Tag Thomas M. Losordo

The water quality in recirculating aquaculture systems is generally a function of the tank size, biomass, feed inputs and waste treatment efficiency. Adequate biofiltration can control the build-up of ammonia-nitrogen and nitrate-nitrogen in the systems. 

An important criterion when studying biofilters is the conversion rate of total ammonia nitrogen (TAN) to nitrate-nitrogen in production water. Although nitrification rates have been based on media surface areas, they do not always reflect the actual nitrification achieved. Volumetric TAN conversion rate is a direct measure based on filter volume. 

To start a biofilter together with a source of nitrifying bacteria, you must provide the conditions that will encourage the growth of the bacteria. The basic process requires initial preparation of water chemistry, adjustment of alkalinity to support bacterial growth and the addition of ammonia. 

Biological filtration is one of the critical required unit processes in recirculating aquaculture systems. Non-corrosive filter media with large amounts of surface provides area for nitrifying bacteria cells to colonize. 

Geotextile bags used in combination with polymer flocculant aid chemicals can provide effective primary treatment of recirculating aquaculture system effluent. Much of the suspended solids that carry the majority of the organic load within the effluent can be captured by these systems. 

For most effective use, water should have low turbidity and high U.V. transmittance, with ultraviolet dosage tuned to the target organisms. Low-pressure/high-output amalgam U.V. lamps are often used in RAS systems. 

The ability to maintain adequate oxygen levels can be a limiting factor in carrying capacities for RAS. The amount of oxygen required is largely dictated by the feed rate and length of time waste solids remain within the systems. 

Since un-ionized ammonia-nitrogen and nitrite-nitrogen are toxic to most finfish, controlling their concentrations in culture tanks is a primary objective in the design of recirculating aquaculture systems. 

A model designed at the University of North Carolina at Wilmington examines the profitability of summer flounder aquaculture using recirculating systems. 

Grow-out studies of summer flounder at the University of North Carolina Wilmington evaluated microbead media as a biofilter in recirculating systems.