Dissimilatory sulfate reduction as a process to promote denitrification in marine recirculating aquaculture systems

A marine recirculating aquaculture system, the system comprising:

• at least one aquatic species rearing tank, wherein the rearing tank comprises a salt water medium;
• a sludge holding tank positioned downstream from the rearing tank and in fluid communication therewith, wherein the sludge holding tank comprises a media substrate wherein one or more microorganisms active in sulfate reduction are growing on the media substrate;
• a denitrification unit positioned downstream from the sludge tank and rearing tank and in fluid communication therewith, wherein the denitrification unit comprises a media substrate wherein one or more anaerobic microorganisms active in both sulfide oxidization and nitrate reduction are growing on the media substrate;
• and
• a nitrifying moving bed bioreactor positioned downstream from the denitrification unit and upstream of the rearing tank and in fluid communication therewith, wherein the nitrifying moving bed bioreactor comprises a media substrate wherein one or more microorganisms active in nitrification are growing on the media substrate.

A method for reducing and/or removing nitrogenous species from a marine recirculating aquaculture system, the method comprising:

• rearing an aquatic species in a rearing zone containing salt water medium comprising sulfates, ammonia and nitrates;
• filtering the salt water medium from the rearing zone to separate solids from the salt water medium and yield a filtered salt water medium;
• reducing sulfate in the filtered salt water medium to sulfide by action of anaerobic microorganisms adapted for sulfate reduction, to yield sulfide-containing salt water medium;
• oxidizing sulfides in the sulfide-containing salt water medium to sulfates and reducing nitrates in the sulfide-containing salt water medium to nitrogen gas, by action of anaerobic microorganisms adapted to both oxidize sulfides and reduce nitrates, to yield a denitrified saltwater medium;
• reducing ammonia in the denitrified salt water medium, by action of aerobic microorganisms adapted therefore, to yield an ammonia-reduced salt water medium;
• and
• recycling the ammonia-reduced salt water medium to the rearing zone.