Microalgae Growth Phases and Impact of Audible Sound

Growth Phases

Algae growth occurs in five distinct phases:

• Induction
• Exponential
• Declining Relative Growth
• Stationary
• Death

Impact of Audible Sound

Audible sound significantly enhanced the growth rate of Picochlorum oklahomensis during the exponential phase (days 3 to 7). Treated cultures reached the stationary phase 4 days earlier than controls (26 days vs. 30 days).

The highest dry biomass concentration was achieved at 2200 Hz, a frequency common in natural environments, suggesting its optimal effect on enhancing algal biomass production.

Oil Production

Although the average oil content of biomass remained similar between treated and control groups, oil yield per unit volume increased significantly in sound-treated groups. The highest oil content of 27.5% was recorded at 2200 Hz.

Effect of Audible Sound on Haematococcus pluvialis

The blues genre music "Blues for Elle" significantly enhanced the growth and productivity of Haematococcus pluvialis compared to "Far and Wide" and a no-sound control group.

This genre improved cell division and metabolism by influencing:

• Chlorophyll activity
• Nutrient reactivity
• Temperature adaptation

Growth and Productivity Data

Growth rate under "Blues for Elle" increased biomass productivity by 50.94% or 3.467 × 10² cells/mL/day over 22 days.

pH and Proton Dynamics

Audible sound treatments accelerated pH reduction due to increased proton release during photosynthesis.

Supplementary Study

According to this study:

• Frequencies of 200 Hz increased the biomass concentration of Dunaliella salina by up to 50%.
• 200 Hz frequency promoted growth under nitrate deficiency stress conditions.
• 200 Hz combined with nitrate deficiency increased beta-carotene content by 37% compared to the control.

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Local and Global Systems (Vincent and Daniel)

Local System Design

a. Green Algae Carbon Reduction

CO₂ is passed through the algae reactor. Through photosynthesis, green algae synthesize glucose to reduce atmospheric carbon:

12H2O + sunlight → 12H2 + 6O2  [light reaction]
12H2 + 6CO2 → C6H12O6 + 6H2O  [carbon reaction]
    

b. Air Inlet

• Air with high CO₂ concentration is pumped into the algae water under pressure.
• Bubbles refine the gas to increase CO₂ solubility and absorption.

c. Water Entrance

• Circulates algae water to prevent green algae precipitation.
• Lowers temperature for optimal growth conditions.
• Introduces essential nutrients via wastewater.

d. Discharge Port

• Controls water level using overflow port.
• Releases excess oxygen produced during photosynthesis.

e. High Rendering LED Light Tube

Solar panels and biomass energy are used to power LED lights inside the reactor. This allows:

• Night-time photosynthesis and continuous CO₂ recycling.
• Temperature stability from internal LED heat.

Modifications to the Design

• Place LED light inside the container for stable temperature control.
• Install air intake at the bottom to ensure upward airflow through algae.
• Design airflow to enter at the center and exit at the sides of the tank.

System Advantages

• High Adaptability: Applicable in cities, seas, streets, and floors.
• High Mobility: Modular algae species enable easy maintenance and cost reduction.
• Low Maintenance Costs: Efficient and cost-effective carbon sequestration.
• High Benefits: Combines carbon capture with educational and aesthetic urban value.
• Clear Purpose: Alleviates greenhouse effect through atmospheric CO₂ capture.
• Sustainable Operation: Energy and algae cycles are internally sustainable.

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Algae Growth Control System - Sensor and Control Action Plan

1. Audio

Type: Control + Sensing

Action Plan:

• Senses ambient sound waves and the sound of selected music.
• Tracks volume and frequency of music to optimize algae stimulation.

Parameters:

• Volume: To be optimized based on algae species' response.
• Frequency: Example: 200 Hz (D. salina), 2200 Hz (P. oklahomensis).
• Duration:
  • Option 1: Always on
  • Option 2: 12 Hr/day
  • Option 3: Only during daytime

2. Light

Type: Control

Action Plan:

• Control LED lighting using Arduino-based automated switch.
• Replace natural sunlight with LED when unavailable (e.g., night or cloudy conditions).
• Customize LED spectrum to target algae growth while minimizing growth of harmful microorganisms.

