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Abstract(s)
Os resíduos sólidos, tais como lamas provenientes de uma estação de tratamento de águas residuais (ETAR), resíduos de óleos e gorduras animais, e outros resíduos industriais, são de especial interesse, uma vez que podem ser usados como fontes para a produção de energia renovável. O processo de digestão anaeróbia (DA) permite converter este tipo de resíduos/biomassa em biogás, que pode ser utilizado para a produção de energia elétrica e térmica, sendo, no entanto, um processo complexo e dependente das propriedades da biomassa, assim como das condições aplicadas ao reator. Neste contexto, o presente estudo foi realizado no âmbito da unidade curricular “Dissertação/Projeto/Estágio” do Mestrado em Energias Sustentáveis, numa ETAR pertencente ao grupo SIMDOURO – Saneamento do Grande Porto, S.A.. O estágio teve como principal objetivo replicar à escala laboratorial o digestor anaeróbio existente na ETAR, e analisar a influência da incorporação de um resíduo sólido industrial rico em óleos e gorduras na quantidade de biogás produzido durante o processo de digestão anaeróbia a partir de lamas da ETAR. O resíduo incorporado é proveniente de uma empresa de valorização de gorduras e afins, para a produção de biodiesel. Para este estudo procedeu-se à realização de diferentes ensaios em paralelo, em que as proporções de lamas de ETAR (neste caso uma mistura de lama primária e lama secundária) foram mantidas iguais às que se verificavam no digestor real, respetivamente 60% e 40%, variando a proporção de resíduo adicionado à mistura entre 1% e 7%, e tendo-se fixado a percentagem de inóculo, neste caso lama do digestor, em 50%. Durante este estudo foi medido o volume de biogás produzido, ao longo do período de duração do ensaio que era de cerca de 15 dias, ou até a produção de biogás cessar. Procedeu-se também à caraterização físico-química das lamas, do resíduo sólido industrial (co-substrato) e da mistura presente em cada reator, tendo sido determinados osseguintes parâmetros, antes e depois de cada ensaio: pH, temperatura,sólidos totais, sólidos voláteis, matéria seca, matéria volátil, alcalinidade e ácidos gordos voláteis. A produção de biogás esperada para cada reator foi estimada a partir da degradação dos sólidos voláteis (SV destruídos). No entanto, os resultados experimentais ficaram um pouco aquém do previsto com base na degradação dos sólidos voláteis, o que pode ser atribuído a processos de inibição causados por acumulação de ácidos gordos voláteis e por consequente abaixamento do pH, mas sem descartar a possibilidade de fugas na instalação laboratorial. Comparando os diversos ensaios quanto à matéria volátil digerida, ou seja os valores de biogás esperados nos reatores em Branco e com os que continham resíduo, verificou-se que nos ensaios com 1%, 2% e 4% de resíduo, a adição de resíduos significou um potencial aumento de produção de biogás (quantidade de biogás esperado fruto da maior degradação de matéria volátil) em comparação com os reatores em branco correspondente, mas na prática não foi possível confirmar dado os problemas existentes na medição de biogás efetivamente produzido e a ocorrência de inibição em alguns reatores. Nos restantes ensaios, a adição de resíduo significou uma diminuição da quantidade de biogás esperado (menor degradação de matéria volátil) em comparação com a quantidade de biogás esperado nos reatores em branco correspondentes. Os resultados obtidos neste estudo não foram conclusivos quanto ao efeito inibidor ou potenciador de formação de biogás na codigestão do resíduo.
