Product Design

1. Overview

The emission of carbon dioxide (CO₂ for better understanding) is a serious problem the world has faced for a century. Although existing methods can reduce carbon dioxide, it still can't load massive emission of CO₂ from the industry. Thus, our team uses E. coli to capture CO₂, providing another choice in excessive CO₂ emission problems.

In addition, we trace back to the CO₂ emission source. Factories are the main field to produce large amounts of CO₂, so we designed a complete factory flow chart. We received lots of suggestions provided by industry, professors and experts in different specialties. After considering all cost advantages, we have built a device which has commercial specifications.

2. Flow chart


There are many aspects we need to consider. First, we consider the emission velocity of carbon dioxide from the factory, the medium exchange rate and the growth time of our E. coli. We design a process. The factory needs to replace the medium twice a day, so 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 carbon dioxide in.

In order to reduce the cost, on the growth time of our E. coli and floor area, we decided to replace the medium every twelve hours and use 72 parallel bioreactors.

3. Detailed description

A. Gas preparation system and flow system



According to IGCC flow chart, the gas has been treated by sulfur and nitrogen removal and then enters the pipeline leading to the bioreactor. Use pump to enter air to neutralize the concentration of carbon dioxide. Control flow rate and split distribution with controlled valve. When the switch a turn on, the switch b will turn off, and vice versa. The carbon dioxide inlet and outlet will still open.

B. Medium preparation



At this stage we will match the proportion of m9 salt and xylose and change it into powder. At one hour before replacing the medium, pour the powder into the medium box and turn on the water injection switch. The medium box will use a stirrer to stir and at the same time the outlet of bioreactor (switch c) will turn on to let ninety percent of the medium in the bioreactor flow out. When it is time to replace medium, turn on the switch a and switch b, at the same time, the switch c will be turned off.

C. Downstream products purification and biosafety



We will dispose 30% of the used medium in the bioreactor one hour before new medium flows in. Which means we let 30% of the used bacteria remain in the bioreactor. We designed this system to maintain a steady amount of bacteria in our bioreactor. The used medium will be sterilized and filtered in the downstream clean-up tank. At this step, we can harvest the bacteria by centrifuging and extracting the terminal product such as amino acids, proteins, medicine or bio-fuel. The expect the heat for sterilizing is from the waste heat of factories, the waste water can be recycled after removing toxins, and adjusting pH value and the energy the device require is green energy.

China Steel

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.

Process

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 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.

Cost Evaluation

Volume

Cost

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 1000 kilograms CO₂. The most expensive source in the medium of our engineered E. coli is xylose. 1 mole xylose will capture 0.17 mole CO₂, so it would need 20.0535 kilograms xylose and 1 kilogram xylose is cost 2 USD. The total cost for our engineered E. coli is require 40.107 USD for capture 1 kilogram CO₂. In contrast, microalgae need 1000 liter to capture 250 gram CO₂, so it need 4000 liter (about 4 Tons) water and 1 tons is cost 9.78 USD (300NT). The total cost for microalgae is require 39.13 USD.

Future Work

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.

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.

Reference

1. Fuyu G, Guoxia L, Xiaoyun Z, Jie Z, Zhen C and Yin L. Quantitative analysis of an engineered CO2-fixing Escherichia coli reveals great potential of heterotrophic CO2 fixation. Gong et al. Biotechnology for Biofuels, 2015, 8:86.
2. 張嘉修、陳俊延、林志生、楊勝仲、周德珍、郭子禎、顏宏偉、李澤民 (2015), 二氧化碳再利用─微藻養殖, 科學發展　2015 年 6 月│ 510 期