Team:SDSZ China/pf

iGem SDSZ_China 2018

Product flow

1.over view

The automatic machine we designed is composed of six units. To successfully obtain industry applicable chitosan from lobster shells, the first basic part of the processing system is designed to be the purification of chitin from highly crystalized shells. We have invented five processing units that are assembled to achieve this goal. The steps are the pretreatment of raw materials, the reaction with sodium hydroxide to remove protein, rinsing, and eliminating minerals. After obtaining purified chitin, the most crucial step comes to the transformation process from chitin to chitosan through a specially designed container filled with effective enzymes that we synthesized.

2.The Procedures involved

1). The Pretreatment of materials


Large scale of industrial production requires storage system of raw materials that ensures both the stable quality of reactants and the convenient applicability of them for further treatments.
In our design, the first unit of the machine functions to eliminate physical impurities mixed in the raw materials and as a container of the treated materials.
The storing compartment mentioned above is installed with an electric fan, heating device and a discharge gate.
When the raw materials are placed on top of a filter screen and put into the container, sodium hydroxide inside would actively react with the impurities and rinse them off the lobster shells. These impurities can be brought away and discarded through the discharge gate, leaving the roughly purified lobster shells inside the compartment above the filter screen, which can be lifted and transferred to the second reaction tank of the mechanical system.

Thus, the pretreatment and storage of raw materials can be achieved through rinsing in alkali and constant drying. The automatic design greatly eliminates the need of operators involved in the process, and thus reduces the possibility of the occurrence of safety accidents on laborers.

2). Remove protein.


In order to obtain highly purified chitin from crystalized lobster shells, it is necessary to remove the protein inside the shells, which can ensure high efficiency of transformation from chitin to chitosan. We have designed a set of biological reaction tanks to allow the reaction take place efficiently in the most time and energy saving method.

Reaction Theory

The whole process of the reaction takes place inside three adjacent reaction tanks A, B, and C. According to experiment data and relevant scientific journals, the removal of protein inside crabs and lobsters’ shells requires continuous reaction with alkali. It is documented that the alkali solution needs to be replaced after a 24-hour reaction to ensure producibility and efficiency, after which the lobster shells still need to be in contact with newly added solution for complete 12 hours without heating or 4 hours with heating to undergo the complete removal of protein. It is applied in industrial production that the solid sediment abstracted from the remains of the reaction can be used as fertilizers, while the liquid supernatant of the deposited reaction system can be reused for another round of reaction with lobster shells. By analyzing and synthesizing useful information, we gained inspiration and successfully designed a new reaction system that significantly reduces total reaction time and better utilizes the reaction tanks as well as the reactants.

Mechanical Design

As shown in the figure above, the reaction tank is composed of chamber A, B, and C in which lobster shells can fully get in contact with sodium hydroxide solution. All chambers are equipped with timers and transport units while one of the chambers is equipped with a heater.
A specially designed time regulation design shown in the graph below ensures that each chamber has the least amount of time staying unoccupied, and thus improving the reaction efficiency and saving energy, since only chamber B needs to be heated throughout the complete round of reaction. The traditional time for one fixed amount of materials to transform completely is seventy-two hours per unit while using our new plan, we simply need fifty-four hours per unit and can increase the efficiency by 33%.

After filling all of the chambers with low concentrated alkali solution, the reaction cycle starts. When one round of 24-hour reaction is completed inside chamber A or C, the lobster shells are abstracted from the chamber and put into chamber B through the control of timers and transport units. The materials react inside chamber B for a heated reaction of 4 hours or a non-heated reaction for 12 hours. The leftover of the reaction inside chamber A and C are provided time to fully deposit, and the sediments are extracted after a 12-hour deposition as chemical fertilizer while the liquid supernatant remains inside the tanks to react with a new round of lobster shells. Meanwhile, when the transformation inside chamber B is finished, the products of the reaction are abstracted and transferred into the next unit of the machine while the leftover of the reaction keeps on depositing for 8 or 12 hours (depending on if the former reaction is heated) until solid sediment can be fully set apart and abstracted from the liquid supernatant.


The calculated and specially designed time control system of the reaction indicates higher efficiency of the reaction by increasing the utilization of each reaction tank in a given amount of time. The deposition of reactants not only increases the utility of all products and by-products of the reaction, but also helps reduce the overuse and emission of alkali solution. The process protects natural water body. Energy consumption is decreased in that only one of the three tanks needs to be heated discontinuously during the complete process of the reaction, and the amount of safety accidents caused by wrong operation while heating is consequently reduced to the least.


After crystalized lobster shells are finished with the reaction with alkali and are removed of protein, the products are put into a container that is filled with water for rinsing. A pipe derived from a diluted water tank connects to the container. The leftover protein substances sticking on the shells could be rinsed off during the process and the liquid waste can be emitted from a discharge gate at the bottom of the container. A transport device on the container takes the rinsed products to the next reaction tank.

4). Eliminate minerals


To further purify and completely abstract chitin from crystalized lobster shells, another step of treatment is necessary for the completion of the process, which is the removal of minerals (especially calcium) inside the shells.

Reaction theory

We decided to use hydrogen chloride to dissolve and remove the calcium inside the shells and adopted the similar design of how we treat the materials with alkali. Since there are no specific criteria in market on the use of acid in chitosan production, we used the exoskeleton of lobsters to experiment and found out that acid with the concentration of 5mol/L is the most effective dose in industry conversion.