Solid waste, such as sewage sludge, from a wastewater treatment plant (WWTP), waste animal oils and fats, and other industrial wastes, are of particular interest, as they can be used as sources for renewable energy production. The anaerobic digestion (DA) process allows this type of waste/biomass to be converted into biogas, which can be used for the production of electrical and thermal energy, but is a complex process and depends on the properties of the biomass as well as the conditions applied to the reactor. In this context, the present study was carried out within the curricular unit "Dissertation/Project/Internship" of the Master's Degree in Sustainable Energy, in (WWTP), belonging to the SIMDOURO group - Saneamento do Grande Porto, S.A.. The main objective of the internship was to replicate at laboratory scale the anaerobic digester existing in the WWTP, and to analyze the influence of the incorporation of an industrial solid residue rich in oils and fats in the amount of biogas produced during the anaerobic digestion process from the WWTP sludge. The incorporated waste comes from a company that valuation fats and the like for the production of biodiesel. For this study different tests were carried out in parallel, in which the proportions of WWTP sludge (in this case a mixture of primary sludge and secondary sludge) were kept the same as in the actual digester, respectively 60% and 40%, with the proportion of residue added to the mixture ranged between 1% and 7%, and the percentage of inoculum, in this case digester sludge, was set at 50%. During this study, the volume of biogas produced was measured over the period of the test, which was about 15 days, or until the production of biogas ceased. Physicochemical characterization of the sludge, industrial solid residue (co-substrate) and the mixture present in each reactor was also carried out. The following parameters were determined before and after each test: pH, temperature, total solids, volatile solids, dry matter, volatile matter, alkalinity and volatile fatty acids. The expected biogas production for each reactor was estimated from the degradation of the volatile solids (SV destroyed). However, the experimental results were somewhat less than expected on the basis of the degradation of volatile solids, which can be attributed to inhibition processes caused by accumulation of volatile fatty acids and consequent lowering of the pH, but without ruling out the possibility of leaks in the laboratory installation. Comparing the various tests regarding the digested volatile matter, namely the biogas values expected in the blank tests and those that contained residue, it was verified that in the tests with 1%, 2% and 4% of residue, the addition of residue meant a potential increase in biogas production (higher quantity of biogas was expected due to the greater degradation of volatile matter) compared to the corresponding blank reactor, but in practice it was not possible to confirm it given the problems in the measurement of biogas actually produced and the occurrence of inhibition in some reactors. In the remaining tests, the addition of residue meant a decrease in the amount of biogas expected (lower degradation of volatile matter) compared to the amount of biogas expected in the corresponding blank reactors. The results obtained in this study were not conclusive concerning the inhibitory or potentiating effect of biogas formation in the codigestion of the residue.
Solid waste, such as sewage sludge, from a wastewater treatment plant (WWTP), waste animal oils and fats, and other industrial wastes, are of particular interest, as they can be used as sources for renewable energy production. The anaerobic digestion (DA) process allows this type of waste/biomass to be converted into biogas, which can be used for the production of electrical and thermal energy, but is a complex process and depends on the properties of the biomass as well as the conditions applied to the reactor. In this context, the present study was carried out within the curricular unit "Dissertation/Project/Internship" of the Master's Degree in Sustainable Energy, in (WWTP), belonging to the SIMDOURO group - Saneamento do Grande Porto, S.A.. The main objective of the internship was to replicate at laboratory scale the anaerobic digester existing in the WWTP, and to analyze the influence of the incorporation of an industrial solid residue rich in oils and fats in the amount of biogas produced during the anaerobic digestion process from the WWTP sludge. The incorporated waste comes from a company that valuation fats and the like for the production of biodiesel. For this study different tests were carried out in parallel, in which the proportions of WWTP sludge (in this case a mixture of primary sludge and secondary sludge) were kept the same as in the actual digester, respectively 60% and 40%, with the proportion of residue added to the mixture ranged between 1% and 7%, and the percentage of inoculum, in this case digester sludge, was set at 50%. During this study, the volume of biogas produced was measured over the period of the test, which was about 15 days, or until the production of biogas ceased. Physicochemical characterization of the sludge, industrial solid residue (co-substrate) and the mixture present in each reactor was also carried out. The following parameters were determined before and after each test: pH, temperature, total solids, volatile solids, dry matter, volatile matter, alkalinity and volatile fatty acids. The expected biogas production for each reactor was estimated from the degradation of the volatile solids (SV destroyed). However, the experimental results were somewhat less than expected on the basis of the degradation of volatile solids, which can be attributed to inhibition processes caused by accumulation of volatile fatty acids and consequent lowering of the pH, but without ruling out the possibility of leaks in the laboratory installation. Comparing the various tests regarding the digested volatile matter, namely the biogas values expected in the blank tests and those that contained residue, it was verified that in the tests with 1%, 2% and 4% of residue, the addition of residue meant a potential increase in biogas production (higher quantity of biogas was expected due to the greater degradation of volatile matter) compared to the corresponding blank reactor, but in practice it was not possible to confirm it given the problems in the measurement of biogas actually produced and the occurrence of inhibition in some reactors. In the remaining tests, the addition of residue meant a decrease in the amount of biogas expected (lower degradation of volatile matter) compared to the amount of biogas expected in the corresponding blank reactors. The results obtained in this study were not conclusive concerning the inhibitory or potentiating effect of biogas formation in the codigestion of the residue.
Description
Keywords
Biogás Co-substrato Digestão anaeróbia Lama de ETAR Resíduo Anaerobic digestion Biogas Co-substrate Residue WWTP sludge