Ideas Come True
Fig 1. Flow chart of E. coli carbon utilization system
- Control System
In this project, we, the NCKU Tainan Team, have proposed an alternative way to reduce the emission of Carbon dioxide (CO2). Referring to the opinions and feedbacks from many industry experts and professors, we design a new factory flow to capture CO2 by E. coli Not only our device meets the specs to commercialize, but it also demonstrates high cost performance.
The emission of CO2 has been a serious problem for a century that causes global warming and severe climate change. Even though many ways have been tried to reduce it, the generation of CO2 primarily from industry is still overwhelming. Therefore, scientists and governments have been working hard to find solutions to tackle the problem.
Fig 2. Overview of the control system
There are many aspects we need to consider. First, we calculate the emission velocity of CO2 from the factory, as well as the medium exchange rate and the growth rate of E. coli.
Fig 1. is a process of whole E. coli carbon utilization that we design for industrial application. We simplify it into three parts which shows in Fig 2. to explain more clearly. Three switches control three parts, named A, B and C. Basically, the factory replaces the medium twice a day. At one hour before replacing the medium, the user needs to turn on switch C to discharge ninety percent of the medium. When it is time to replace the medium, switch C will be turned off and switch B will be turned on to refill medium. When sufficient medium is added, switch B will be turned off and switch A will be turned on to let CO2 in. Just like the animation showed on Fig 1..
Considering the cost, the growth time of our E. coli and the floor area, we optimized replace time of the medium, replace it every twelve hours and with 72 parallel bioreactors. Next, we are going to have more detail description on three parts, which are Gas preparation system and flow system, Medium preparation, and Downstream products purification and biosafety.
A. Gas preparation system and flow system
Fig 3. Diagram of gas preparation system and flow system
According to IGCC (Integrate Gasification Combined Cycle) flow diagram, the fuel is first converted to syngas which is a mixture of H2 and CO. The syngas is then burned in a combined cycle consisting of a gas turbine and a steam turbine with a heat recovery steam generator (HRSG). After CO2 / H2 separation, IGCC can reach the demand of CO2 purity including low SOx and NOx emission fraction of allowable limits of bacteria. Finally, the produced flue gas could enter the pipeline leading to the bioreactor.
In E. coli utilization system, the air is pumped in to neutralize the concentration of CO2. A controlled valve is used to control flow rate and split distribution. When the switch a is turned on, the switch b will be turned off, and vice versa. As for the CO2 inlet and outlet, it will maintain an open system of bioreactor. In other words, CO2 will enter continuously and cause some non-reacted CO2 emitted.
Fig 4. IGCC process flow diagram. Source: Vattenfall. (2010)
Syngas has been treated by sulfur and nitrogen removal, as well as heavy metal removal and cooling tank. Through IGCC process, purified CO2 in flue gas is allowable for E. coli CO2 utilizing.
B. Medium preparation
Fig 5. Diagram of medium preparation
At this stage, we have two sections to consider, medium storage and medium preparation before replacing time.
The medium is composed of M9 salt and xylose. For storage, we will convert it into powder with the required proportion. At one hour before replacing time, pour the powder into the medium tank and turn on the water injection switch. Turn on the stirrer of medium tank to have medium powder and water perfect mixing. The outlet of bioreactor (switch c) will be turned on at the same time, letting ninety percent of the medium in the bioreactor flow out . When the medium have prepared well, turn on the switch a and switch b for replacing medium in bioreactor, while the switch c will be turned off.
We also consider the process of raw materials, especially xylose, which is the key source of our pathway. Since xylose is one of the products of agricultural waste degradation, we visited the 2018 Tainan Biotechnology and Green Energy Expo to consulted with researchers from National Energy Program-Phase II, whose projects was biofuel and biodegradable plastic production via agricultural waste. They had developed technique that degrade cellulose and semi-cellulose by ion solution.
Besides, we have opportunity to collaborate with UESTC-Chian team . They work for degrading straw with synthetic biology and convert the product into bio-fuel. One of the product from straw degradation is xylose. These techniques are eco-friendly and low-energy-require. Therefore, the process development of xylose production will be a low-carbon-emission process.
C. Downstream products purification and biosafety
Fig 6. Diagram of downstream process
We will discharge 90% of the used medium in the bioreactor one hour before new medium flows in. Which means that we let 10% of the culture remain in the bioreactor as seed culture. The effluent medium will be sterilized and filtered in the downstream clean-up tank. At this step, we harvest the bacteria and extracting the by-product such as amino acids, proteins, medicine or bio-fuel. Different extracting process designed depends on different by-product.
