Nitrate removal in closed-system aquaculture by columnar denitrification

Area of Science:

• Aquaculture Science
• Environmental Microbiology
• Water Quality Management

Background:

• High-density, closed-system salmonid aquaculture generates significant nitrate-nitrogen waste.
• Effective nitrogen removal is essential for maintaining water quality and fish health in intensive aquaculture systems.

Purpose of the Study:

• To investigate the feasibility of columnar denitrification for nitrate-nitrogen removal in closed-system salmonid aquaculture.
• To identify critical parameters for optimizing the columnar denitrification process and ensuring effluent quality.

Main Methods:

• Experimental investigation of a columnar denitrification method using methanol as a carbon source.
• Chemical monitoring of water quality parameters (nitrite, ammonia, sulfide, dissolved organic carbon).
• Scanning electron microscopy to characterize bacterial flora and protozoan consumers.

Main Results:

• Columnar denitrification is feasible but requires precise methanol-to-nitrate-nitrogen ratio control.
• Imbalances led to elevated nitrite, ammonia, sulfide, and dissolved organic carbon, impacting water quality.
• Sulfide production is influenced by column maturity and residence time; methane-carbon and endogenous carbon were unsatisfactory.

Conclusions:

• Optimized columnar denitrification, with careful chemical monitoring, can be a viable method for nitrate-nitrogen removal in salmonid aquaculture.
• Bacterial species like Pseudomonas and Alcaligenes play a key role in the denitrification process.
• Freshwater columns adapted to artificial seawater, and pilot-scale results mirrored laboratory findings, with no nitrite production observed.