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Mechanical Design

Considering that the removal of minerals also requires the renewal of acid solution during the complete reaction, we adopted our mechanical design of the materials’ reaction with alkali.
Reaction tanks A, B, and C are adjacent to each other and are equipped with transport units. Reaction tank C is insulated with the surroundings and equipped with gas sensor.
The materials are put into reaction tank A for primary reaction with hydrogen chloride and transported to reaction tank B to react with renewed solution. After certain period of time controlled by the timer, the products are transferred into reaction tank C for detection. The final products are transferred away for rinsing after there is no more gases emitted from the reaction.


The use of low concentrated acid during the production decreases the contamination level of liquid waste to the environment and reduces safety accidents during the transformation.
The design of the detection tank ensures the completion of the reaction and saves time during the production.



Up to this step, the purification of crystalized chitin from lobster shells is completed through the steps of the pretreatment of materials, reaction with alkali solution, rinsing and removing minerals. However, all of these steps are only preparations for the last and the most crucial step of the whole reaction system: transformation. Applying biologic method of transformation to chitosan’s industrial production demands specially designed mechanical device that controls not only the release time of engineered E. coli cells but also the complete reaction process and further purification treatments of final products.

Mechanical design


The container of the reaction is composed of three layers, with the first layer filled with LB culture, the second layer divided into four chambers, each of which filled with engineered E. coli cells and the lowest layer placed with purified chitin transported from the former reaction tanks. At the bottom of each layers are discharge openings, and four timers are implemented on the walls of the second layer to control the releasing time of cultured bacteria. An ultrasonic cell disruptor is attached to the second layer of the container and a centrifugal machine is connected with the third layer of the container. The centrifugal machine is responsible to centrifuge crude chitosan obtained from the catalyzation of enzymes and centrifuge the adherent protein from the bacteria leftover and LB culture. A container is connected to the centrifugal machine with transport device to store the purified products, and a drying unit is attached to the container to dry the products for long-time and stable storage.

Reaction Theory

The catalyzation and decomposition functions of enzymes require suitable environment and time to realize, which makes the design and control of the releasing time as well as the culture of bacteria especially crucial in the complete reaction system. We aim to be efficient, time saving and as economic as possible during the automatic process of transformation, and thus have designed the reaction tanks with the belief that the mechanical design should not only be applicable in industry, easy to operate but also energy and time saving. When LB culture is released into the middle layer of the container, timers on the tanks would begin recording and half of the bacteria in each segment of the second layer is released to the ultrasonic cell disruptor when they reach the stagnate phase of cell growth, as the most abundant protein are expressed. This can be achieved with reference to the data from previous experiments on the measurement of the curve of E. coli’s cell growth and through the control of timers on the reaction tanks. What needs to be stressed here is that the second layer of the reaction tank is divided into four segments and each segment has an individual discharge opening that allows the bacteria into the third layer. The design allows the purified chitin at the bottom level to be always reacting with enzymes since LB is released to different segments with time difference, and thus the bacteria reach the stagnant cell growth period at different moments. After the cells are completely disrupted, the enzymes that are released from the cells are transported to the lowest level of the former reaction tank to get in contact with purified chitin and start to react actively. The final products from the reaction would undergo one last step of treatment which is the further purification through centrifuge and are then abstracted and collected for storage.

3.Improvements upon traditional method

1) Efficiency
Through the design of reactors and time-control systems, the efficiency of production is greatly enhanced. Through numerous experiments in the lab, we found out that there is no need to grind the lobster shells during the pretreatment process, for the reaction can take place spontaneously without the shells being grinded, and thus reducing the time needed to treat the materials aforehand.
The design of the linked reaction tanks for the removal of protein and minerals reduces the time that each compartment stays unoccupied, and thus improves the efficiency in a great deal. The traditional time for one fixed amount of materials to transform completely is seventy-two hours per unit while using our new plan, we simply need fifty-four hours per unit and increase the efficiency by 33%.

2) Energy Consumption
Since none of our designed reaction tanks are unoccupied individually for long period of time and the linked reaction tanks work as integrated systems, the consumption of energy is conspicuously decreased during the complete process.
The only step of our reaction through the processing of the machine that requires heating takes place when treating the materials with alkali. Energy usage is reduced in that only one of the three tanks needs to be heated discontinuously during the complete process of the reaction, and it only takes 2% of the total amount of time.

3) Safety
Our initial purpose of designing the machine was to solve the existing problems of industrial production, which include high level of safety risks. The redesigned flow of production greatly reduces the possibilities of occurring safety accidents in that we adopted low concentrated alkali and acid while dealing with the reactions.
Since there are no specific criteria in market on the use of acid in chitosan production, we used the exoskeleton of lobsters to experiment and found out that acid with the concentration of 5mol/L is the most effective dose in industry conversion. Though the data does not seem a grand difference, usually the concentration of hydrochloric acid in industrial production is 30%, which can cause corrosion and seriously harm human bodies while in contact.

4) Labor demand
The automatic machine requires fewer laborers during the production and thus reduces the cost for factory owners. We have noted that not grinding the shells in the first unit of the machine does not affect the efficiency of the production. As a result, we completely deleted this step which used to demand large involvement of laborers and artificial operation. What is more, all of our devices are equipped with timers, sensors or transporting devices that shape the reaction tanks together as a system, through which automatic processing is consequently achieved.

5) Waste Treatment
One of the most significant advantages of using biologic method to treat chitin is that it causes no water pollution. The only by product of enzyme catalysis is acetic acid which is dissolvable and causes trivial pollution to natural environment if released without treated.
What is more, all of the liquid waste of the reactions is collected and treated for release to the environment, being more environmentally friendly than the release of chemical concentrated solution caused by the chemical production of chitosan.