Besides, we try to reuse the waste heat of factories for sterilizing. The waste water can be recycled as well through removing toxins and adjusting pH value the effluent could return to the medium tank. As for energy require for this system, renewable energy helps us to reach near -zero carbon emission process.
Furthermore, we would like to set up membrane bioreactor (MBR) system, which use a hollow filter membrane that is able to filter most of bacteria in the sewage sludge. We use the system to concentrate the used medium before extracting by-product. And the water went through the system is able to recycle back to the medium tank.
Fig 7. Picture of waste water recycle system
Fig 8. Picture of MBR from KME technology Inc.
Application : China Steel
Fig 9. Picture of CSC interview
Meeting with experts and stakeholders is important in shaping our project to fulfill the needs of our target user. China Steel Corporation is the largest integrated steel Manufacturer in Taiwan. Also, they had been adopting the algal bio-sequestration by cooperating with the research group at our university.
We were given the opportunity to meet with the senior executive of China Steel Corporation to gain invaluable insight for our research. The meeting commenced with our presentation. During the presentation, we introduced our project, including the bioreactor design and the industrial model. By listing out all the aspects we had considered, we would like to obtain advice on the practical and social considerations involved in the application of our project in industry.
Suggestion and Question
Will the high concentration of CO2 retard growth of engineered bacteria?
Microalgae is reported resistant to SOx and NOx. Does E. coli survive under such conditions?
The two questions above were the main concern of CSC. Basically,the best condition for engineered E. coli to capture CO2 is a lower CO2 concentration without too much SOx and NOx particles. However, we won’t be able to provide an ideal culture condition in Industrial application. After testing the tolerance of E. coli, we conclude that E. coli is possible to survive under that kind of condition in factory and the only effects its expression. It may not capture as much CO2 as culture in the lab.
It is important to define a specific commercial product that can be truly produced since your user may consider its economic viability. They stated that a product that can be widely used is better. At the same time, we should consider current GMO legislation if we want to commercialize those products. The actual condition is not as ideal as in the laboratory, we should optimize the condition to maximize the carbon fixation ability of the microbes.
The record can be separated into two parts. One is about their feedback after interview, another one is our customer investigate questions. We use CSC represent China Steel.
The business model describes how an organization creates, delivers, and captures value in an economic, social, cultural, or other environment. Therefore, we introduce this business model as the basis for assessing the integrity and effectiveness of our ideas to work with our industry and even national research. First, we ask questions about this, and beyond the solution, we also explain why we chose this question. Second, we analyzed future developments, including the advantages of using this approach. Next, we introduce our plan to many relevant departments and discuss with the national research. I hope that this plan can be used to promote this plan in the future.
More and more people are now paying attention to the impact of CO2. The trend of environmental degradation is gradually increasing. Scientist and national worldwide contribute to capture those excessive CO2. However, how to reduce carbon and use it has become a major problem today. Challenges against carbon process are complicate. Except the technique and implement problem, social acceptability and policy are other key factors about carbon process technology.
In general, planting is a method of carbon process, and the current use of green algae as a method of carbon utilization. This year, we hope to combine synthetic biology with the most advanced technologies. We want to draw people's attention to the environment and reuse these environmentally stimulating projects.
Business model analysis
The cost evaluation is always crucial for product being on the market. To compare our engineered E. coli to microalgae, we calculate how much the cost it would be when capturing 1 ton of CO2.
Table 1 Volume required in capturing 1 ton of CO2
|Organisms||CO2-fixation rate (mg/L*hr)||Biomass concentration (gDCW/L)||Specific CO2-fixation rate||Volume requiredd (L)|
|Engineered E. coli||19.6||0.87||22.5||51000|
Fig 6. Different volume required between micralgae and engineered E. coli
For capturing 1kg of CO2 in one hour, 51000 L is required with engineered E. coli carbon utilization. It seems that the difference volume required for utilizing same amount of CO2 is disadvantage of E. coli carbon utilization system. At this situation, we have to look into the design of the different bioreactor. For microalgae culture, it requires a large surface area to increase light intensity. As usual, the height of the microalgae culture pond cannot exceed 0.5 m. In other words, we have to build a 7 m diameter culture pond with the volume of 19000L. In constrast, engineered E. coli is not limited by light. The bioreactor of E. coli can be built with any height in the indoor or outdoor. To scale up the bioreactor, a 5.8 m diameted with 1.9 m height equals to 51000 L which has lower floor area required.
