Team:RUM-UPRM/Hardware
Our Concept
Stirred Batch Bioreactor System
Figure 1. Diagram of our proposed Stirred Batch Bioreactor System which will permit the biodegradation of RDX using our genetically modified bacteria.
Our proposed bioreactor system for our genetic circuit is a stirred batch type bioreactor. Its main purpose would be to convert raw material into a desired product. In this case our bioreactor would provide the necessary conditions to enable cell proliferation and promote the denitrification of RDX using our bacteria.
Biological water treatment is a biochemical process that is centuries old. Stirred tank bioreactor provides the best conditions for microbial growth and biochemical process to occur. The reactor size, configuration, and mode of operation are key reactor design factors. This reactor will provide favorable physical, biological, and combined physical-chemical conditions for the best biological remediation processes for the pollution of RDX in the Anones Lagoon. A stirred tank bioreactor consists of a cylindrical vessel with a motor-driven central shaft that supports one or more agitators. Stirred tank bioreactors are the predominantly used design for submerged cultures. Stirred tank bioreactors are mechanically agitated, where the stirrers are the main gas-dispersing tools and provide high values of mass transfer rates coupled with excellent mixing.
Advantages of the reactor include:
➜Efficient gas transfer to growing cells
➜Good mixing of the contents
➜Flexible operating conditions
Environments that hold microbial processes are categorized into aerobic and anaerobic. An aerobic environment is characterized by the presence of oxygen while an anaerobic environment completely lacks free oxygen. In the case of the bioreactor we chose to work with, stirred type, it is important to maintain aerobic conditions for the cells to decompose and divide efficiently. Additionally, the production of nitrite is supposed to be higher than formaldehyde production in aerobic environments. Since toxicity levels of formaldehyde are higher than those of nitrite, the fact that formaldehyde will be produced at smaller concentrations/quantities goes along with one of the purposes of our bioreactor process which is to keep toxicity levels as low as possible during decomposition.
Parts
Our proposed bioreactor system for our genetic circuit is a stirred batch type bioreactor. Its main purpose would be to convert raw material into a desired product. In this case our bioreactor would provide the necessary conditions to enable cell proliferation and promote the denitrification of RDX using our bacteria.
Table 1. Parts of our proposed Bioreactor System for the biodegradation of RDX.
| Part | Function and Usage |
|---|---|
| Stirrer Motor and Shaft | These two crucial parts of the bioreactor, the stirrer motor and shaft, work together to ensure the even mixture of the medium. The stirrer motor provides the shaft power to transmit torque to the blades. |
Blades |
|
| Foam | The foam blades, also known as mechanical foam breakers, provide circulation of air in the headspace area of the bioreactor and, consequently, the formation of residual organic matter is prevented. The creation of excess foam during the mixing process is normal but its accumulation may cause handling and pumping difficulties, interfering with the performance of the mixed medium. |
| Impeller | The primary function of the impeller is to continuously, homogeneously mix the contents inside the vessel. Our bioreactor contains pitch-blade impellers, which generate an axial flow and are used commonly for cell culture processes. Additionally from mixing purposes, the impellers also help promote aeration and necessary heat transfer for the process inside the vessel to happen efficiently. |
Vessel |
|
| Container | The bioreactor’s container is an enclosed space that allows the biological reactions to happen effectively, being an isolated controlled environment designed to feed the culture’s needs. Attached to it are the different sensors and inlets used to insert the medium, acid/base supply, steam for sterilization, and air supply. |
| Thermal Jacket | A bioreactor’s thermal jacket is used to control the heat affecting the container. They remove heat exothermic reactions or provide the heat that is needed to produce an efficient endothermic reaction. The thermal jacket contains water that can be heated or cooled and will serve the function of maintaining the container along the correct temperature for the culture media. |
| Sparger | In an aerobic process, a sparger is crucial to provide the culture the air supplies needed. For example, through the sparger, CO₂ addition will occur when pH levels need to be regulated and O₂ will be added according to the value of dissolved oxygen present in the bioreactor. |
Key Parameters |
|
| Temperature Sensor | The temperature sensor reads the precise value of the culture media’s process’s temperature and sends this signal to the temperature control unit. |
| Temperature control unit (TCU) | When abnormal change in temperature is detected in the TCU, the TCU heats or cools water in thermal jacket, bringing the temperature to equilibrium again. |
| pH meter | It is extremely important to have a precise and efficient bioprocess. The pH meter will provide a measurement of the culture media’s pH value and send a signal to the pH control unit. In the beginning of the process, pH is regulated in the range 7.0 ± 1.0. |
| pH control unit (pHCU) | The pHCU is programmed to compare the signal measure provided by the pH meter to the defined target value. The addition of CO₂ or an alternative basic solution will be added if the pH needs to be decreased. In order to increase the pH if needed, air will be added through the sparger in order to move out the added CO₂. |
| Oxygen meter | This sensor monitors the level of dissolved oxygen in the bioreactor and sends the signals to the oxygen control oxygen so it can be effectively regulated. |
| Oxygen control unit (OCU) | The OCU will automatically add O₂ when cells have consumed the oxygen and reached the O₂ target value. When the oxygen level goes below this target value, an automatic addition of O₂ occurs through the bioreactor’s sparger. |
Inlets |
|
| Medium and sterilization steam inlet | In the medium inlet, there is a steam inlet connected to it in order to sterilize the medium before it enters the bioreactor. |
| Acid/base supply inlet | Inlet through which basic solution enters the bioreactor. |
| Cooling water supply inlet | Inlet through which water enters thermal jacket. |
Outlets |
|
| Effluent outlet and sterilization steam inlet | In the effluent outlet, there is a steam inlet connected to it in order to sterilize the medium before it exits the bioreactor. |
| Cold water outlet | Outlet through which water exits thermal jacket. |
Next Steps
Testing Out our Prototype
A small-scale batch bioreactor will be used to test out the treatment of the pollution of RDX. This prototype will bring a conventional water treatment process that employs an aerobic tank, an agitated vessel seeded with bacteria that will enable cell proliferation and promote the denitrification of RDX. Here, suspended growth of the bacteria occurs. Next, the air is sparged from the bottom to provide sufficient dissolved oxygen in the medium. Since the volume of the aerobic tank is usually large, and the solubility of oxygen in water or aqueous solutions is low, air compressors would have to be deployed to sparge in a significant amount of air to meet the oxygen requirement of the bacteria and that of the aerobic process.
This bioreactor will be operated by controlling three different parameter temperatures, oxygenation, and pH. With the agitation creating a homogeneous mixing, these parameters will set the best possible environment to allow cell proliferation and promote the denitrification of RDX concentration in water. Thus, promoting a sustainable prototype to help the community of Vieques, PR, eliminate this hazardous chemical contamination as RDX in their water.
Further Implementation
For future implementation for large-scale bioreactors it is recommended to use a continuous stirred tank bioreactor. In large biological water treatment plants, such bioreactors usually are operated in continuous mode. In a CSTR, the water is uniformly distributed instantly upon entering the reactor. The constant water inlet will allow continued cell proliferation and promote the denitrification of RDX concentration in the water. For more information regarding our proposed implementation plans, check out our Implementation page.
References
Asenjo, J. A. (1994). Bioreactor system design. CRC Press.
Reinhart, D. R., & Townsend, T. G. (2018). Landfill bioreactor design and operation. Routledge.
Van't Riet, K., & Tramper, J. (1991). Basic bioreactor design. CRC press.
Zoh, K. D., & Stenstrom, M. K. (2002). Application of a membrane bioreactor for treating explosives process wastewater. Water research, 36(4), 1018-1024.