Microorganisms involved in biofuel production from sygas

Miquel Pascual Arqué, Guillem Verdaguer Susín i Gerard Muntané Bisbal
Microorganisms involved in biofuel production from syngas
Introduction
There are carbon-fixing microorganisms that can convert CO, H2, and CO2 to biofuels. This process is known as syngas fermentation and it provides an attractive industrial value because it is possible to convert low cost organic substrates into valuable chemicals like biofuel. Biofuel production is important because we have to cut off our dependence on fossil fuels and microorganisms through it metabolisms are opening new roads to reach this objective. There are diferent ways to produce biofuel from syngas: producing ethanol, acetate, butyrate, hydrogen and then combusting it or doing it an electrolisis to gain energy to make electricity or running an engine.

Syngas
Syngas is the resulting gas of gasification, this process consists in raising the temperature of a material up to 700ºC without combustion. This operation is possible through the control of the oxygen and steam concentration.
Microorganisms cannot produce biofuel from straw and wood because this are hardly degradable materials, nevertheless, nowadays with gasification, we are able to produce syngas from lots of organic materials. Once syngas is produced, (that basically is mostly composed of CO,  CO2 and H2), it is added to a specific bacterias, which are capable of metabolizing the syngas into biofuel. This specific microorganisms are able to synthesise the hydrogenase enzyme, which is capable of transforming CO to larger organic compounds like short chain fatty acids and alcohols. This enzyme can break the chemical bond between the two hydrogen atoms, and this emits energy, that can be used to reduce CO to more complex organics compounds. Syngas is available from various biomasses, steel gases, MSW gasification and fossils.
Syngas is the chosen substrate to produce biofuel because it’s a gas that is composed by simple organic compounds from which it’s easy to create larger compounds and it also have hydrogen
which can be used as electron donor with the enzyme hydrogenase, the breaking of the link of diatomic hydrogen produce huge energy which is used in biosynthesis of larger organic compounds, these will be used as biofuels.

Syngas uses
This gas contains amounts of carbon monoxide and hydrogen which is converted into a gaseous fuel or liquid fuel.

Microorganisms that can produce biofuel from syngas  
Syngas can be metabolized by bacteria such as Acetobacterium woodi and Clostridium ljungdahlii. They belong to the group of strictly anaerobic, acetogenic bacteria, many of which grow on H2 + CO2 or CO or mixtures of both. These bacteria can use syngas as a source of carbon and energy.
Figura 1: metabolic via of an acetogenic where we can observe how the Hydrogenase Complex works dividing the molecule. Then this H+ creates a chemiosmotic gradient, that can synthetase ATP. This ATP and NADPH are gonna be used to reduce the CO and CO2 molecules.


For instance, the production of acetate using the Acetobacterium woodii , which is used for the synthesis of a variety of chemical products, like polyvinyl acetates. Generally, acetate is produced petrochemically. In a bioreactor under the conditions measured at a hydrogen partial pressure of 1700 mbar and a controlled pH of 7, a maximum acetate concentration of 44 g/l was reached after a process time of 11 days.
Scientists have noticed that the most important rate-limiting parameters in the autotrophic production of acetate production using Acetobacterium woodii are the pH control and the solubility of the substrate hydrogen. To improve the method, as hydrogen is poorly soluble in water the increasing hydrogen partial pressure would enhance the hydrogen concentration in the medium. Furthermore, besides the mentioned parameters, the method could be really improved using genetic. To have the genome sequence will allow identification of metabolic genes and this can drive us to metabolic modelling.
HYDROGEN
Hydrogen is the cleanest of biofuels since it is oxidized to water, with no emission of carbon dioxide in the process.
Nowadays, scientists know three main processes to produce biohydrogen. The most direct one, involves using photosynthetic microorganisms like Cyanobacteria and green algae. This photosynthetic microorganisms have the ability to split water molecules using sunlight as an energy source and produce electrons. This produced electrons, are used for energy production through electron transport chain, as well as biomass production and sugar production using anabolic reactions. (Calvin cycle). However, the electrons can also be converted to hydrogen by the action of hydrogenase enzymes. This system is really cheap because it uses water as a substrate, and sunlight as an energy source, and both of these precursors are a free inexhaustible supply. Despite the low-cost of the process there is a problem with the extreme oxygen sensitivity of hydrogenases involved in hydrogen production. Therefore the two processes (photolysis and hydrogen production) need to be temporarily uncoupled. This crucial problem is not yet solved, and no commercial application of this approach has yet been announced.
The second way of producing biohydrogen uses nitrogenase enzymes in anoxygenic photoheterotrophic microorganisms like the purple nonsulfur bacteria, for instance R. Palustris is capable of producing 7.5 ml of hydrogen/liter. The function of nitrogenase is usually to fix atmospheric N2 gas to ammonia. However, nitrogenase enzymes are also capable of producing hydrogen from electrons and protons in the absence of oxygen and presence of light.
The third process to produce hydrogen is using fermentative bacteria. There are two types: photo-fermentation and dark fermentation which produce hydrogen without using sunlight.
Dark fermentation:
This approach uses organic substrates like sugar, lignocellulosic biomass (image 2), industrial, residential, and farming waste for anaerobic fermentation. This microorganisms can use cellulose, simple sugar compounds, food waste in other words they can use anything with sugar to produce hydrogen through its oxidation . In addition, mixed culture inocula, for example microorganisms in sludge have recently been utilized to produce hydrogen from waste materials. Comparing this reactions to the light needed one, this metabolic pathway do not require light energy, so they are capable of constantly producing hydrogen from organic compounds throughout the day and night. However, production of hydrogen is only one of several electron sinks employed by fermentative microorganisms. It is estimated that only 15% of this anaerobic fermentations end with hydrogen production, next table exposes some bacterias capables of producing hydrogen by dark fermentation.