As a result,the bioreactor of engineered E. coli can save more than 30% floor area compared with micoralgae culture pond. Take the floor area of Taiwan as an example, we can build 94 billions of microalgae culture pond to uilize 10% of annual emission with 12 operation hours. However, 1 over 3 of floor area will be save if we replace them with E. coli bioreactor. E. coli bioreactor is more flexible on spacing using, and is less sensitive to weather effect.
The most expensive source in the medium of our engineered E. coli is xylose. 1 mole of xylose will capture 0.17 mole of CO2. Therefore, we need 20.0535 kg of xylose while 1 kg of xylose costs 2 USD. The total cost for our engineered E. coli requires 40.107 USD for capture 1 ton of CO2. In contrast, microalgae needs 1000 liter to capture 250 g of CO2, so it needs 4000 liter (about 4 tons) water while 1 ton costs 9.78 USD. The total cost for microalgae is 39.13 USD.
Table 2 Cost required in capturing 1 ton of CO2
|Item||Microalgae||Engineered E. coli|
|CO2 utilizing rate||250 g/m3/day||19.6 mg/g (DRY cell weight)|
|source required for 1 kg CO2 utilization||4 tons of water||20.0535 kg xylose|
|Cost||39.13 USD||40.107 USD|
|Source||NCKU Annan campus||Adjust reference and experiment|
We take two major industrial in Taiwan for example, which are China Steel Corporation (CSC) and Taiwan Semiconductor Manufacturing Company (TSMC). We had done some research on annual emission and calculated with our CO2 utilization efficiency. We also set the average carbon emission of small and medium enterprise (SME) as a standard goal which was easier to reach. Therefore, we can model the scale of E. coli carbon utilization system working for 1 % CO2 emission of different enterprise.
Table 3 Cost of dealing with 1% amount of industrial CO2 emission
|Industrial||annual emission||1% of CO2 emission per hour||Number of required device||Area required||Operation cost (USD)|
|CSC||3.30 millon tons||3750 kg||4555||11.3875 hectare||150.4 thousands|
|TSMC||0.387 millon tons||442 kg||537||1.34 hectare||17.3 thousands|
|SME||20 thousands tons||23.529 kg||29||0.0713 hectare||1 thousands|
We take two major industrial in Taiwan for example, which are China Steel Corporation (CSC) and Taiwan Semiconductor Manufacturing Company (TSMC). We had research on annual emission and calculate with our CO2 utilization efficiency. Therefore, we can model the scale of E. coli carbon utilization system working for 1 % of industrial CO2 emission.
Our bioreactor applies in the industry, including the magnetic stirrer, pump and controller. It will cost 3313 USD every month if the price of industrial electricity is 0.063 USD per kWh.
Table 4 Energy consumption of different items of device
* hp = horse power
* kW = kilowatt
* kWh = kilowatt per hour in one month
For industrial application design, we focus on manufacturing valuable products using pyruvate and the linkage between our engineered E. coli between factory. We have designed a device containing our recombinant E. coli, constructed a system which links with factory. However, we still look forward to more modifications of our biological pathway and system.
The most important intermediate product, pyruvate, is also possible to be converted to other compounds by E. coli native enzymes or constructed enzymes which is clone into E. coli from other organism. For future work of pyruvate, we expect that it is predicable to produce amino acid, fatty acid, biofuel and even biodegradable plastic. Pyruvate is crucial for central metabolism pathway, the TCA cycle, of most organism and has the potential to become vary biochemistry compounds.
We set our first future goal at producing glutamine, an essential amino acid for human and some animals. We can simply purify it as a nutrient supply. Not only for medical and daily usage for people, but also for animal husbandry. Furthermore, glutamine can easily convert to other amino acid, and potentially produce other proteins.
Fig 10. Diagram of pyruvate in central carbon metabolism
Furthermore, researchers have successfully constructed pathways produced cellulose and Poly 3-Hydroxybutyrate-co-3-Hydroxyvalerate through the TCA cycle. We are confident of manufacturing more valuable and diverse products from pyruvate.
WAs for the device we designed, we expect that it is possible to modify our device for power generator and other industry. Our device can utilize CO2 and convert it into various valuable products. With our system, companies can not only reduce CO2 emission but also make profits.
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