Estudo do crescimento e controle de biomassa na produção de biohidrogênio a partir da fermentação escura de vinhaça de cana-de-açúcar usando reatores contínuos de tubos múltiplos
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Data
2022-05-27
Autores
Grangeiro, Luana Cardoso [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Estudos mostram que a perda de desempenho em sistemas fermentativos após 20 dias de operação pode estar associada ao crescimento inadequado de microrganismos, resultando em excesso ou falta de biomassa nos reatores. O parâmetro que permite medir a relação alimento/microrganismo e consequentemente controlar a biomassa nos reatores é chamado de carga orgânica volumétrica específica (COVe). Desta forma, desenvolver um projeto de reator que permita o controle adequado da COVe pode ser um fator chave na produção de biohidrogênio (BioH2) a longo prazo. Neste contexto, os reatores contínuos de tubos múltiplos (RCTMs) tem se destacado como uma tecnologia promissora devido à sua estrutura fornecer uma região de tubos para fixação da biomassa microbiana, sem utilização de material suporte e ainda permitir a manutenção da COVe, por meio do descarte contínuo da biomassa. Nesta sequência, o objetivo desta pesquisa foi estudar RCTMs com 10 (RCTM10) e 18 (RCTM18) tubos no controle de processo em função da COVe. Na primeira etapa, o RCTM18 foi operado sob condição mesofílica de temperatura (25°C), inoculado por processo de autofermentação e alimentado com água residuária sintética, à base de sacarose como fonte de carbono. Os resultados mostraram que o RCTM18 apresentou o controle adequado de COVe (3,3 – 6,33 gDQOg-1SSV d-1), porém apresentou baixo rendimento médio de hidrogênio (0,043 ± 0,006 molH2.molCH-1), com uma produção volumétrica máxima igual a 415,1 ± 422,1 mLH2 L-1d-1, em faixa de operação de pH 4-5,5. Na segunda etapa, os RCTMs sob condições termofílicas de temperatura (55°C) foram inoculados por processo de autofermentação e alimentados com vinhaça de cana-de-açúcar, como fonte de carbono. O RCTM18 apresentou o melhor resultado no controle da COVe (2,0 - 8,0 gDQO.g-1SSV.d-1) em comparação com o RCTM10 (0,5 – 4,0 gDQO g-1SSV d-1), e semelhante a faixa ótima (2,0 - 7,0 gDQO.g-1SSV.d-1) encontrada na literatura. O RCTM18 (0,0006 ± 0,014 molH2.gDDQO-1) e o RCTM10 (0,0013 ± 0,003 molH2.gDQO-1) apresentaram rendimentos médios de hidrogênio quase nulos. Na terceira etapa, as biomassas acidogênicas dos RCTMs obtidas na operação contínua foram testadas em reatores em modo batelada, as quais produziram hidrogênio e ácidos orgânicos. A quarta e última etapa consistiu no estudo de biologia molecular para a quantificação de metabólitos e caracterização da microbiota, o qual apresentou valores de abundância relativa ao gênero Clostridium sensu stricto 7 (19,87%) no RCTM10 e Bacillus (18,32%) no RCTM18. Isto permitiu a discussão e fundamentação dos resultados desta pesquisa, verificando que os RCTMs se mostraram configurações com potencial para o controle da COVe em meio sintético e vinhaça de cana-de-açúcar, sem a necessidade de descarte de biomassa ou material suporte para adesão dos microrganismos.
