DESIGN SOLUTIONS

Lab Adaptable Bioreactor:

Figure 3. ACAD design of our LAB.

PHYSICAL DESIGN

To produce accurate models and projections for our Field Adaptable Bioreactor, we will need accurate data. At the same time, we need our Lab Adaptable Bioreactor to resemble conditions in the field, and therefore it should be of relatively similar scale. Given our initial estimations, a 40L bucket should be able to produce enough yeast for a small group of people and therefore would suffice. Removing as much yeast with as little water possible was a significant challenge to overcome, since yeast is a single-celled fungus ranging between 5-10 μm in diameter. Centrifugal separation would either be too complicated a design or leave us with too much water, and typical micron filters would get clogged and become quickly ineffective. To solve this dilemma, we found a stainless steel, 1-micron, 4-layer mesh filter that won’t clog as easily and can be cleaned in an autoclave.

ELECTRICAL DESIGN

The most pertinent data for us is the growth conditions against diffused oxygenation levels, pH, temperature, the corresponding growth rates, settling rates and anything else that may require design considerations.

To achieve this we have the Gravity: Analog Dissolved Oxygen Sensor for determining the oxygenation rates in the solution because the yeast is an obligate aerobe meaning it requires oxygen to grow. Literature has shown substantial growth with 9L/min of air being pumped into the solution and therefore we are using a commercial air pump for aquariums that is capable of delivering a maximum 50L/min of air (Braga, 2015, 55-62). From that, we will be able to determine the minimal amount of oxygenation needed for growth and find a range of values to be able to predict the growth for that specific range.

To monitor pH, we are using the Gravity: Analog pH Meter Pro. This way we can continuously monitor the pH as it might change with cellular respiration. Our concern is that the yeast will convert the oxygen into CO2 and that CO2 in the solution will lower the pH to a point where the yeast will no longer be able to sustain life. Fortunately, our yeast can thrive at a pH of 4.5. (Timoumi, 2016)

In order to maintain or simulate the temperatures or temperature fluctuations of the locations we intend on distributing our yeast, the bioreactor will have an aquarium heating element and a DS18B20 digital thermometer.

Each of the components are controlled with an Arduino inside a 3D printed box with all of the data being saved to the Geekstory micro SD module as comma separated values in a text file. This text file can then be used to create a graph using generated data. In addition, a DS3231 time module will timestamp the data to ensure an accurate interpretation of the data.

You can find the code on the github here: Lab Adaptable Bioreactor Source Code

SAFETY

Since some of the electrical components are using an AC current, safety is a major concern. To address these concerns, we made sure to include the following:
-Wire joints are sealed and hidden underneath the components
-Use of 16AWG wire
-15 Amp Fuse
-The bioreactor is grounded in case the heating element fails

Field Adaptable Bioreactor:

The general design for a Field Adaptable Bioreactor includes two tanks; one tank will act as the main culturing tank and the second tank will be the collection tank. Once the main tank has reached the desired levels of yeast production, users will drain 75% of the yeast solution into the lower collection tank. In the collection tank, the yeast will have time to settle to the bottom. A drain located just above the height of the settled yeast can then drain most of the water leaving the yeast behind. To minimize the modifications and parts required, a simple siphon can be constructed. The remaining water could then be evaporated by placing a fire under the collection tank, making the yeast easier to collect, store and consume. The fire would also be used to sanitize the collection tank to ensure nothing harmful begins to culture.