Síntese e aplicação de nanopartículas de Fe3O4, Fe0 e NiFe2O4 na digestão anaeróbia do glicerol bruto
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Data
2022-08-09
Autores
Boscaro, Mateus Eugenio [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
O uso de aditivos nanoparticulados nos processos de digestão anaeróbia de resíduos agroindustriais e os efeitos de nanopartículas metálicas em comunidades microbianas e na produção de biogás são temas de grande interesse, mas ainda pouco explorados no Brasil. A indústria do biodiesel gera como principal resíduo o glicerol bruto, que possui elevada demanda de oxigênio e quantidades substanciais de impurezas como metanol, ácidos graxos, sabões e outros compostos orgânicos e inorgânicos. Por esse motivo, o glicerol bruto tem sido utilizado por muitos pesquisadores como substrato para a produção de biogás. Sendo assim, o objetivo deste trabalho foi produzir em laboratório nanopartículas de magnetita (Fe3O4), ferro zero-valente (Fe0) e ferrita de níquel (NiFe2O4), estáveis e atóxicas e utilizá-las como aditivos em processos de digestão anaeróbia de glicerol bruto visando elevar as eficiências de geração de metano. As nanopartículas de Fe3O4 e NiFe2O4 foram sintetizadas pelo método da coprecipitação e estabilizadas com citrato ([C6H5O7]3-). As nanopartículas de Fe0 foram sintetizadas pelo método de redução de íons de ferro por borohidreto de sódio (NaBH4) e estabilizadas com citrato. As nanopartículas obtidas foram caracterizadas por Espectroscopia por Energia Dispersiva (EDS), Microscopia Eletrônica de Varredura (MEV) e Espalhamento Dinâmico de Luz (DLS). Os métodos utilizados para síntese in loco de nanopartículas produziram Fe3O4 com diâmetro inferior a 20 nm e Fe0 e NiFe2O4 com diâmetros entre 50 e 100 nm. Reatores anaeróbios em batelada de 500 mL (250 mL de volume reacional), inoculados com lodo granular anaeróbio, foram utilizados para avaliar a influência de diferentes concentrações de nanopartículas de Fe3O4, Fe0 e NiFe2O4 na digestão anaeróbia do glicerol bruto proveniente da produção de biodiesel. Reatores controle também foram montados sem a adição de nanopartículas. A produção de biogás foi quantificada pelos métodos de deslocamento de volume, a composição por cromatografia gasosa e os consumos de matéria orgânica por quantificação de demanda química de oxigênio (DQO). Nos reatores anaeróbios suplementados com nanopartículas de Fe3O4 e Fe0, em concentrações de 200, 400 e 800 mg L-1, foi observado efeito positivo na produção acumulada de metano, taxa máxima de produção de metano e remoção de DQO, quando comparados aos reatores controle. Foram verificados aumentos de 49,8% na produção acumulada de CH4 nos reatores com 200 mg-Fe3O4 L-1, de 36% da taxa máxima de produção de CH4 nos reatores com 400 mg-Fe0 L-1 e de 50% na remoção de DQO nas primeiras 170 horas de operação nos reatores com 200 mg-Fe0 L-1. Nanopartículas de NiFe2O4 não apresentaram efeito significativo na digestão anaeróbia do glicerol bruto para os reatores com 200 e 400 mg-NiFe2O4 L-1. Além disso, foi verificado efeito deletério, com redução de 30% na produção de metano e remoção de DQO nos reatores operados com 800 mg-NiFe2O4 L-1. Também foi observado aumento substancial na abundância relativa dos Domínios Bacteria e Archaea, especialmente as ordens Bacteroides, Clostridiales, Methanomicrobiales e Methanosarcinales, após suplementação com nanopartículas de Fe3O4. A adição de nanopartículas de Fe3O4 favoreceu as comunidades de bactérias e arqueias envolvidas no consumo do glicerol, elevando a produção de CH4.
