Abstract
Our product is mainly designed to use shrimp shells as raw materials to cultivate Clostridium tyrobutyricum (C. tyrobutyricum) to independently produce butyl butyrate as a biofuel. The space industry and factories with huge energy consumption are our potential end users. To use our product to produce the biofuel butyl butyrate, three steps are required: decomposing shrimp shells, culturing our engineered C. tyrobutyricum with the N elements as nutrients in decomposed shells together with our engineered E. coli, extracting and storing butyl butyrate. We designed a crushing and drying machine to efficiently decompose shrimp shells into dry powders and a storage tank to safely store the fuel. Proper handling of the two devices are needed for safety concerns.
1. End Users
Through early stage HP work, we interviewed several experts to clear our ideas about kitchen wast pretreatment and collection. We learned from Prof. Lv, that to achieve economic strategy for biofuel production, raw materials including crab/lobster shells, common straw containing rich lignin and animal waste can used. These sources have great potential as substrates for cheap bioenergy manufacturing. Prof. Tian also suggested us to recycle the waste by using it as fertilizer to reach the economic cycle. Therefore, our product is mainly designed to use shrimp shells as raw materials to cultivateC.tyrobutyricumto independently produce butyl butyrate as a biofuel.
Our products are mainly produced by using shrimp shells as raw materials to cultivate Clostridium tyrobutyricum (C. tyrobutyricum) to independently produce butyl butyrate as a biofuel. Through the previous research, we learned that the space industry and factories can be our potential users. The interest in using biofuels in aviation gas turbine engines is relatively new. Compared to ethanol, n-butanol has some better fuel properties, such as higher energy density, less hygroscopicity, lower vapor pressure, higher flash point. Butyl butyrate is another potential candidate that could meet the chemical performance requirements of alternative aviation fuels. Butyl butyrate has similar physical and chemical properties to aviation diesel at low temperature and can be directly used as aviation fuel. It has a high octane rating of 97.3 with excellent compatibility and properties as gasoline, aviation kerosene and diesel components. Compared with other traditional methods for producing butanol fuels, the cost of biosynthesis of high-yield butyl butyrate by C. tyrobutyricum is much lower. Therefore, the space industry would be our main users for the product, such as SpaceX, Rocket Lab and so on.
2. Product operation
To use our product to produce the biofuel butyl butyrate, three steps are required: decomposing shrimp shells, culturing our engineered C. tyrobutyricum with the N elements as nutrients in decomposed shells together with our engineered E. coli, extracting and storing butyl butyrate.
We designed two devices to be used in two of the above steps for biofuel production:
Step 1: Crushing and drying shells
By exploring the structures of wall breaker machines and dryers, we designed a crushing and drying machine for the shrimp shell decomposing. To use the machine in general, the user adds the shrimp shells and water into the machine, closes the lid, switches on the crushing button, pours out wasted water halfway, finishes the crushing, turns on the drying button, waits and collects the final dry powder when it is done. Operators for our product do not need specific expertise, though a short-term training and familiarity with safety matters is required. In order to prevent personnel from using the machine incorrectly and causing accidents, the equipment used at each step needs to be equipped with operating instructions. Operators need to especially pay attention to the safety while in the operation of the high-speed rotating blades to decompose shrimp shells.
Figure 1 Illustration of our crushing and drying machine
Step 2: Fermentation of C. tyrobutyricum and E. coli
By searching industrial-scale fermentation, we found that there are many commercialized facilities for bacteria culturing (Figure 2). Therefore, the coculturing of the engineered C.tyrobutyricum and E.coli can be done utilizing commercially available fermenters. The culturing material should include shrimp shell powder and material rich in nitrogen. The fermentation process should abide by the corresponding industrial standards.
In terms of extracting efficiency of biofuel, we learned from an expert in the field, Mr. Xin, that we could use the lipase surface display, which could avoid subsequent product extraction steps, to reduce costs and improve the application value. However, in order to avoid by-product generation, we chose to improve the way of extracting the lipase. The lipase used in the synthesis is prepared by the fermentation of our engineered E. coli and extracted by a chitin binding site, which allows us to acquire lipase with high purity and vitality. Extraction of butyl butyrate from the fermenters can be achieved by conventional organic compound extraction methods.
