Alga-Lung: A Bio-Hybrid Air Purification and Real-Time Environmental Monitoring System

Abstract

Introduction: Indoor air pollution represents an insidious public health threat, as individuals spend up to 90% of their time in enclosed spaces where fine particulate matter (PM2.5), volatile organic compounds (VOCs), and elevated carbon dioxide (CO₂) accumulate. High indoor CO₂ concentrations impair cognitive function, induce fatigue, and exacerbate chronic respiratory conditions. Traditional mechanical air purifiers with HEPA filters offer only a partial fix: they trap dry particles, cannot metabolize CO₂ or release oxygen, and generate non-biodegradable synthetic waste upon disposal.

Biological photobioreactors using microalgae like Spirulina present a regenerative alternative by absorbing CO₂ and releasing fresh oxygen (O₂) via photosynthesis. However, pure biological systems lack real-time feedback, operating as “black boxes” without empirical proof of air quality improvements. This study introduces Alga-Lungan integrated, low-cost (~₹2,000) bio-hybrid system combining a 10-liter liquid Spirulina bubble-column photobioreactor with an Arduino sensor suite to achieve active biological air purification and live environmental data tracking.

Methodology: The bio-hybrid architecture bridges biological purification with embedded telemetry:

• Biological Core: A 10-liter transparent photobioreactor tank filled with an alkaline Spirulina culture. An aquarium air pump continuously drives ambient air bubbles through the liquid, optimizing gas-liquid mass transfer.
• Lighting: A full-spectrum LED grow light provides 12–14 hours of daily illumination to power photosynthesis.
• Sensory Array: An Arduino Uno interfaces with a GP2Y1014AU0F optical dust sensor (PM2.5 tracking) and an MQ-2 gas sensor (smoke/combustible gas detection).
• Telemetry Display: Real-time metrics are rendered continuously on a 16x2 LCD screen.

Biological Cultivation Protocol

1. Media Preparation: Water is enriched with Sodium Bicarbonate (NaHCO₃) and salts to establish a high pH (9.0–10.0), suppressing unwanted bacterial contamination.
2. Inoculation: Pure Spirulina starter culture is introduced at controlled temperatures (28–32°C).
3. Growth Phase: Under LED exposure, the culture undergoes exponential growth, doubling biomass while assimilating dissolved carbon.
4. Maintenance: Bi-weekly harvesting prevents over-density while yielding organic biomass.

Results & Discussion

Empirical testing of the 10-liter Alga-Lung prototype in an enclosed test environment yielded the following performance metrics:

• Rapid AQI Reduction: Within 4 hours of placing and running the active Alga-Lung unit in an enclosed room, the live onboard monitor registered a drop in Air Quality Index (AQI) to a clean reading of 25 (Good/Healthy air quality).
• PM2.5 Capture Efficiency: Trapped 80% to 90% of airborne fine particulates as air bubbles dissolved into the liquid medium, avoiding the clogging issues inherent in paper HEPA filters.
• Gas & Odor Mitigation: Achieved a 75% to 85% reduction in smoke, VOCs, and ambient odors during active sparging cycles.
• Carbon Fixation & O₂ Yield: Reduced room CO₂ levels by 30% to 45%, sequestering 1.8 to 2.0 g of CO₂ for every 1.0 g of dry Spirulina biomass produced.

Literature Benchmark Metrics

Our empirical findings closely align with and validate key metrics reported in microalgae research:

• Cheng & Li (2020): Demonstrated that closed microalgae photobioreactors achieve CO₂ removal rates up to 6.24g/L, with a carbon fixation capacity 10 to 50 times higher than terrestrial plants.
• Han & Wang (2024): Confirmed that indoor Spirulina photobioreactors operating under controlled illumination and alkaline pH (9.5–10.5) sustain CO₂ bio-mitigation efficiencies above 85%, accumulating up to 0.40 g L⁻¹ of dry biomass.

Alga-Lung Performance Data - (PDF)

Conclusion:

The Alga-Lung prototype proves that integrating microalgae culture with low-cost embedded electronics yields a highly effective, circular air purifier for ~₹2,000. Operating in an enclosed room brought the AQI down to 25 within 4 hours, confirming both high PM2.5 capture and rapid gas scrubbing without non-biodegradable filter waste.

Future Horizons

• Biodegradable Materials: The additional Spirulina biomass could be explored as a raw material for developing biodegradable plastic-like materials, reducing dependence on petroleum-based plastics. 
• Biofuel Production: Harvested algae could be studied for its potential use in producing biofuels, giving the biomass an additional useful application. 
• Wireless Monitoring: The Arduino Uno could be upgraded to an ESP32 or Wi-Fi-enabled controller to send air-quality data wirelessly to phones, computers, or online dashboards. 
• Mobile Application: A dedicated mobile app could display live air-quality readings, making monitoring easier and more convenient. 
• Automatic Control: The system could be made automatic, allowing sensor readings to control the air pump, lighting, and other components according to air conditions. 
• Solar Power: Solar panels could be integrated to power the monitoring system and lighting, making Alga-Lung more energy-independent and sustainable. 
• Large-Scale Application: These improvements could help develop Alga-Lung into a more efficient, sustainable, and scalable environmental system for future applications.