Team:KEYSTONE/Human Practices
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Current Biodegradation Method
In order to help our project to have more understanding about the current issue with rubber pollution, market of rubber and current degrading methods, we interviewed Mr.Hu Houbao as the Member of expert group of China Rubber Industry Association Waste Rubber Comprehensive Utilization Branch and a doctor of Tongji University, via Tengxun meeting. We also interviewed Mr.Qi Xuezhi, as the secretary general of the China Rubber Industry Association’s Comprehensive Utilization Branch, through WeChat call and we asked if they could use their knowledge of rubber to help us to dive deeper into the background information. The information that we’ve learned is listed below:
Interview with Hu Houbao
What are the current ways of rubber degradation?
Through this interview, we learnt that there are three ways of rubber degradation: Prototype utilization, thermal cracking, and recycle rubber powder. Prototype utilization is to recycle the waste rubbers, and reuse it. Thermal cracking is the process how the structure of rubber will break down under high temperature. However, rubber is a polymer material, which is difficult to break down. Recycled rubber power is to ground the recycled rubber from prototype utilization in to powders and use the rubber power in other area. Mr. Hu Houbao also mentioned Refurbishment of rubber. However, according to his answer, this way of degradation is not very common in China.
How is the vulcanization step of thermal cracking achieved?
From Mr.Hu Houbao, we learnt that rubber includes natural and synthetic rubber. The natural rubber has a very small amount of production that is less than 800,000 tons. On the other hand, synthetic rubber come from petroleum after high temperature polymerization. In addition, vulcanization means that the small molecules of rubber were joined together with other chemical additives to produce large molecules. Furthermore, desulphurization is the reversed process of vulcanization. Last but not least, thermal cracking does not involve desulphurization, it is a physical process of changing the rubber’s chemical form and breaks the molecular chain.
Project feasibility and the current market demand for the recycled rubber industry:
To have better understanding about the background, we asked about what are the demands of the current market. According to Mr.Hu Houbao, we learnt there is a strategic importance of the rubber industry, since the independent production in China is 20 to 30% for Petrochemical rubber, and 15% for natural rubber. This shows that rubber industry is not self-sufficient. We also learnt that the current needs of the Chinese rubber market require the recycling system to be 1.) Clean and environmentally friendly, to avoid secondary pollution. 2.) Energy saving 3.) Able to promote recycling
What do you think is the best way to deal with rubber pollution at this stage? How far can current technology accomplish?
Mr.Hu Houbao shared that he believes the current best way to solve rubber pollution needs to balance between economic and environmental values. He gave an example about how waste rubber is a resource rather than pure waste, like how the tires can be remade into renewable fuel and to be utilized as industrial fuel, but there are a lot of pollution in the process of renewing, because rubber has a lot of fillers which contain heavy metals, and can cause a new form of pollution. Like some of the products of thermal cracking cannot be reused, so we need a new method that can cause less pollution.
Conclusion on interview with Mr.Hu houbao:
Here is a summary of the answers we have gotten from Mr.Hu Houbao. The current degradation of rubber will cause pollution because the heavy metals in the fillers of the rubbers, while the current rubber market demand a method that is clean, efficient in terms of energy, and a recyclable method that is environmentally friendly and sustainable.
interviewers from our team and Mr Hu in group chat
Interview with Qi Xuezhi
What are the current ways of rubber degradation?
According to Mr.Qi xuezhi, there are mainly five types of rubber degrading methods currently: Prototype utilization, rubber recycling, thermal cracking, recycling rubber powder and tire retreading. Prototype utilization is to recycle and reuse the waste rubber. The recycling rubber powder method grinds the rubber in to power and makes it into recyclable rubber or asphalt. It has the largest proportion of the overall rubber recycling methods and can be used as a raw material for roads and constructions. Recycling rubber is the next step of recycling rubber powder, it has the production of 70% of the rubber around the world. Thermal cracking uses feverish temperature to crack the tires, and thermal cracking can be used to make cracking gas and crashing oil. The tire retreading method is simply slowing down the waste time of rubber. Mr.Qi Xuezhi told us the most common rubber recycling method in China is recycling rubber powder and recycling rubber. In fact, the production of recycling rubber powder can reach five million tons per year. Thermal cracking is also quite common. It can have the production of four million tons a year. This method is usually used in Jiangsu, Anhui, Zhejiang, Hebei, and Shanxi because there is a rich resource of coal in these provinces.
Project feasibility and the current market demand for the rubber recycling industry:
Mr. Qi Xuezhi told us that in order to evaluate our project’s feasibility in the rubber recycling industry, we need to consider the following aspects:
1.Economic components: the recycle rubber powder has the lowest cost, but for various kinds of rubber, different companies have different demands.
2.Environmental concerns: Tire retreading is a production method for rubber products and therefore has a certain amount of rubber pollution to the environment. Rubber powder has production problems with large machines and copious amounts of electricity. Which will include hazards like dust, noise, and electricity. Recycled rubber needs to go through the process of vulcanization. The rubber in its powdered state is reduced to its chromogenic form, breaking the thiopeptide chain, and this process along with Thermal cracking will produce exhaust gases.
3.Efficiency: the recycling rubber power is the most efficient way of recycling rubber, but it has the lowest profit margin because there are no chemical changes involved, only physical changes. Therefore, the low input leads to the late production base, then to strong competition in market and less profit. Thus, there is less economic profits to be generated.
Are there any regional limitations to these rubber recycling methods?
Through our interview with Mr.Qi xuezhi, we learnt that there are regional limitations in these methods. For example, the three major distribution centers in China dealing with recycled rubber: Shanxi, Hebei, and Zhejiang, where waste tires are gathered there for centralized processing, this is because there’s coal in these regions which can be used as fuel to burn the rubbers. This shows that the limitation of some of the rubber recycling methods are relied on natural resources.