Parameters:

• Duration: 12 HR / 24 HR / 8 HR (selectable)
• Spectrum: Custom LED wavelength:
  • 520 nm (green)
  • 550 nm (yellow-green)
  • 600 nm (orange-red)

Potential Issue: Sunlight may boost growth of other microorganisms. Specific LED wavelengths can help prevent biohazard contamination.

3. Turbidimeter

Type: Sensing

Action Plan:

• Detect turbidity or cloudiness in algae water culture.
• Used to track algae biomass increase over time (more growth = higher turbidity).

Frequency:

Every 6 hours.

4. Temperature

Type: Control + Sensing

Action Plan:

• Monitor water temperature regularly.
• Trigger cooling or heating systems if temperature is outside the algae growth range.
• Low temperature slows growth (reflected by lower turbidity).
• High temperature may denature algae cells and lead to cell death.

Frequency:

Every 5 minutes.

5. pH Level

Type: Sensing

Action Plan:

• Use a pH meter (or "pH propermeter" if available) to measure water acidity.
• Monitor pH in saltwater-based algae cultures.

Frequency:

Once per day.

6. Power Consumption

Type: Sensing

Action Plan:

• Monitor power usage from each component.
• Focus on high consumption parts like speakers and LED lights.
• Log energy use every 5 minutes to track system efficiency.
• Plan to integrate solar charging in the future for sustainable energy supply.

Frequency:

Every 5 minutes.

System Integration

By combining the code we wrote with the devices on the breadboard, we eventually concluded that there are three essential components of the breadboard: the power supply, the audio input and output, and the time module that controls the temperature and the turbidimeter.

ESP-32 Power Supply System

I’ve learned how to connect different devices (OLED display, INA3221, and the power supply) to the main ESP-32. The main function of the system is to support other devices on the breadboard with power.

OLED Display

The OLED display shows the voltage, current, and power of other devices, which update every second. This is done through the help of the INA3221, which measures the voltage and current on all devices, then sends the data to the OLED display.

INA3221 and Power Supply

The power supply is connected mostly to the INA3221, while other connections go to the three ESP-32 units. There is a positive and a negative wire labeled on the power supply as VDD and GND. VDD is the positive terminal and stands for Voltage at the Drain, while GND is the negative terminal and stands for Ground.

Every device has its own VDD and GND. If you misconnect the wires, the entire system could be damaged or burnt out.

Sensor Module for Algae Tank

This part of the module consists of six different components: Light Intensity Sensor, SD Memory Card, Time Module, Thermometer, Turbidimeter, and OLED Display, all connected to the ESP32 microcontroller.

This module serves as the stats collecting center, gathering various types of data from the algae tank. The collected data is displayed on the OLED display and uploaded to IFTTT, a cloud drive.

Components and Functions

GY-30 Light Intensity Sensor

Located at the top left in the setup, the GY-30 module detects the surrounding light intensity. Once measured, the data is sent to the ESP32 and then displayed on the OLED display.

SD Memory Card

The SD card gathers and stores all collected information and later uploads it to IFTTT for cloud storage.

DS1302 Time Module

The DS1302 module functions as an internal clock for the system. It allows other components to operate based on time intervals and ensures the system follows the programmed schedule.

Thermometer

The thermometer detects the water temperature and sends the data to the ESP32, which then displays it on the OLED.

OLED Display

The OLED screen presents all information sent from the ESP32, including light intensity, temperature, turbidity, and more.

Turbidimeter

Although the turbidimeter may appear simple, it poses a significant challenge. To prevent malfunction caused by the saltwater in the tank, air pockets inside the sensor must be filled with epoxy resin. After measuring turbidity, the sensor sends the data to the ESP32, which then forwards it to the OLED display.

Audio Module

The audio module consists of five main components: Microphone, Speaker, MP3 Player, Volume Control, and an OLED Display, all connected to the ESP-32 microcontroller.

This system performs two main functions: music playback and sound detection.

Music Playback

To play music, an SD card is inserted into the MP3 player. The MP3 player is connected to the volume control module, which is then connected to the speakers. It is also connected to the ESP-32 microcontroller, which sends track information to the OLED display for visual feedback.

Sound Detection

For sound detection, the microphone sends audio signals to the ESP-32 microcontroller. The microcontroller processes this information and sends it to the OLED display. Additionally, it connects to Channel 3 of the power meter, allowing the power module to monitor the system's power consumption during operation.