Introduction
In our pursuit to apply our engineered bacteria in diverse settings, including family homes and factory facilities, we encountered a critical need for specialized bacteria cultivation devices. However, the existing bacterial culture and deodorization devices proved insufficient for the demands of our new approach. Consequently, after multiple rounds of research, design, construction, testing, and learning(Figure 1) (more details in engineering page), we finally designed a dedicated and innovative hardware solution. This device enables our engineered bacteria to effectively remove formaldehyde while preventing any adverse environmental impact.
Design
In our hardware, contaminated air containing formaldehyde is pumped into the primary fermentation tank under a constant pressure by the air compressor. As the room's air passes through the initial air filter, airborne bacteria are entirely removed, resulting in sterile air entering the fermentation tank. Within the fermentation tank, the engineered bacteria interact with the contaminated air. The engineered bacteria metabolize the formaldehyde in the air, converting it into carbon dioxide. This process efficiently eradicates the harmful formaldehyde, and ultimately, the purified air is released.
However, as the air passes through the culture medium containing engineered bacteria, there is a potential for the engineered bacteria to escape into the expelled gas. To mitigate this risk of engineered bacteria leakage, we have incorporated an additional air filter at the exhaust outlet of the fermentation tank. This precaution ensures that the purified air remains free from any engineered bacteria contamination.
Additionally, to prevent the dissemination of odors originating from the engineered bacterial culture solution indoors, we have incorporated a highly efficient activated carbon odor filter immediately downstream of the exhaust air filter. This arrangement guarantees that the discharged air is entirely free from any odors.
Finally, we also added an exhaust pipe similar to a goose neck bottle to prevent bacterial contamination at the outlet.
Components
Overview
Our hardware comprises the following components: a fermentation tank, two air filter, an activated carbon odor filter, an air compressor, ventilation pipes, and an anti-pollution exhaust pipe(Figure 3). Main components of the equipment are constructed using 304 stainless steels. The entire system is fully sealed, except for the ventilation and exhaust devices.
Fermentation Tank
We have innovatively designed a fermentation tank with a distinct structure(Figure 4). In this tank, to ensure a secure connection with the filtration system, we have incorporated external chuck components on both sides of the fermentation tank cover for sealing and connectivity purposes. Additionally, to guarantee even mixing of the engineered bacteria within the tank during ventilation, we have extended the ventilation port located on one side to reach the center of the tank bottom.
Furthermore, recognizing varying requirements, we have designed fermentation tanks of different sizes, with diameters ranging from 20 centimeters to 50 centimeters. These diverse tank sizes cater to the specific needs of indoor spaces, accommodating varying formaldehyde levels and room sizes, thus ensuring effective formaldehyde removal.
Air Filter
To maintain sterility both when introducing air into the fermentation tank and when releasing gas from it to prevent any contamination of the engineered bacterial culture medium, we have implemented a specific solution. At each inlet and outlet, we have incorporated small 2.5-inch air filters with dimensions measuring 17 centimeters in height and 7.6 centimeters in width (Figure 5). These filters utilize polypropylene microporous membrane filter elements with a filtration accuracy range from 0.1 micron to 0.5 microns, effectively preventing contamination of the engineered bacterial culture medium.
These air filters have a maximum working temperature of 120°C (at 0.28 MPa), a maximum positive pressure difference of 0.42 MPa (at 25°C), and a maximum back pressure difference of 0.28 MPa (at 25°C). They are characterized by their low-pressure difference, high flow flux, long service life, stable performance, and wide chemical compatibility.
Figure 5. Air filter and filter element
Odor Filter
After passing through the fermentation tank device, harmful formaldehyde in the air is removed. However, any odors from the culture medium may potentially enter the indoor environment with the expelled gas. Therefore, following the air filter at the exhaust outlet, we have added a 5-inch odor filter, measuring 26 centimeters in height and 10 centimeters in width (Figure 6). The odor filter consists of a housing, 100-mesh screen, and activated carbon.
To ensure the device's sealing, we have chosen a screen filter housing to contain the activated carbon. An ample amount of activated carbon is placed within the 100-mesh screen, which is attached inverted to the outlet air filter. The purified and sterilized air from the air filter is further passed through the odor filter to eliminate any unwanted odors, ultimately releasing purified and odorless gas.
Air Compressor
We have opted for a pressure-adjustable air compressor with a 30 L air tank capacity and a discharge rate of 30 L/min for pumping contaminated air into the fermenter (Figure 7). To maintain stable pressure during the introduction of contaminated air and prevent it from becoming excessively high or low, we've equipped the air compressor with a dual electric valve device. This system halts the air compressor when the pressure is too high and restarts it when the pressure is too low.
Additionally, to mitigate noise levels and ensure that the entire device operates quietly, we have opted for a silent air compressor.
Exhaust Pipe
We designed our unique exhaust pipe, taking inspiration from Pasteur's gooseneck bottle design (Figure 8). The exhaust tube follows a diagonal downward path, making two bends before terminating in a vertical downward direction. This configuration efficiently directs external bacteria from the air outlet into the odor filter without disrupting the smooth flow of gas discharge.
Connectors
To achieve a robust and airtight seal within our device, we employed a chuck with a 5.05 cm diameter as the interface between various components. Additionally, a silicone gasket was strategically placed between these two chucks to enhance the seal (Figure 9). The sealing process involved the use of a medium-sized chuck clamp, tailored to fit the 5.05 cm chuck. For the connection of the air tubes, we opted for Φ8 type air tube connections, which were effectively sealed with the ventilation tube (Figure 9).
Figure 9. Connectors
Temperature Controller
The ideal growth temperature for our engineered bacteria is approximately 37°C, facilitating efficient formaldehyde metabolism. Accordingly, we have integrated temperature control heating pads into the device, which ensures that the entire system consistently maintains the optimal temperature.
Costs
Prices of Components
We have chosen to use 304 stainless steels in the construction of our devices due to its exceptional durability stemming from its high strength. As a result, our devices boast an extended service life of over 10 years. Maintenance primarily involves an annual replacement of the filter cartridge, air compressor vent tube, and activated carbon to ensure the unit's continued optimal performance. This maintenance routine contributes to the overall cost-effectiveness of our devices.
Applications
During device operation, we take the necessary steps for sterilization beforehand and inoculate engineered bacteria into the culture solution within the tank. When necessary, we retrieve the device, conduct cleaning procedures, replace the culture solution, and re-inoculate it with engineered bacteria as needed. This design ensures that users of our device are not required to perform any manual operations, making it exceptionally convenient to remove formaldehyde from homes and various other settings by simply connecting the device to an air compressor.
Furthermore, we have thoughtfully designed devices with different volumes to accommodate various application scenarios and usage patterns. This approach enhances the versatility of our solution, catering to a wide range of needs.