What do you think is the best way to deal with rubber pollution at this stage? How far can the current technology accomplish?
Mr.Qi xuezhi believe that the best way of dealing with rubber’s negative environmental influences of this stage is to deal with the problem of pollution, and especially the pollution during production. This is not a problem of technology, but a problem on the scale of the factories. A factory recycling rubber needs to have a large scare to include rubber degradation method, and the ideal state of a factory is 20-50,000 tons of production per year.
Conclusion on interview with Mr.Qi xuezhi:
Through this interview we learnt that the current ways of rubber degrading method have limitations in region, and it is difficult of a factor to add rubber degradation technology. Because of the pollution in current methods, we need to solve the pollution in rubber degrading and recycling system, while considering the aspects of economy, environment, and efficiency if we want to introduce a new kind of method. Therefore, we decided to choose the biodegradation of rubber as our project.
Project Improvement
Interview with Qi Xuezhi and Hu Houbao
To obtain a comprehensive understanding and diverse perspectives that help enhance our project, we wished to know the technical practicability, environmental impact, market feasibility, and economic impact of waste rubber biodegradation via genetic engineering. As we interviewed Qi Xuezhi and Hu Houbao in the same WeChat conference call, we asked them to offer their perceptions on these aspects.
According to Qi Xuezhi, the precise market practicability of waste rubber biodegradation through genetic engineering cannot be measured. Many mechanisms during this process exceeded his knowledge and the public’s. However, there surely is market potential because various industries consume rubber excessively and need proper waste disposal. Waste rubbers should be decomposed directly, and the products cannot be utilized any further owing to the substantial quantity of various components that not only embodies well-known polyisoprene. Furthermore, rubber decomposition via insects, now available on market, largely resembles our approach, but there is no such systematic, industrialized biodegradation method currently.
On the other hand, Hu Houbao provided another viewpoint on technical feasibility. The high demand of working conditions and insufficient yield of wasted rubber biodegradation byproduct struggle to meet market demand. Limitations within genetic engineering method result in such issue and constrain real-life applications in the market.
Conclusion and improvement:
The market practicability of waste rubber biodegradation via genetic engineering exists despite the uncertainty of its precise extent, while technical feasibility is limited. We should, therefore, ensure that our parts are carefully chosen to enhance the productivity of latex clearing protein and amount of waste rubber decomposed. This is why NusA fusion protein and signal peptide are added to our construction.
Interview with Liu Luo
To verify our general method as well as the parts and processes of waste rubber biodegradation that is used in our product creation, we interviewed Liu Luo, associate professor at College of Life Science and Technology, Beijing University of Chemical Technology, in a Zoom meeting.
Liu first acknowledged our holistic approach, biodegradation. The absence of functional groups makes rubber decomposition difficult than other types of materials like plastics. Traditional rubber consists of polyisoprene whereas the synthesized ones have relatively stable chemical bonds. Traditional method would thus damage the environment significantly, but biodegradation should work better to overcome the challenges of rubber decomposition.
Then, he generally approved the feasibility of our model parts while indicating some existing problems. For instance, bonds that connect monomers in a polyisoprene chain can be broken down by rubber oxygenase. Hydrophobic latex clearing protein works better, and NusA can be applied but must be removed after expression. However, it should be noted that signal peptide must cooperate with in-cytoplasm protein pathway, but since E. coli has no such pathway, the peptide inserted can only secreted in a small quantity, or it just has small number of remainders in the shattered bacteria. Lastly, to examine the spectrum of post-decomposition product, infrared ray can help detect the chemical features of remaining functional group via wavelength.
Conclusion and improvement:
Biodegradation, our general method of rubber decomposition, is properly adopted with feasible applications of rubber oxygenase and NusA. Nevertheless, signal peptide cannont be secreted in a huge quantity due to the absence of protein pathway in E. coli, which results in limited yield of latex clearing protein. Selecting a type of bacteria that triggers substantial quantity of latex cearing protein produced eventually is essential. Bacterial strains of BL21 and C41 were hence utilized since they contain such pathway that enables massive signal peptide secretion.
Our interview photo with Professor Liu Luo
Northern China Meetup Initiated and Hosted by QHFZ_China
To receive preliminary feedback on our project background and design before experiment, we made a presentation to over 60 participants, seven teams on June 20, 2021.
We introduced the global and local issue that drove us to undertake this project, core enzymes involved such as latex clearing protein, and the approaches to refine these enzymes. After our presentation, we obtained expert comments, such as Professor Luo Liu from Beijing University of Chemical Technology who commended our project ideas and approaches provided some constructive input. For example, he indicated that isoprene synthesis, as a well-studied and practiced area, helps achieve a decent result easily but is very difficult to improve or innovate based on earlier studies. After reconsideration, therefore, we removed isoprene synthesis from our design, which was the correct decision because we could focus on a more challenging and essential aspect, cis1,4-polyisoprene decomposition.
THe Northern China Meetup hosted by QHFZ_China
In general, this meet-up was a valuable opportunity to exchange ideas with many other iGEM teams and to acquire knowledge from professional feedback.Plasticase Meetup Initiated and Hosted by CPU_China
To learn various approaches of plastic and rubber decomposition that may refine our product creation, we presented our work in Plasticase meetup that focuses on plastic and rubber biodegradation projects. From over 40 participants and eight teams, we learned diverse methods of plastic and rubber biodegradation, such as cell-surface display, new to our knowledge. It was a great platform to have deep discussions with teams sharing similar outcomes but varied approaches. Valuable understandings were gained as well from student and expert questions and comments.
（Screen shots of the Plasticase Meetup）