Exploring syntrophic relationships in the anaerobic biodegradation of lipids and long chain fatty acids

ICBM-3 - 3rd International Conference on Biogas Microbiology (Abstract Book)[Excerpt] Practical knowledge on anaerobic digestion of waste lipids has been improving for several decades, but the microbiology of these processes remains partially undisclosed, with non-cultivated taxonomic groups often detected in anaerobic communities degrading lipids. This work studies the diversity and physiology of anaerobic microorganisms involved in the metabolism of lipids and long chain fatty acids. Anaerobic culturing procedures were applied for the development of enrichment cultures, and combined with next generation sequencing techniques. Enriched microbial communities specialized in the degradation of triolein (0.3 mmol·L-1) and oleate (1 mmol·L-1) were obtained under methanogenic conditions. Oleatedegrading cultures were also developed in the presence of the external electron acceptors ferric hydroxide (75 mmol·L-1) or sulfate (15 mmol·L-1). Three mesophilic sludges from different origins were used as inocula. [...]info:eu-repo/semantics/publishedVersio

Perspectives on syngas fermentation

Book of Abstracts of CEB Annual Meeting 2017The replacement of fossil fuels by renewable energy sources is, nowadays, a worldwide priority. Gasification processes and further bioconversion of syngas appears to be a promising alternative compared to the existing chemical techniques, since this process convert renewable sources into alternative fuels and commodity chemicals, such as CH4, fatty acids, alcohols, etc., additionally contributing to the reduction of greenhouse gases [1]. Nearly any form of organic matter can be transformed through gasification, into syngas, mainly composed of CO, H2 and CO2. The biological conversion of syngas offers several advantages over catalytic processes, specifically the greater resistance to catalyst poisoning and the higher specificity for the substrates [2]. Syngas- and CO-fermenting microorganisms use the Wood-Ljungdahl pathway to produce several multi-carbon compounds such as short- and medium-fatty acids and alcohols. Even though many studies were performed in the last few years, fermentation of syngas still involves practical challenges due to limitations of the process. The major bottleneck of syngas fermentation that blocks the commercialization of this technology is gas-to-liquid mass transfer limitations, since it reduces the microorganisms access to the substrate and consequently reduces the productivity rates. It is of utmost importance the development of alternatives that promote the enhancement of mass transfer, the improvement on the productivity rates from syngas fermentation and the deep study of the biocatalysts involved in syngas bioconversion pathways. Biological syngas conversion has been a research topic at the BRIDGE group since 2009, by studying both technological and microbiological aspects of the process. Previous work developed in our group focused on the use of anaerobic complex microbial communities to obtain enriched cultures and/or pure cultures that could convert syngas or CO into mainly acetate, CH4 and H2. Regarding to the technological aspects of syngas bioconversion process, a multi-orifice baffled bioreactor was used to study the effect of using different reactors designs to improve the gas-liquid mass transfer. Moreover, recent studies conducted at BRIDGE group with collaboration of BIOSYSTEMS group showed that the use of increased pressure (up to 5 bar) to increase gas-liquid mass transfer, leads to different metabolic routes on microorganisms. These results represent a step forward to direct the biochemical pathways of microbial community towards the specific products from syngas. As future perspectives, we aimed to continue a research line on syngas fermentation, by studying different operational approaches for this process and focusing on the production of butanol, 2,3-butanediol and propionate.info:eu-repo/semantics/publishedVersio

