Product Design

Fig.1 Flow chart of E. coli carbon utilization system

1. Overview

The emission of carbon dioxide (CO₂) 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. Control System


Fig. 2 Overview of the control system

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. From Fig. 1 and Fig. 2, there will be three parts in E. coli carbon utilization system. Three switches control three parts, named A, B and C. Basically, the factory needs to replace 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.

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. 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 chart, the syngas has been treated by sulfur and nitrogen removal, as well as heavy metal removal and cooling tank. Then it produces flue gas that enters the pipeline leading to the bioreactor. Besides, we pump the air to neutralize the concentration of CO₂. Control flow rate and split distribution with controlled valve. 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 enters continuously and there will still cause some non-reacted CO₂ emitted.

B. Medium preparation



Fig. 4 Diagram of 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



Fig. 5 Diagram of downstream process

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.

Entrepreneurship : China Steel

Fig.6 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. Click here to know more in Entrepreneurship：Process, Suggestion and question and Interview record.

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.

Interview record

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.

Cost Evaluation

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.

Table 1 Volume require in capturing 1000 kg CO₂

Volume

Cost

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.

Table 1 Volume require in capturing 1000 kg CO₂

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.

Fig. 7 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.

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
3. Lawrence Irlam (2017), GLOBAL COSTS OF CARBON CAPTURE AND STORAGE, Global CCS Institute, Senior Adviser Policy & Economics, Asia-Pacific Region