Nearly 40% of CO2 emissions are attributable to industries. The goal of our project is to solve the CO2 problem by using engineered E.coli to fix carbon dioxide emitted from industries and convert it into bio-product, pyruvate. To accomplish our goal, we designed a device that will upscale our project to be used on field and we aim to integrate the device into industrial IGCC system. And we used the Arduino to sense the pH, CO2 concentration and temperature then use the wi-fi sensor to upload to the database.Last but not least, we can monitor the data by our app.

Our device consists of 4 main parts: a bioreactor, a nutrient tank, a collection tank and Arduino.The flue gas contains high concentration of CO2 and this will inhibit the growth of E.coli. Thus, we reduce CO2 concentration level to less than 5% before entering the bioreactor by using flowmeter, which is an instrument for measuring the flow of gases in pipelines.

For Arduino, we use temperature sensor(DS18B20)、pH meter and CO2 sensor(MG811) to monitor our device. Besides, we use LCD to print datum and use Wi-Fi sensor(ESP8266 Nodemcu) to upload our records to database as well. (You can see more information about Arduino code in software.)

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
Method of wires

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
3. 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.

Why we need to use CO2 Sensor?
We want to detect if the CO2 concentration at the outlet is decreasing as expected.

Material used

1. Arduino UNO
2. MG811 CO2 Sensor
3. Datasheet
• (1)Heating power supply: 7.5-12V
• (2) Operating Temperature: -20 – 50 °C
• (3) Measuring range: 400-10000ppm CO2
4. Float flowmeter

Wiring

1. MG811 CO2 Sensor red line----external battery red line
2. MG811 CO2 Sensor Black Wire----External Battery Black Line
3. MG811 CO2 Sensor Yellow Line----Arduino A0
• Remarks: Define yourself in code #define SensorPin A0

Wiring diagram:

See the code on github

Experiment

• Experiment 1: Instrument calibration
1. Experimental purpose:
• Because the analog value returned by each sensor may be inaccurate, and the carbon dioxide concentration in each area may be slightly different, it must be corrected before use.
2. Experimental method:
• (1) Connect the power supply to 3.3V and use arduino to measure the analog value of output A0. Its stable value is about 3.3/5*1024=675.84.
• (2) Let the sensor enter a steady state and operate in an unventilated environment for at least 48 hours.
• (3) At this time, the analogy value of the atmospheric carbon dioxide concentration (about 400 ppm) was measured, and we measured 705.
• (4) The known carbon dioxide concentration is adjusted by a float flowmeter, and the ppm can be obtained according to the formula conversion, and the analogy value of the concentration is obtained.
• Ex: We put the carbon dioxide sensor into 100% carbon dioxide and measured its analogy value to 260.
• (5) We assume that the carbon dioxide logarithmic concentration is negatively linearly related to the output analog value, and can be found by the known two points.
3. Experimental formula:
• Experiment 2: CO2 trend line verification
1. Experimental purpose: to verify whether the logarithmic concentration of carbon dioxide is negatively linear with the output analog value.
2. Experimental method:
• Use a float flowmeter to call up the known carbon dioxide concentration and measure its analogy to see if it is on this line.
3. Experimental results:
• 還沒做這星期做完實驗補

Precautions

It is best to preheat for the first time for 24 hours, use it for more than six hours, preheat for 1-2 hours, power off for more than 72 hours, and preheat for 24 hours.

About this section, we are showing how to use DS18B20 one wire water proof temperature sensor.
Why we need to use temperature sensor?
Because E. coli is sensitive to temperature sensor. According to the experiment, it grows the best in 37°C (99°F), and its acceptable range is about 22 to 40°C (72 to 104°F). Therefore, we need temperature sensor to monitor our medium's temperature.

Components And Supplies

1. Arduino UNO
2. DS18B20 temperature sensor
• (1)Power supply range is 3.0V to 5.5V
• (2)Measures temperatures from -55°C to +125°C (-67°F to +257°F)±0.5°C accuracy from –10°C to +85°C (14 to 185°F)
3. a register of 4700 ohms

Method of wires

1. DS18B20 red wire----Arduino 5V
2. DS18B20 ground----Arduino GRD
3. DS18B20 yellow wire----Arduino 2 define in code by yourself #define ONE_WIRE_BUS 2
4. Wiring diagram

Experiment

• Experiment 1: Temperature measuring
• Experimental purpose:
• We want to know the error between the actual temperature of the incubator and the temperature measured by the sensor.
• Experiment method:
  
  • We put our temperature sensor into the incubator. We wire the sensor with the LCD to keep it closed.
• Experimental purpose:
• We placed the sensor in an environment of incubator 37 degrees, and the temperature measured by the LCD display sensor was 37.06 degrees. The error is 0.06 degrees, which we think is not big. But in order to make the measured temperature more accurate, we designed the second experiment - Temperature experimental curve fitting.
• Experiment 2: Temperature experimental curve fitting
• Experimental purpose:
• Since the error value of the temperature sensing device is not necessarily, we use multiple sampling methods, and then average the values measured in each temperature interval to reduce the error value without excessive error.
• Experiment method:
• We use the above method to take 150 strokes as training data, and use the basic accessories of MATLAB to find the appropriate nine temperature model formulas.
• Experimental purpose:
• We found a 7th degree temperature curve to reduce its error. (You can see more information in software temperature.)

我們做完wi-fi的時候補!!QQ

• Acrylic Sheet
• Arduino UNO
• Power Supply
• Batteries
• Rotameter
• pH meter
• Thermometer(DS18B20)
• CO2 sensor(MG811)
• Wi-fi sensor(ESP8266 NodeMcu)
• Geared DC Motor
• Tubes
• Magnets
• 3D Printed Structure
• Nuts and Screws
• Wires
• Pumps

(1)pH meter:
Boywhy Chen.(2016).[Arduino] PH meter. Retrieved from
http://boywhy.blogspot.com/2016/07/arduino-ph-meter.html(Augest 28,2018)
(2)temperature(DS18B20 ):
Konstantin Dimitrov.(2016).Arduino Thermometer With DS18B20. Retrieved from
https://create.arduino.cc/projecthub/TheGadgetBoy/ds18b20-digital-temperature-sensor-and-arduino-9cc806
(3)CO2 sensor(MG811):
Tiequan Shao.Peng Wei.(2016)Arduino 二氧化碳感測器MG811 校正計算.Retrieved from
http://a-chien.blogspot.com/2016/03/arduino-mg811.html