Mass transfer and flow characterization of novel algae-based nutrient removal system

Area of Science:

• Aquaculture Engineering
• Biotechnology
• Environmental Science

Background:

• Recirculating aquaculture systems (RAS) face challenges with nutrient removal, impacting sustainability and cost-effectiveness.
• Existing nutrient removal methods offer limited added value options.
• An innovative, energy-efficient algae-based nutrient removal system (NRS) was developed to address these issues and enable algal commercialization.

Purpose of the Study:

• To design, manufacture, and test a novel algae-based nutrient removal system (NRS) prototype.
• To optimize mass transfer using novel aeration and mixing technology for continuous nutrient removal and algae production.
• To assess the scalability and economic viability of the NRS through algal commercialization.

Main Methods:

• Developed a 60-L NRS prototype with airlift pumps and a novel membrane cartridge.
• Optimized mass transfer by examining airlift mixing conditions, concentration gradients, and internal bioreactor geometries.
• Assessed nutrient removal capacity and algal growth rates using the green alga Dunaliella tertiolecta.

Main Results:

• Achieved an overall mass transfer coefficient in the range of 0.00164-0.0074 [Formula: see text], with optimal mass transfer at a Reynolds number of 500.
• Demonstrated adequate mixing and even distribution of dissolved oxygen, crucial for algal growth.
• Confirmed effective nutrient removal from wastewater and comparable algal growth rates to existing systems.

Conclusions:

• The novel NRS effectively removes nutrients from aquaculture wastewater using algae.
• A threefold increase in mass transfer rate was observed with a 2.5-fold increase in concentration gradient, highlighting the role of airlift mixing.
• The system's design is scalable and offers potential for revenue generation through algal commercialization, supporting sustainable aquaculture.