Co-digestão de glicerol bruto e esgoto sanitário visando produção de biogás em reatores anaeróbios horizontais de leito fixo
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2022-08-19
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Universidade Estadual Paulista (Unesp)
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O aumento da demanda de energia e a diminuição da disponibilidade de combustíveis fósseis, juntamente com as crescentes preocupações com questões ambientais, impulsionaram a produção de biocombustíveis, como biodiesel e biogás. A viabilidade econômica da produção de biodiesel exige a valorização do glicerol bruto (GB), seu principal subproduto. A conversão anaeróbia do glicerol residual da produção de biodiesel tem se mostrado uma excelente opção para a produção de energia limpa a baixo custo. Devido a contaminantes presentes no GB, como metanol e sabões, e sua quantidade de matéria orgânica elevada, a co-digestão com outros resíduos é uma estratégia adotada para amenizar seu impacto na microbiota responsável pela digestão anaeróbia. Sendo constituído majoritariamente por água, o esgoto sanitário (ES) é uma excelente opção para diluir os efeitos tóxicos do GB. Neste sentido, o objetivo do presente estudo foi avaliar o emprego de diferentes proporções (v v-1) de GB e ES em quatro reatores anaeróbios horizontais de leito fixo (RAHLF) instalados em série (R1, R2, R3 e R4), em 4 ensaios distintos; 1 (1% GB), 2 (1,5% GB), 3 (2% GB) e 4 (3% GB), referente a: (i) partida do sistema e estabilidade dos reatores; (ii) melhor relação na proporção glicerol bruto e esgoto sanitário para melhoria da produção de biogás (H2 e CH4); (iii) remoção da matéria orgânica; (iv) geração de produtos de valor agregado (ácidos graxos voláteis e 1,3-Propanodiol); (v) identificação das alterações no consórcio microbiano utilizado como inóculo. O aumento do tempo de detenção hidráulica (TDH) de 0,5 para 1 dia (R1), 2,1 para 4,2 dias (R2) e 4,02 para 8,04 dias (R3) resultou em melhores produções de hidrogênio no reator R1 e metano nos reatores R2 e R3. O aumento da proporção de GB resultou em carga orgânicas volumétricas (COV) de 13,05, 18,06, 26,75 e 37,85 g DQO (L d)-1, para os ensaios 1 (1% GB), 2 (1,5% GB), 3 (2% GB) e 4 (3% GB), respectivamente. A produção de hidrogênio mais elevada no reator R1 (277,88 L H2 (m3 d)-1) ocorreu durante o ensaio 2 e no reator R2 durante o ensaio 3 (84,43 L H2 m3 d-1). A maior produção de metano foi de 312,0 L CH4 (m3 d-1) e ocorreu no reator R3 durante o ensaio 1. Nos ensaios 1 e 2 o sistema com três reatores obteve uma média de remoção de DQO de 93,6% e 98,2%, respectivamente. Após o aumento de GB para 2% no ensaio 3 a adição do reator R4 possibilitou o sistema manter uma média de remoção de 97,0% e no ensaio 4 com 3% de GB a média de remoção de DQO foi de 97,5%. Houve geração de 1,3-Propanodiol de até 4,1 g L-1 (R1 – 3% GB) e 4,8 g L-1 (R2 – 3% GB). A estratégia de co-digestão do glicerol bruto e esgoto sanitário evitou a inibição da microbiota. Além disso, houve uma mudança na abundância relativa de microrganismos entre R1, R2 e R3 e uma diminuição considerável no índice de diversidade no reator fermentativo (R1). A ordem Selenomonadales foi favorecida nos reatores R1 e R3 com o aumento do GB. A inibição das arqueias foi verificada nos reatores em série resultando na seleção da ordem Methanosarcinales. Os resultados mostraram o potencial da aplicação de reatores RAHLF em série para recuperação energética, geração de produtos de valor agregado e disposição alternativa do glicerol bruto.