Fermentação de gás de síntese usando sistemas pressurizados

Tese de doutoramento em Chemical and Biological EngineeringOne of the major drawbacks of syngas fermentation is the limited gas-liquid mass transfer that generally limits productivities. Most research has been focusing in increasing the kLa (volumetric gas-liquid mass transfer coefficient), investigating different reactor typologies and gas dispersion devices. However, the driving force for mass transfer can also be increased, for instance, by operating at increased pressure. This thesis aims to explore the effect of increased pressure in syngas fermentation to improve the gas solubility, evaluating the effect on the biocatalysts and on the process itself. The starting point of this work was to use an adapted culture (from a syngas converting reactor) as inoculum. This culture was able to mainly produce methane and acetate from syngas. Methane was not produced directly from CO, but via the conversion of acetate and H2 by the bacteria present in the mixed culture (Acetobacterium and Sporomusa species). Later on, this culture was subsequentially transferred with syngas, originating an enriched culture mainly composed by Acetobacterium and Methanospirillum species that, besides acetate and methane, was able to produce propionate from syngas. From that highly enriched culture a new strain of Acetobacterium wieringae, strain JM, was isolated and characterized. This highly enriched culture was tested in an axial agitation reactor (AAR) with different initial syngas (CO, H2 and CO2 (60:30:10 %, v/v)) pressures, from 100 kPa to 600 kPa. No substrate inhibition was observed, even at the highest pressure and an increase of 45 % in titres (of acetate and propionate) were obtained. Moreover, the increase of pressure resulted in a shift in the metabolic pathways from acetate towards propionate, which is an uncommon product of syngas fermentation. The effect of pressure on the conversion of syngas by anaerobic mixed sludge was then studied using two different reactor typologies, AAR and GLR (gas-lift reactor). Initial syngas pressures of 100 kPa, 300 kPa and 500 kPa were tested. Overall, the GLR showed better performance in terms of CO consumption rates and product titres. The main product obtained was methane and the results showed, for the first time, that methanogenic activity was not inhibited with initial syngas pressures up to 500 kPa, achieving methane yields of 75 % for the GLR, and 92 % for the AAR. At 300 kPa and 500 kPa, volatile fatty acids were also produced, namely acetate, proprionate and n-butyrate. Propionate was the most abundant acid produced, reaching 4.4 mM at 300 kPa and 4.8 mM at 500 kPa in the AAR. Overall, the use of moderate pressures in syngas fermentation was shown beneficial, as it resulted in better productivities and titres without having significant detrimental effects on cell growth. The increase of pressure also did not inhibit methanogenesis. Moreover, higher pressures seem to induce the production of different chemicals, broadening the product spectrum of syngas fermentation. In this way, these findings could be the basis of new developments in the industrialization of syngas fermentation to produce platform chemicals and/or for biomethanation processes.Um dos principais desafios da fermentação do gás de síntese é a limitação na transferência de massa gás-líquido que geralmente limita a produtividade. A maioria das pesquisas têm-se concentrado no aumento do kLa (coeficiente de transferência de massa gás-líquido volumétrico), investigando diferentes tipologias de reatores e dispositivos de dispersão de gás. No entanto, a força motriz para a transferência de massa também pode ser aumentada, por exemplo, operando sistemas pressurizados. Esta tese tem como objetivo explorar o efeito do aumento da pressão na fermentação de gás de síntese para melhorar a solubilidade do gás, avaliando o efeito nos biocatalisadores e no próprio processo. O ponto de partida deste trabalho foi a utilização de uma cultura adaptada (de um reator de conversão de gás de síntese) como inóculo. Essa cultura foi capaz de produzir principalmente metano e acetato a partir do gás de síntese. O metano não foi produzido diretamente do CO, mas através da conversão de acetato e H2 pelas bactérias presentes na cultura mista (espécies dos géneros Acetobacterium e Sporomusa). Essa cultura foi consecutivamente transferida usando gás de síntese como substrato, originando uma cultura enriquecida composta principalmente por espécies de Acetobacterium e de Methanospirillum que, além de acetato e metano, foi capaz de produzir propionato a partir de gás de síntese. A partir dessa cultura altamente enriquecida, uma nova strain de Acetobacterium wieringae, strain JM, foi isolada e caracterizada. Esta cultura altamente enriquecida foi testada num reator de agitação axial (AAR) com diferentes pressões de gás de síntese (CO, H2 e CO2 (60:30:10%, v/v)), de 100 kPa a 600 kPa. Não foi observada qualquer inibição pelo substrato, mesmo na pressão mais elevada e obteve-se um aumento de 45 % na produção final de acetato e propionato. Além disso, o aumento da pressão originou um desvio metabólico de acetato para propionato, que é um produto incomum da fermentação do gás de síntese. O efeito da pressão na conversão de gás de síntese utilizando biomassa anaeróbia foi também estudado usando duas tipologias de reatores diferentes, AAR e GLR (reator gas-lift). Foram testadas as seguintes pressões iniciais de gás de síntese: 100 kPa, 300 kPa e 500 kPa. O GLR apresentou melhor desempenho em termos de taxas de consumo de CO e de concentração final de produtos. O principal produto obtido foi o metano e os resultados mostraram, pela primeira vez, que a atividade metalogénica não foi inibida com pressões iniciais de syngas de até 500 kPa, atingindo rendimentos de metano de 75 % para o GLR e 92 % para o AAR. A 300 kPa e 500 kPa, também foram produzidos ácidos gordos voláteis, nomeadamente, acetato, propionato e n-butirato. O propionato foi o ácido mais abundante produzido, atingindo 4,4 mM a 300 kPa e 4,8 mM a 500 kPa no AAR. No geral, o uso de pressões moderadas na fermentação do gás de síntese mostrou-se benéfico, pois resultou em melhores produtividades e concentrações finais de produto sem ter efeitos prejudiciais significativos no crescimento celular. O aumento da pressão também não inibiu a metanogénese. Além disso, pressões mais altas parecem induzir a produção de diferentes produtos químicos, ampliando o espectro de produtos da fermentação do gás de síntese. Desta forma, estas descobertas podem ser a base de novos desenvolvimentos na industrialização da fermentação do gás de síntese para a produção de produtos químicos e/ou para processos de biometanação