Biogas Upgrading Through a Microalgae Platform

Abstract

As emissões globais de gases de efeito de estufa aumentaram nas últimas décadas, sendo o setor energético o principal responsável. Aumentar a quota de energia renovável utilizando novas tecnologias mais verdes é um dos principais focos da União Europeia para as próximas décadas, com o grande objetivo de atingir emissões-zero até 2050. O REPowerEU é uma das estratégias para aumentar a produção de energias renováveis e a poupança de energia, reduzindo ainda a independência energética do gás proveniente da Rússia. Uma das iniciativas propostas é o aumento da produção de biogás e a sua conversão para biometano, para injeção nas redes de gás já existentes, até 2030. As microalgas têm vindo a surgir como uma potencial tecnologia de conversão do biogás devido à sua elevada atividade fotossintética, consumindo CO2 enquanto geram biomassa que pode originar produtos de valor acrescentado.Esta dissertação centrou-se na melhoria de biogás utilizando uma plataforma de microalgas, que consistiu numa cultura de Chlorella vulgaris NIVA CHL-108, num depósito IBC (International Bulk Container). O processo consistiu no arejamento da cultura com biogás proveniente de outro IBC, que funcionou como um digestor anaeróbio. Este sistema piloto foi criado pela Algaementum e instalado na Monte Silveira Bio, uma quinta com certificação biológica desde 1999. A matéria-prima da digestão anaeróbia consistiu em estrume de vaca e a monitorização do biogás produzido pelo sistema iniciou no dia 23 e terminou no dia 51. Os resultados mostraram um valor máximo de produção de 52.8% de CH4 no biogás bruto, sendo os restantes valores inferiores a 40%. O sistema mostrou não satisfazer o processo de melhoria do biogás, tendo todo o biogás proveniente da digestão anaeróbia solubilizado na cultura, devido à falta de fluxo inerente à operação do sistema. Foram realizados alguns ensaios em contentores mais pequenos e utilizando outras matérias-primas (Opuntia Ficus Indica e cultura de microalgas).Realizou-se ainda a caracterização final da biomassa de microalgas, que mostrou diferenças na cultura entre os dias 28 e 40 de monitorização. O teor de proteínas aumentou de 19.15% para 25.91%, enquanto o teor de lípidos aumentou apenas de 1.05% para 1.45%. A concentração de clorofila no dia 40 foi de 9.42 mg/L, aumentando desde o dia 28, em que registou uma concentração de 4.32 mg/L.Este novo sistema de cultivo de microalgas mostra, assim, algum potencial, visto que as propriedades da cultura de microalgas foram melhoradas utilizando um IBC, cujos custos, comparados aos de um fotobiorreator, são muito inferiores.

Global greenhouse gas emissions have increased in the last decades and the energy sector is the main responsible.Thus,the need to pursue new green technologies and expand the share of renewable energy is one of the main focuses of the European Union for the next few decades,with the grand objective of reaching net-zero emissions by 2050.The REPowerEU is one of the strategies to increase renewable production and energy saving,and seeks energy independence from Russian gas, following recent events.One of the initiatives proposed is the increase in biogas production,and its upgrading to biomethane,for injection in the already existing gas grids,until 2030.Microalgae have been surging as a potential biogas upgrading technology because of its high photosynthetic activity,capturing CO2 whilst growing biomass that can generate high value-products.This dissertation focused on the upgrading of biogas using a microalgae platform,which consisted in an International Bulk Container (IBC) filled with a Chlorella vulgaris NIVA CHL-108 culture.The process consisted in aerating the culture with biogas. Another IBC was set up, working as an anaerobic digestor.The biogas resulting from the anaerobic digestion (AD) also served as a carbon source for microalgae culture in the process.This pilot system was created by Algaementum and was set up in Monte Silveira Bio,a certificated organic farm since 1999.The AD feedstock consisted in the farm’s cattle manure.Biogas monitorization was initiated on the 23rd day following the pilot setup.Results showed a peak production value of 52.8% CH4 raw biogas, with the remaining values below 40%. The system operation was unsuccessful regarding the biogas upgrading process, as all the biogas solubilized in the culture, due to low AD biogas flux.Some trials were performed in smaller containers and using other feedstocks (OFI and microalgae culture.A final characterization of the microalgae biomass was performed,which showed differences in the culture between days 28 and 40 of the monitorization period.Protein content increased from 19.15% to 25.91% and lipids content increased slightly,from 1.05% to 1.45%.Chlorophyll a concentration was 9.42 mg/L in day 40,an increase from day 28,when the value was 4.32 mg/L.Thus,this method of cultivating microalgae offers great potential,since there was an improvement in the microalgal biomass properties,in an IBC system, and the costs involved in IBC processes are much lower than those of photobioreactors (PBRs).Global greenhouse gas emissions have increased in the last decades and the energy sector is the main responsible.Thus,the need to pursue new green technologies and expand the share of renewable energy is one of the main focuses of the EU for the next few decades,with the grand objective of reaching net-zero emissions by 2050. The REPowerEU is one of the strategies to increase renewable production and energy saving,and seeks energy independence from Russian gas,following recent events.One of the initiatives proposed is the increase in biogas production,and its upgrading to biomethane,for injection in the already existing gas grids,until 2030.Microalgae have been surging as a potential biogas upgrading technology because of its high photosynthetic activity, capturing CO2 whilst growing biomass that can generate high value-products.This dissertation focused on the upgrading of biogas using a microalgae platform,which consisted in an International Bulk Container (IBC) filled with a Chlorella vulgaris NIVA CHL-108 culture.The process consisted in aerating the culture with biogas.Another IBC was set up,working as an anaerobic digestor.The biogas resulting from the anaerobic digestion (AD) also served as a carbon source for microalgae culture in the process.This pilot system was created by Algaementum and was set up in Monte Silveira Bio,a certificated organic farm since 1999.The AD feedstock consisted in the farm’s cattle manure.Biogas monitorization was initiated on the 23rd day following the pilot setup.Results showed a peak production value of 52.8% CH4 raw biogas,with the remaining values below 40%. The system operation was unsuccessful regarding the biogas upgrading process,as all the biogas solubilized in the culture,due to low AD biogas flux.Some trials were performed in smaller containers and using other feedstocks(OFI and microalgae culture).A final characterization of the microalgae biomass was performed,which showed differences in the culture between days 28 and 40 of the monitorization period.Protein content increased from 19.15% to 25.91% and lipids content increased slightly,from 1.05% to 1.45%. Chlorophyll a concentration was 9.42 mg/L in day 40,an increase from day 28,when the value was 4.32 mg/L.Thus,this method of cultivating microalgae offers great potential,since there was an improvement in the microalgal biomass properties,in an IBC system, and the costs involved in IBC processes are much lower than those of photobioreactors (PBRs).