Figure 2 Large-scale fermenters (Hwaegemn bbepp, via Wikimedia Commons)
Step 3: Storage
After investigating the existing chemical storage methods on the market, we combined the simplest and most effective storage tank form, and added adjustment of the observation window to ordinary storage tanks. A current storage tank has an observation window, but the window is often rectangular with limited viewing angle and does not have a sun visor. We designed a circular viewing window to expand the observable area of the liquid in the tank and added a sun visor to effectively avoid deterioration of the liquid behind the window by direct sunlight. In addition, commonly used horizontal storage tanks occupy large space and many factories have limited warehouse. Our storage tanks have an angle adjustment design, so that they can be placed horizontally or vertically. Vertical position can be used when storage space is small. The stability is better in horizontal position. Operators need to be careful when adjusting the angle snap to avoid high-weight storage tanks hitting pedestrians.
Figure 3 Illustration of rotation and fixation of the storage tank
3. Real-world implementation
In real-world application, production yield is a key factor for economic and practical aims. We consulted experts in related fields for inspirations to improve the yield and lower cost for our product. Prof. Wang inspired us to mitigate by-product production by adjusting the molar ratio of butyric acid and butanol to 1:1. According to her advice, we conducted our mathematics model using the genome-scale mode (GSM) of C. tyrobutyricum to investigate the key factors of balancing butanol and butyric acid production which gave us a guidance for future improvement.
Our products may be affected by the following factors in real world.
After referring to IGCSE economics, and business textbooks, we came to the solution for improper usage of the devices：fix the training time of the operator for 1-2 months, and have experienced personnel to assist the operation for a week so the operator can be familiarized with the operation to avoid accidents. Operators need to check connection of components before using the machine. The blade should be inspected regularly for hard residues, damages, and etc, and should be replaced when necessary. For the storage tank, the lid is not connected to the body, and the valve needs to be closed manually after each addition of liquid, so the lid is easy to lose.
4. Safety
After consulting Professor Fengxue Xin, we learned that C.tyrobutyricum is a probiotic and not a pathogen, so there is no major safety problem in the operation process. At the same time, we use a closed fermentation system, which will be sterilized later, and will not escape into nature or cause gene leakage, so there are no ethical issues. The normal sterilization process of biological laboratory is routine biological sterilization in high temperature and high pressure environment.
For shredding shrimp shells, maintenance personnel should check the machine every month to ensure the blade is not damaged, and there is no residual shell stuck to prevent motor burn out and safety issues. Improper operation can endanger operators due to high speed rotating blade. Operators need to operate the instrument in strict accordance with the instructions after about 2 months of safety training.
Butyl butyrate mildly irritates eyes and skin and is a marine pollutant, so it should be handled with care during production, transportation and disposal. All storage tanks should be firmly fixed. Maintenance personnel can be set up to check the tanks every month to ensure that the tank gate can be tightly closed and the tank body is not rusty. The angle adjustment buckle of the tank can only be adjusted by 90° and is a pull-out design. If operated improperly, the tank might be unstable and tilt with high acceleration due to its weight. Operators need to strictly follow the instructions after 2 months of safety training to avoid such incidences.
5. Challenges and prospect
The future challenges we may face include better future substitutes for the biofuel butyl butyrate, as there must be more efficient fuels that have not yet been found. The separation of raw materials from shrimp shells is another problem. Large amounts of resources are consumed in collecting and classifying the waste, and advising people to separate shrimp shells from their daily garbage and offering them to the lab is hard work unless the people who do it are rewarded. Also, for the public to accept a new type of fuel demands time and proper public activities. Great efforts and professional help are needed to promote the new biofuel. As suggested by Prof. Lv during our interview, cooperating with the related departments or governments for collecting wastes may be an efficient way to solve the problem.
During the HP work, Prof. Tian helped us figure out suitable method of pretreatment of shrimp and crab shells waste for the later production of biofuel, such as oil-water separation, deodorization, and fermentation of phosphorous and nitrogen. In this early stage of development, we designed the crushing and drying machine to treat the shells. In the future, more measures can be designed to pretreat the kitchen waste more properly so that the production of biofuel can be more efficient. As for the crushing and drying machine, more energy-saving and effective shredder may be available to complete the work.
For the storage tank, its snap design only allows the adjustment of two angles, more advanced angle adjustment design that can be automated rather than manually operated may appear in the future.
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