The use of nanoparticulate additives in anaerobic digestion of agroindustrial residues and the effects of metallic nanoparticles on microbial communities and biogas production are topics of great interest today, but still poorly explored in Brazil. The biodiesel industry generates crude glycerol as its major residue, which has high oxygen demand and substantial amounts of impurities such as methanol, fatty acids, soaps and other organic and inorganic compounds. For this reason, crude glycerol has been used by many researchers as a substrate for biogas production. Therefore, this work aimed to produce stable and non-tóxic magnetite (Fe3O4), zero-valent iron (Fe0) and nickel ferrite (NiFe2O4) nanoparticles and use them as additives in anaerobic digestion of crude glycerol aiming to increase methane generation efficiencies. Fe3O4 and NiFe2O4 nanoparticles were synthesized by the coprecipitation method and stabilized with citrate ([C6H5O7]3-). Fe0 nanoparticles were synthesized by the method of iron ions reduction using sodium borohydride (NaBH4) and stabilized with citrate. Nanoparticles were characterized by Energy Dispersive X-Ray Spectroscopy (EDS), Scanning Electron Microscopy (SEM) and Dynamic Light Scattering (DLS). The methods designed for in loco synthesis produced Fe3O4 nanoparticles with diameters below 20 nm and Fe0 and NiFe2O4 nanoparticles with diameters between 50 and 100 nm. Anaerobic batch reactors (250 mL reaction volume), filled with anaerobic granular sludge, were used for assessing the influence of different concentrations of Fe3O4, Fe0 and NiFe2O4 nanoparticles on the anaerobic digestion of crude glycerol from biodiesel production. Control reactors were also assembled without the addition of nanoparticles. Biogas production was quantified by water displacement method and gas chromatography and substrate consumption was evaluated by COD analysis. In anaerobic batch reactors containing Fe3O4 and Fe0 nanoparticles, in concentrations of 200, 400 and 800 mg L-1 a positive effect was observed in the total volume of methane, maximum rate of methane production and COD removal, in relation to control reactors. There were increases of 49.8% in the accumulated production of CH4 in reactors with 200 mgFe3O4 L-1, 36% in the maximum rate of CH4 production in reactors with 400 mgFe0 L-1 and 50% of COD removal in the first 170 hours of operation in reactors with 200 mgFe0 L-1. NiFe2O4 nanoparticles had no significant effect on the anaerobic digestion of crude glycerol in reactors with 200 and 400 mg NiFe2O4 L-1 and had a deleterious effect, with 30% reduction in methane production and COD removal, in reactors with 800 mg NiFe2O4 L-1. It was also observed a substantial increase on relative abundance of Bacteria and Archaea Domains, specially Bacteroides, Clostridiales, Methanomicrobiales and Methanosarcinales orders, after anaerobic digestion supplemented with Fe3O4 nanoparticles. The addition of Fe3O4 nanoparticles could improve and optimizes bacterial and archaeal communities involved in glycerol consumption, enhancing the CH4 production.
The use of nanoparticulate additives in anaerobic digestion of agroindustrial residues and the effects of metallic nanoparticles on microbial communities and biogas production are topics of great interest today, but still poorly explored in Brazil. The biodiesel industry generates crude glycerol as its major residue, which has high oxygen demand and substantial amounts of impurities such as methanol, fatty acids, soaps and other organic and inorganic compounds. For this reason, crude glycerol has been used by many researchers as a substrate for biogas production. Therefore, this work aimed to produce stable and non-tóxic magnetite (Fe3O4), zero-valent iron (Fe0) and nickel ferrite (NiFe2O4) nanoparticles and use them as additives in anaerobic digestion of crude glycerol aiming to increase methane generation efficiencies. Fe3O4 and NiFe2O4 nanoparticles were synthesized by the coprecipitation method and stabilized with citrate ([C6H5O7]3-). Fe0 nanoparticles were synthesized by the method of iron ions reduction using sodium borohydride (NaBH4) and stabilized with citrate. Nanoparticles were characterized by Energy Dispersive X-Ray Spectroscopy (EDS), Scanning Electron Microscopy (SEM) and Dynamic Light Scattering (DLS). The methods designed for in loco synthesis produced Fe3O4 nanoparticles with diameters below 20 nm and Fe0 and NiFe2O4 nanoparticles with diameters between 50 and 100 nm. Anaerobic batch reactors (250 mL reaction volume), filled with anaerobic granular sludge, were used for assessing the influence of different concentrations of Fe3O4, Fe0 and NiFe2O4 nanoparticles on the anaerobic digestion of crude glycerol from biodiesel production. Control reactors were also assembled without the addition of nanoparticles. Biogas production was quantified by water displacement method and gas chromatography and substrate consumption was evaluated by COD analysis. In anaerobic batch reactors containing Fe3O4 and Fe0 nanoparticles, in concentrations of 200, 400 and 800 mg L-1 a positive effect was observed in the total volume of methane, maximum rate of methane production and COD removal, in relation to control reactors. There were increases of 49.8% in the accumulated production of CH4 in reactors with 200 mgFe3O4 L-1, 36% in the maximum rate of CH4 production in reactors with 400 mgFe0 L-1 and 50% of COD removal in the first 170 hours of operation in reactors with 200 mgFe0 L-1. NiFe2O4 nanoparticles had no significant effect on the anaerobic digestion of crude glycerol in reactors with 200 and 400 mg NiFe2O4 L-1 and had a deleterious effect, with 30% reduction in methane production and COD removal, in reactors with 800 mg NiFe2O4 L-1. It was also observed a substantial increase on relative abundance of Bacteria and Archaea Domains, specially Bacteroides, Clostridiales, Methanomicrobiales and Methanosarcinales orders, after anaerobic digestion supplemented with Fe3O4 nanoparticles. The addition of Fe3O4 nanoparticles could improve and optimizes bacterial and archaeal communities involved in glycerol consumption, enhancing the CH4 production.
Descrição
Palavras-chave
Metanogênese, Reatores anaeróbios, Glicerol bruto, Magnetita, Ferro zero- valente, Ferrita de níquel, Sequenciamento, Consórcios anaeróbios, Methanogenesis, Anaerobic reactors, Crude glycerol, Magnetite, Zerovalent iron, Nickel ferrite, Sequencing, Anaerobic consortium