewater. Although the results obtained for the use of microalgae in the treatment of olive mill wastewater seem more favourable, further studies will not be feasible if this effluent is not subjected to a more complex primary treatment, since the excessive amount of its load toxicity induces bioremediators death after 4 days. For olive mill wastewater, although the immediate results are less promising, it is possible to use the species Chlorella vulgaris (Cv) and Chlorella protothecoides (Cp), in the process of treating this residual waste water, provided that the optimal growth conditions for the microalgae are met.
Descrição
Dissertação apresentada à Escola de Ciências da Vida e do Ambiente da Universidade de Trás-os-Montes e Alto Douro, como parte dos requisitos para a obtenção do grau de Mestre em Engenharia do Ambiente
Palavras-chave
Microalgas , biorremediação