Studies have shown that the loss of performance after 20 days of operation may be associated with factors such as inadequate growth of microorganisms (excess or lack of biomass in the reactors). The specific organic loading rate (SOLR) is the parameter that allows to measure the food/microorganism ratio and consequently control the biomass in the reactors. Thus, developing a reactor design that allows adequate control of the SOLR may be a key factor in long-term BioH2 production. Based in this background, continuous multiple tube reactors (CMTRs) have stood out as a promising technology due to their structure providing a region of tubes for microbial biomass retention, without the use of support material and also allowing the maintenance of the SOLR, by continuous biomass disposal. Accordingly, the aim of this study was to evaluate the performance of two CMTRs with different number of tubes in controlling SOLR. At first step, the control reactor (CR) and the CMTR18 was operated under mesophilic temperature conditions (25°C), inoculated by a natural fermentation process and fed with synthetic wastewater based on sucrose as the carbon source. The results showed the CMTR18 presents the adequate SOLR control (3,3 – 6,33 gCDO g-1SSV d-1) but showed low yield of hydrogen (0,043 ± 0,006 molH2.molCH-1), maximum volumetric production equal 415,1 ± 422,1 mLH2 L-1d-1, working in a range of pH pH 4-5,5. At second step, CMTRs with 10 and 18 tubes were operated under thermophilic temperature conditions (55°C), inoculated by a natural fermentation process and fed with sugarcane wastewater. The CMTR18 presented the best performance in the SOLR (2,0 - 8,0 gDQO.g-1SSV.d-1) relate to CMTR10 (0,5 – 4,0 gDQO g-1SSV d-1), and similar to the optimal SOLR control range found in the literature (2,0 - 7,0 gDQO.g-1SSV.d-1). CMTR18 (0,0006 ± 0,014 molH2.gDDQO-1) and CMTR10 (0,0013 ± 0,003 molH2.gDQO-1) have obtained average yields of hydrogen near zero. At third step, the acidogenic biomasses produced in the CMTRs were tested in batch mode reactors to check the hydrogen production potential of these biomasses. The final step consisted of the molecular biology study for the quantification of metabolites and characterization of the microbiota in strategic points of all operations, which presented values of relative abundance to the genus Clostridium sensu stricto 7 (19.87%) in CMTR and Bacillus (18.32%) in CMTR18. This allowed the discussion and substantiation of the results of this research, verifying that the CMTRs showed configurations with potential for the control of SOLr in synthetic medium and sugarcane vinasse, without the need to discard biomass or support material for adhesion of microorganisms.
Studies have shown that the loss of performance after 20 days of operation may be associated with factors such as inadequate growth of microorganisms (excess or lack of biomass in the reactors). The specific organic loading rate (SOLR) is the parameter that allows to measure the food/microorganism ratio and consequently control the biomass in the reactors. Thus, developing a reactor design that allows adequate control of the SOLR may be a key factor in long-term BioH2 production. Based in this background, continuous multiple tube reactors (CMTRs) have stood out as a promising technology due to their structure providing a region of tubes for microbial biomass retention, without the use of support material and also allowing the maintenance of the SOLR, by continuous biomass disposal. Accordingly, the aim of this study was to evaluate the performance of two CMTRs with different number of tubes in controlling SOLR. At first step, the control reactor (CR) and the CMTR18 was operated under mesophilic temperature conditions (25°C), inoculated by a natural fermentation process and fed with synthetic wastewater based on sucrose as the carbon source. The results showed the CMTR18 presents the adequate SOLR control (3,3 – 6,33 gCDO g-1SSV d-1) but showed low yield of hydrogen (0,043 ± 0,006 molH2.molCH-1), maximum volumetric production equal 415,1 ± 422,1 mLH2 L-1d-1, working in a range of pH pH 4-5,5. At second step, CMTRs with 10 and 18 tubes were operated under thermophilic temperature conditions (55°C), inoculated by a natural fermentation process and fed with sugarcane wastewater. The CMTR18 presented the best performance in the SOLR (2,0 - 8,0 gDQO.g-1SSV.d-1) relate to CMTR10 (0,5 – 4,0 gDQO g-1SSV d-1), and similar to the optimal SOLR control range found in the literature (2,0 - 7,0 gDQO.g-1SSV.d-1). CMTR18 (0,0006 ± 0,014 molH2.gDDQO-1) and CMTR10 (0,0013 ± 0,003 molH2.gDQO-1) have obtained average yields of hydrogen near zero. At third step, the acidogenic biomasses produced in the CMTRs were tested in batch mode reactors to check the hydrogen production potential of these biomasses. The final step consisted of the molecular biology study for the quantification of metabolites and characterization of the microbiota in strategic points of all operations, which presented values of relative abundance to the genus Clostridium sensu stricto 7 (19.87%) in CMTR and Bacillus (18.32%) in CMTR18. This allowed the discussion and substantiation of the results of this research, verifying that the CMTRs showed configurations with potential for the control of SOLr in synthetic medium and sugarcane vinasse, without the need to discard biomass or support material for adhesion of microorganisms.
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Palavras-chave
Fermentação escura, Biomassa microbiana, Carga orgânica volumétrica específica, Vinhaça de cana-de-açúcar