Hydrogen production by photo-fermetation:
There are some photo-heterotrofic bacteria which can produce hydrogen and CO2 from organic acids, puprle photosynthetic bacteria like Rhodobacter spheroides and Rhodobacter capsulatus can do this process.
Photo-bioreactor for bio-hydrogen production
Hydrogen aplications as biofuel:
Hydrogen can be used as fuel for cars, ships and planes because it’s so energetic. This one consists in burning hydrogen to run an engine the other way consists in gain the energy of the link breaking it with an electrolisis in specialized cells. It would be interesting if we could break the link without using extern energy, then it will be an inexhausting source of energy.
ETANOL
There are two ways to create biofuel from plant materials:
Firstly the direct fermentation which consist in the degradation of plant material to fermentable sugars and then to etanol. Ethanol can be used as fuel and in that case is biofuel.
Secondly, The indirect fermentation depends on the the burning of the plant material to syngas, then acetogenic bacteria would convert syngas (mixture of carboxide monoxide, hydrogen and carbon dioxide) to more complex carbonic compounds like ethanol.
Image 2. Obtaining ethanol from ligno-cellulosic waste

 It would be very interesting to obtain ethanol from lignocellulosic waste efficiently because it’s the most abundant material in nature and in this way we would have infinite energy.

Applications of microorganisms
The reason why the use of microorganisms it’s important for the generation of biofuels is not only for economical interests, environmental problems also needs this amount of energy. Agriculture, livestock and even human health are closely related to the dynamics of microorganisms to hold on the processes of energy generation.
The synthesis of biodiesel is normally carried out through the chemical processes of esterification and transesterification, but nowadays we have discovered a type of algae and bacteria capable of producing biodiesel in a simpler, cheaper and ecological way. It’s better to use microorganisms because we don’t have to waste energy to make more, they do the work for us without using extra energy.
Characteristics of the microorganisms used in the synthesis of bioethanol
The microorganisms to be used must meet certain needs:
- Tolerance to alcohol
- Tolerance to high temperature (40ºC)
- Tolerance to the high concentration of sugars. Working with high concentrations of sugars produces greater efficiency and productivity of the fermentation process.
- Use of mixed crops in the right proportions mixing two or more bacteria in the right proportions can favor the production of biofuel.
The production of biodiesel from algae is carried out with CO2 but now we are going to talk about how microorganisms do it and how the scientists created the ideal one mixing genes to resolve the characteristics of the microorganisms used in the synthesis of biofuel.

Conclusions
Even the combustion of biofuels is not so damaging because  uptake and conversion of gases during the fermentation will be almost equal to the amount released as CO2 during driving, so is worth it to use biofuels.
Biofuel production from will offer an ecological advantage as greenhouse gases such as CO2 and CO will be converted into industrial products.


Renewable energies that could replace non-renewable energies thanks to microorganisms and are not being carried out in a global way to avoid massive pollution caused by fossil fuels.
The results of the blog show us how these bacteria can synthesize biofuel through chemical reactions in a very effective and economic way.  The synthesis of biofuel consists always in the reduction and addition of carbon to make bigger organic compounds but the electron donor is different. This difference create lots of diferent ways to create biofuel depending on the electron donor. When syngas turns to an alcohol the electron donor is hydrogen.
It is clear that the alternatives for the production of energy in the world are given for the application since we have the raw materials necessary to carry out this technology, in addition, we have the resources for the investigation of native microorganisms with high potential or genetically modified that can transform the various substrates into others more energètic which can be used as biofuel.


Bibliography




Comentarios

  1. Unknown15 de noviembre de 2018, 3:00

    El treball està ben enfocat. Hi ha varis aspectes a millorar. En primer lloc cal que reviseu l’ortografia ja que hi ha molts errors (enzim en comptes de enzyme, entre d’altres). Cal que expliqueu millor el motiu pel qual és important la generació de biocombustibles i per què es fa a partir del syngas. Parleu de microorganismes amb aplicacions comercials, cal donar exemples. Dieu que s’han descobert nous microorganismes i que altres s’han modificat genèticament, també cal que doneu exemples. Cal incloure figures i taules per ajudar a entendre els continguts. Per exemple, per explicar el funcionament de les hidrogenases pot ajudar incloure una figura. L’apartat “Ethanol” és confós, sembla que parleu de dos processos d’obtenció de biocumbustibles: a partir del syngas i a partir de la fermentació de matèria orgànica. Cal que integreu aquesta informació a la Introducció per deixar clar que la producció de biocumbustibles pot ser a partir de diferents processos i que uns poden ser millors que altres. Igualment, l’apartat “Biogàs” cal que l’integreu en una altra secció. No té sentit fer apartats del treball que portin aquests noms. Els tres exemples que descriviu de producció d’hidrogen estan bé, cal que indiqueu la font bibliogràfica d’on els heu obtingut. Cal que aporteu imatges dels reactors on tenen lloc aquests processos i que expliqueu per quines aplicacions es fa servir l’hidrogen que es genera. Les Conclusions cal que siguin més rellevants i no tan generals. Vigileu amb les expressions com “bigger organic compounds”, seria millor dir “more complex organic compounds”.

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  2. Unknown19 de diciembre de 2018, 8:55

    Both dark fermentation and photo-fermentation have their flaws, but also some different benefits, as you exposed on this blog. In your oponion, which hydrogen production method is an easier and more realistic solution in order to reduced non-renewable sources?

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