We developed a closed bioreactor system and implemented online monitoring system which can live monitoring several environmental parameters. Here is the detail of our bioreactor.

Gas inlet port are located on the bioreactor’s lower part while outlet port are located on the bioreactor’s upper lid. As low concentration CO2 enters the bioreactor, it flows through the diffuser refiner and dissolves in the buffered medium to form acid. A pH sensor and temperature sensor is installed to monitor the bioreactor tank for further control implementation. Besides, the CO2 concentration level of exhaust gas is monitored by a CO2 gas sensor, which is mounted on the upper lid. These sensor’s output is connected to an Arduino analog input and sensor readings are displayed on a serial LCD which is attached on the lid of bioreactor. The data is then uploaded in real time to a web server via WiFi by using Arduino WiFi Shield.

To prevent sedimentation of cells at the bottom of bioreactor, we build our own 3D printed slow speed magnetic stirrer which permits gentle mixing of microcarrier cell cultures. The 3D printed magnet bed is designed specifically for two magnets and can be fitted on the DC motor. The stirrer works by using a DC motor to spin two magnets with opposite polarity, which could create a magnetic field in the bioreactor and cause the stir bar to spin and mix the contents. For controlling the speed of the DC motor, we use Arduino and L298N to control the input voltage to the motor by using PWM signal.

The nutrients are pumped into the growth chamber at a rate proportional to the growth factor of the culture, which is determined experimentally through the doubling time of the particular bacterial strain.

About this section, we are showing how to use the pH meter in arduino.
Why we need to use pH meter?
Because E. coli is sensitive to pH value, and according to the experiment of the pH sensor by WET members. (放跟WET連結)We know that E. coli can’t grow below pH value of 6, and generally grow the best about pH 7.

Components And Supplies
1. Arduino UNO
2. pH sensor
(1)Module Power : 5.00V
(2)Measuring Range:0-14pH
(3)Measuring Temperature :0-60 ℃
(4)Accuracy : ± 0.1pH (25 ℃)
3.pH buffer solution

Method of wires
1.pH Meter red wire----Arduino 5V
2.pH Meter ground----Arduino GRD
3.pH Meter yellow wire----Arduino A1
define in code by yourself #define SensorPin A0
4. Wiring diagram

See the code on github

Experiments
Experiment 1:Instrument calibration
1.Experimental method
(1)Insert pH meter into pH 7 buffer solution, wait about 1 min, it will achieve a stable value.
(2)Minus the value with pH 7, and it will get the offset value. For instance,
7-7.09=-0.09

(3)Write the offset value into code, upload the code into Arduino again.

(4) After rinsing the pH meter, insert it into pH 4 buffer solution.
(5) If it is found to be too different from the error of pH=4, you should adjust the knob.
After inserting pH = 4, it is found that the error with 4 is very large.

Adjust the knob
(Remark: Because the change of the knob is small, it may have to turn a few more times until display pH 4.)

Finally, it can be found that the measured pH is 4.

2. Experimental formula calculation
(1)voltage = analog value*5/1024
(2) pH value = 3.5*voltage+offset
See the code on github
Github網址: https://github.com/vicky87106/2018iGEM_NCKU-Tainan
Experiment 2:Precision measurement
1. Experimental Purpose
We assume that pH 4 to 7 is linear, so we want to verify whether it is linear between pH 4 to 7. By measuring the solution of pH 4.7, compare its deviation.
2. Experimental method
Mixing a solution with pH=4.7 and measure with a calibrated pH meter.
3. Result
After inserting the solution with pH=4.7, we found that the value was stable at pH 4.83 with an error of about 0.13, which roughly met the error of this pH meter ± 0.1 pH.