This is how our technology can be implemented:
By converting the waste gas CO2 into the biofuel butanol using our engineered bacteria, we want to contribute/oder: we make a first step to a carbon-neutral future. For this purpose, industrial waste gas will be directly funnelled into the bacterial fermenter to serve as an energy and carbon source for the metabolic processes of our bacteria. The fermentation product butanol can then be distributed by the existing fossil fuel infrastructure, and function as biofuel in combustion engines or in the chemical industry.
With our project we aim to form the basis for the industrial production of biobutanol. After the introduction of the Wood-Ljungdahl pathway into our target Clostridium, further metabolic studies will be required to determine how metabolism can be designed to increase biofuel production from CO2. Once the bacterium with the desired metabolic flux is generated, the scalability of the process must be investigated. As bacterial cultivation shows differences dependent on the culture volume, improvements might be required here.
As stated above, we aim to utilise the synthesis gas as produced by Municipal waste gasification or in the steel industry. A major challenge is, that the exact gas content of many waste gases , is unknown and depends on the material burned. In addition, the amount of gas that is produced, varies immensely, depending on the production step, even in steel production which yields relatively constant gas compositions. For our purpose, filters are required to get rid of highly toxic trace gases which could harm our bacterial culture. The first industrial scale application of the Wood-Ljungdahl pathway by LanzaTech, has shown that Clostridia can be adapted to changing gas supply and that they are able to cope with this challenge without drastically reducing the productivity of the culture. In fact, LanzaTech has already built four production plants which are directly connected to the exhaust system of waste gasification plants This demonstrates that the technology that is necessary to scale up our project, is already available and feasible. Apart from simple filtering for trace gases, no extensive measures are required, and the gas can directly be vented to the culture. Additionally, the Wood-Ljungdahl pathway can solely be fueled by CO which provides even wider application. For this purpose, we spoke to a young start-up (Ucaneo) which is targeting new membranes for carbon gas capture (due to the state of the start-up we limit the informations at this point). An additional advantage is that the substrate is very cheap as only few companies utilise this gas mixture and most companies pay for it’s disposal.
Both the Wood-Ljungdahl donor strain as well as the butanol producing recipient strain are scientifically well characterised and accurate numbers for the metabolic turn-over from gas to substrate are known. However, it is very difficult to predict a turn-over rate for the bacterial strain we aim to engineer, as it has not yet been investigated how this type of bacteria reacts to the assumed completion of the WLP . Clostridia also require a sophisticated energy production system which can limit the turn-over capability. Nevertheless, we aim to achieve similar product formation rates to the original recipient strain (as we can provide an oversupply of substrate). Since syngas or CO/CO2 act as energy and carbon source, only simple cultivation media are required containing primarily trace elements for enzymes. Furthermore, the bacteria are cultivated at ambient temperatures around 30°C, keeping the energy costs low compared to chemical fuel synthesis. The utilised bacteria are strictly anaerobic which limits our choice for fermentation plants. However, systems are already commercially available.
The bacterial strain that is utilised as recipient strain, produces butanol by the well established aceton, butanol, ethanol (ABE)- Pathway. The ratio of the originally described pathway is 3:6:1 (aceton:butanol:ethanol). However, great efforts are being made in the field of metabolic engineering to shift the ratio towards butanol. Butanol can be extracted from this mixture by e.g. ionic liquids, membrane extraction, liquid-liquid extraction, or gas-stripping. As the ABE-pathway has been biotechnologically known for a long time, the extraction methods are well developed and produce high rates. Aceton and ethanol can be sold as well,although they are less valuable than butanol.
Butanol is a liquid solvent that can be readily dispersed in a manner similar to fossil fuels. It can be stored over longer periods of time and utilised in internal combustion engines or in the chemical industry. As it has a lower price point than fossil fuels and doesn’t require further processing, biobutanol can serve as climate friendly fuel in internal combustion engines. It is important to note that this technology would generate a climate friendly fuel alternative that is also capable of moving heavy machinery as cargo ships and aeroplanes. In this area, electrification has not provided the desired results.