# Proposal of a Laboratory-Scale Anaerobic Biodigester for Introducing the Monitoring and Sensing Techniques, as a Potential Learning Tool in the Fields of Carbon Foot-Print Reduction and Climate Change Mitigation

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

_{4}capture and fossil fuel replacement, is clearly a factor to take under advisement [1,2,3,4,5,6,7]. The process of anaerobic digestion has been known and applied since ancient times; however, it was understood in terms of its final products and not its processes [3]. The versatility of anaerobic digestion applied as an effective technology in the face of certain fundamental challenges has found its usefulness in biotechnological industries [4,5,6,7]. Unlike aerobic processes where dissolved oxygen can be measured continuously, there is a great challenge for fermentative processes in anaerobic organisms where the technologies referring to control processes are currently insufficient [6,7,8,9,10]. Since pH detection has been commonly used in fermentation processes, where only the activity of the proton is reflected, it is not sensitive to small changes in the intracellular metabolism. The redox potential (ORP) known as oxidation-reduction or oxide-reduction potential, reflects all the electrons transferred and reflects the intracellular metabolism [6,11,12,13,14,15].

## 2. Materials and Methods

#### 2.1. Diagram of the Laboratory Reactor

#### 2.1.1. Digestion System

- pH Sensor: Scientific Grade Silver/Silver Chloride pH), 10 sensor with a response speed of 95% in one second.
- Absolute Pressure Sensor: Phidgets mod. 1141-0—Absolute Sensor of gas pressure from 15 to 115 kPa [49,50]. This is a high-level sensor with analogue input, with input proportional to the of the environment. The pressure measurement for this sensor is 15 kPa. The formula used to translate the sensor value into pressure was the following [2,51,52]:

^{−5}x

^{2}+ 0.06872x − 16.03

#### 2.1.2. Circuits and Control System

#### 2.1.3. Computer System, Communication Interface, and Software

#### 2.1.4. Auxiliary Equipment and Laboratory Material

#### 2.2. Preparation and Testing

#### 2.2.1. Preparation of the Substrate

#### 2.2.2. Microbial Inoculum

#### 2.2.3. Control and Saving Data

## 3. Results

#### 3.1. Digestion Model

#### 3.2. Anaerobic Digester Start-Up and Operation

^{0}is the standard ORP, n is the number of exchanged electrons, and F is the Faraday constant (96.42 kJ/g equivalent volts).

#### 3.2.1. First Stage

#### 3.2.2. Second Stage

#### 3.2.3. Third Stage

## 4. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Appendix A. SCILAB Source Code

## Appendix B. Microcontroller Source Code (Arduino)

## Appendix C. Processing Source Code

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**Figure 7.**Concentration of biomass and substrate where ${\mu}_{max}=0.75({\mathrm{h}}^{-1}),{K}_{s}=10,{\beta}_{s}=1.8$, X

_{(t=0)}is 0.1 (g/m

^{3}) and S

_{(t = 0)}is 4 (g/m

^{3}).

Parameter | Value | Units |
---|---|---|

Resistence value at 25 °C | 10 K | Ω |

Tolerance of R25 | ±3 | % |

B25/85 (Beta) | 3984 | K |

Temperatura range of operation | −25 to 105 | °C |

Stage | Date | Feeding/Evacuation | Brix Grades | Remarks | ||
---|---|---|---|---|---|---|

(mL) | 1st Lecture | 2nd Lecture | Average | |||

1 | 13 June | 300 | 20.30 | 20.30 | ||

2 | 18 June | 75 | 20.31 | 20.29 | 20.30 | |

3 | 23 June | 50 | 20.33 | 20.24 | 20.26 | Addition NaOH (↑alkalinity) |

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**MDPI and ACS Style**

Brito-Espino, S.; Leon, F.; Vaswani-Reboso, J.; Ramos-Martin, A.; Mendieta-Pino, C. Proposal of a Laboratory-Scale Anaerobic Biodigester for Introducing the Monitoring and Sensing Techniques, as a Potential Learning Tool in the Fields of Carbon Foot-Print Reduction and Climate Change Mitigation. *Water* **2021**, *13*, 2409.
https://doi.org/10.3390/w13172409

**AMA Style**

Brito-Espino S, Leon F, Vaswani-Reboso J, Ramos-Martin A, Mendieta-Pino C. Proposal of a Laboratory-Scale Anaerobic Biodigester for Introducing the Monitoring and Sensing Techniques, as a Potential Learning Tool in the Fields of Carbon Foot-Print Reduction and Climate Change Mitigation. *Water*. 2021; 13(17):2409.
https://doi.org/10.3390/w13172409

**Chicago/Turabian Style**

Brito-Espino, Saulo, Federico Leon, Jenifer Vaswani-Reboso, Alejandro Ramos-Martin, and Carlos Mendieta-Pino. 2021. "Proposal of a Laboratory-Scale Anaerobic Biodigester for Introducing the Monitoring and Sensing Techniques, as a Potential Learning Tool in the Fields of Carbon Foot-Print Reduction and Climate Change Mitigation" *Water* 13, no. 17: 2409.
https://doi.org/10.3390/w13172409