How Heat Transfer Indirectly Affects Performance of Algae-Bacteria Raceways

Area of Science:

• Environmental Engineering
• Microbiology
• Chemical Engineering

Background:

• High energy consumption for oxygenation in conventional wastewater treatment.
• High-rate algal-bacterial ponds (HRABP) utilize microalgae photosynthesis for oxygen, reducing energy costs.
• HRABP efficiency is sensitive to environmental factors like solar flux, light, and temperature, which vary seasonally and geographically.

Purpose of the Study:

• To develop a predictive model for temperature evolution in HRABPs.
• To assess the impact of different reactor configurations (raised vs. ground-level) and water depths on HRABP temperature patterns.
• To evaluate the consequences of temperature dynamics on HRABP performance and stability.

Main Methods:

• Utilized the validated algae-bacteria (ALBA) model for algal-bacterial dynamics.
• Coupled the ALBA model with a newly developed heat transfer model to predict water temperature.
• Validated the integrated model using long-term outdoor measurements across different seasons and locations.

Main Results:

• The heat transfer model accurately predicted HRABP water temperature with a standard error of 1.5 °C.
• The fully predictive model showed a minor degradation (<3%) in overall performance.
• Nitrous oxide (N2O) predictions were sensitive to temperature variations (±7%), indicating nitrification sensitivity.
• Raceway configurations not lying on the ground and shallower depths exhibited more extreme temperature events, increasing the risk of culture crashes.

Conclusions:

• The developed predictive model enhances understanding of temperature impacts on HRABPs.
• Reactor design and water depth significantly influence temperature dynamics and operational stability.
• Optimizing HRABP configuration is crucial for maintaining stable performance and preventing culture crashes due to temperature fluctuations.