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Advisor(s)
Abstract(s)
O estágio curricular desenvolvido como requisito parcial para a obtenção de grau de mestre
foi realizado na SIMDOURO – Estação de Tratamento de Águas Residuais (ETAR) de Paço de
Sousa. O tema desenvolvido foi o estudo da otimização da digestão anaeróbia na referida ETAR.
Os ensaios tiveram como objetivo estudar a influência de diversos fatores na produção de biogás:
diferentes pré-tratamentos enzimáticos (simples e combinados) e térmicos nas lamas mistas;
temperatura do processo; codigestão de lamas mistas com microalgas e com efluente rico em óleos
e gorduras provenientes de uma indústria de produção de biodiesel. Foram realizados testes em
sistema fechado para avaliação do potencial de produção de metano, BMP (biochemical methane
potential) com uma duração aproximada de 14 dias.
O pré-tratamento enzimático com apenas uma enzima causou uma redução na produção de
biogás, sugerindo uma possível inibição do processo de digestão anaeróbia. A produção de biogás
na amostra pré-tratada enzimática e termicamente foi maior do que na amostra submetida apenas
ao pré-tratamento enzimático. Quanto ao grupo de ensaios com enzimas combinadas, o uso
simultâneo de 3 grupos de enzimas (proteases, lípases e celulases) deu origem a maior produção
de biogás, correspondente a 0,128 Nml/mg sólidos voláteis iniciais (SVi). O uso de enzimas
celulolíticas originou menor produção específica, sendo esta de 0,121 Nml/mg SVi. Verificou-se
que a codigestão de lamas mistas com até 4,5 % de microalga Chlorella vulgaris não teve efeito
inibidor. Para as temperaturas testadas (43 e 48 ºC), a maior produção de biogás deu-se a 43 ºC. A
codigestão com 0,94%v/v de um efluente rico em óleos e gorduras resultou na produção de um
volume adicional de biogás de 18,4%.
O estudo desenvolvido levou ainda a perceber que 24% do biogás produzido pela ETAR é
desperdiçado devido à baixa potência elétrica do cogerador (170 kW). Verificou-se que o uso de
um cogerador com uma maior potência (226 kW) eliminaria essas perdas, produzindo energia
elétrica equivalente a 1 976 764 kWh anual e gerando assim uma receita bruta correspondente a
151% das vendas atuais, que após a liquidação da fatura de energia injetada na rede resultaria num
saldo extra de +28 325 € anuais
The internship developed as a partial requirement for obtaining a master's degree was carried out at SIMDOURO – Wastewater Treatment Plant (WWTP) in Paço de Sousa. The theme developed was the study of the optimization of anaerobic digestion in the above mentioned WWTP. The tests aimed to study the influence of several factors on biogas production: different enzymatic (single and combined) and thermal pre-treatments of mixed sludge; process temperature; the co-digestion of mixed sludge with microalgae and with effluent rich in oils and fats from a biodiesel production industry. Tests were carried out in a closed system to evaluate the biochemical methane potential (BMP), with an approximate duration of 14 days. Enzymatic pre-treatment with only one enzyme caused a reduction in biogas production, suggesting a possible inhibition of the anaerobic digestion process. The production of biogas in the enzymatically and thermally pre-treated sample was higher than in a sample submitted only to enzymatic pre-treatment. As for the combined enzyme assay group, the simultaneous use of the 3 enzyme groups (proteases, lipases and cellulases) resulted in a higher biogas production, corresponding to 0.128 Nml/mg initial volatile solids (SVi). The use of 8 cellulolytic enzymes resulted in lower specific production, which was 0.121 Nml/mg SVi. It was found that 4.5% of microalgae Chlorella vulgaris has no inhibitory effect when co-digested with mixed sludge. For the temperatures tested (43 and 48 ºC), the highest production of biogas occurred at 43 ºC. The co digestion with effluent rich in oils and fats (0.94%v/v) resulted in the production of an additional volume of biogas of 18%. The study developed also confirmed that 24% of the biogas produced by the WWTP is wasted due to the low electrical power of the co-generator (170 kW). The use of a co-generator with a higher power (226 kW) would eliminate these losses, producing annually electricity equivalent to 1,976,764 kWh and generating a gross revenue corresponding to 151% of current sales, which after the billing of energy injected in the grid would result in an extra balance of €28,325 per year
The internship developed as a partial requirement for obtaining a master's degree was carried out at SIMDOURO – Wastewater Treatment Plant (WWTP) in Paço de Sousa. The theme developed was the study of the optimization of anaerobic digestion in the above mentioned WWTP. The tests aimed to study the influence of several factors on biogas production: different enzymatic (single and combined) and thermal pre-treatments of mixed sludge; process temperature; the co-digestion of mixed sludge with microalgae and with effluent rich in oils and fats from a biodiesel production industry. Tests were carried out in a closed system to evaluate the biochemical methane potential (BMP), with an approximate duration of 14 days. Enzymatic pre-treatment with only one enzyme caused a reduction in biogas production, suggesting a possible inhibition of the anaerobic digestion process. The production of biogas in the enzymatically and thermally pre-treated sample was higher than in a sample submitted only to enzymatic pre-treatment. As for the combined enzyme assay group, the simultaneous use of the 3 enzyme groups (proteases, lipases and cellulases) resulted in a higher biogas production, corresponding to 0.128 Nml/mg initial volatile solids (SVi). The use of 8 cellulolytic enzymes resulted in lower specific production, which was 0.121 Nml/mg SVi. It was found that 4.5% of microalgae Chlorella vulgaris has no inhibitory effect when co-digested with mixed sludge. For the temperatures tested (43 and 48 ºC), the highest production of biogas occurred at 43 ºC. The co digestion with effluent rich in oils and fats (0.94%v/v) resulted in the production of an additional volume of biogas of 18%. The study developed also confirmed that 24% of the biogas produced by the WWTP is wasted due to the low electrical power of the co-generator (170 kW). The use of a co-generator with a higher power (226 kW) would eliminate these losses, producing annually electricity equivalent to 1,976,764 kWh and generating a gross revenue corresponding to 151% of current sales, which after the billing of energy injected in the grid would result in an extra balance of €28,325 per year
Description
Keywords
Codigestão Efluente rico em óleos e gorduras Microalgas Pré-tratamento enzimático Pré-tratamento térmico Temperatura Biogás Lamas Codigestion Effluent rich in oils and fats Enzymatic pretreatment Heat pretreatment Microalgae Temperature Biogas Sludge