Increasing energy demand and the decreasing availability of fossil fuels, along with growing concerns about environmental issues, have boosted the production of biofuels such as biodiesel and biogas. The economic viability of biodiesel production requires the valorization of crude glycerol (CG), its main by-product. The anaerobic conversion of residual glycerol from biodiesel production is an excellent option for producing clean energy at a low cost. Due to contaminants present in GB and its high amount of organic matter, co-digestion with other residues is a strategy adopted to mitigate its impact on the microbiota responsible for anaerobic digestion. Domestic sewage (DS) is an excellent option to dilute GB's toxic effects since its constitutions are most water. In this sense, the objective of the present study was to evaluate the use of different proportions (v v-1) of CG and DS in four horizontal anaerobic fixed bed reactors (HARFB) installed in series (R1, R2, R3, and R4) referring to (i) system start-up and reactor stability; (ii) better ratio in the proportion of crude glycerol and sanitary sewage to improve biogas production (H2 and CH4); (iii) removal of organic matter; (iv) generation of value-added products (volatile fatty acids and 1,3-propanediol); (v) identification of changes in the microbial consortium used as inoculum. Increasing the hydraulic retention time (HRT) from 0.5 to 1 day (R1), 2.1 to 4.2 days (R2), and 4.02 to 8.04 days (R3) resulted in better hydrogen production and methane in all reactors. The increase in the proportion of CG resulted in volumetric organic loadings (OLR) of 13.05, 18.06, 26.75 and 37.85 g COD (L d)-1, for assays 1 (1% CG), 2 (1.5% CG), 3 (2% CG) and 4 (3% CG), respectively. The highest hydrogen production in reactor R1 (277.88 L H2 (m3 d)-1) occurred during test 2 and in reactor R2 during test 3 (84.43 L H2 m3 d-1). The highest methane production was 312.0 L CH4 (m3 d-1) and occurred in reactor R3 during test 1. In tests 1 and 2, the system with three reactors obtained an average COD removal of 93.6% and 98.2%, respectively. After increasing CG to 2% in test 3, reactor R4 allowed the system to maintain an average removal of 97.0%; in test 4, with 3% of CG, the average COD removal was 97.5%. There was a generation of 1,3-Propanediol of up to 4.1 g L-1 (R1 – 3% GB) and 4.8 (R2 – 3% CG). The strategy of co-digestion of crude glycerol and domestic sewage avoided the inhibition of the microbiota. Furthermore, there was a change in the relative abundance of microorganisms between R1, R2, and R3 and a considerable decrease in the diversity index in the fermentation reactor (R1). After the increase in CG, the order Selenomonadales was favored in reactors R1 and R3. Archaea inhibition was verified in series reactors resulting in the selection of the order Methanosarcinales. The results showed the potential of applying HARFB reactors in series for energy recovery, generation of value-added products, and alternative disposal of crude glycerol.
Increasing energy demand and the decreasing availability of fossil fuels, along with growing concerns about environmental issues, have boosted the production of biofuels such as biodiesel and biogas. The economic viability of biodiesel production requires the valorization of crude glycerol (CG), its main by-product. The anaerobic conversion of residual glycerol from biodiesel production is an excellent option for producing clean energy at a low cost. Due to contaminants present in GB and its high amount of organic matter, co-digestion with other residues is a strategy adopted to mitigate its impact on the microbiota responsible for anaerobic digestion. Domestic sewage (DS) is an excellent option to dilute GB's toxic effects since its constitutions are most water. In this sense, the objective of the present study was to evaluate the use of different proportions (v v-1) of CG and DS in four horizontal anaerobic fixed bed reactors (HARFB) installed in series (R1, R2, R3, and R4) referring to (i) system start-up and reactor stability; (ii) better ratio in the proportion of crude glycerol and sanitary sewage to improve biogas production (H2 and CH4); (iii) removal of organic matter; (iv) generation of value-added products (volatile fatty acids and 1,3-propanediol); (v) identification of changes in the microbial consortium used as inoculum. Increasing the hydraulic retention time (HRT) from 0.5 to 1 day (R1), 2.1 to 4.2 days (R2), and 4.02 to 8.04 days (R3) resulted in better hydrogen production and methane in all reactors. The increase in the proportion of CG resulted in volumetric organic loadings (OLR) of 13.05, 18.06, 26.75 and 37.85 g COD (L d)-1, for assays 1 (1% CG), 2 (1.5% CG), 3 (2% CG) and 4 (3% CG), respectively. The highest hydrogen production in reactor R1 (277.88 L H2 (m3 d)-1) occurred during test 2 and in reactor R2 during test 3 (84.43 L H2 m3 d-1). The highest methane production was 312.0 L CH4 (m3 d-1) and occurred in reactor R3 during test 1. In tests 1 and 2, the system with three reactors obtained an average COD removal of 93.6% and 98.2%, respectively. After increasing CG to 2% in test 3, reactor R4 allowed the system to maintain an average removal of 97.0%; in test 4, with 3% of CG, the average COD removal was 97.5%. There was a generation of 1,3-Propanediol of up to 4.1 g L-1 (R1 – 3% GB) and 4.8 (R2 – 3% CG). The strategy of co-digestion of crude glycerol and domestic sewage avoided the inhibition of the microbiota. Furthermore, there was a change in the relative abundance of microorganisms between R1, R2, and R3 and a considerable decrease in the diversity index in the fermentation reactor (R1). After the increase in CG, the order Selenomonadales was favored in reactors R1 and R3. Archaea inhibition was verified in series reactors resulting in the selection of the order Methanosarcinales. The results showed the potential of applying HARFB reactors in series for energy recovery, generation of value-added products, and alternative disposal of crude glycerol.
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Metano, Hidrogênio, Resíduos Orgânicos, Fermentação, Resíduos Industriais