1. Introduction to Recirculating Aquaculture Systems (RAS)
Daniel Miller
Florida A&M University
Farmer to Farmer Program
Stellenbosch, South Africa
February, 2010

2. Objectives
After participating in this discussion participants will be able to:
List and describe advantages and disadvantages of recirculating systems.
List and describe the various components in a recirculating system.
Discuss the important factors in efficient nitrification systems.
Explain why rapid solids removal is important.
Identify the driving force in the system.

3. Recirculation Systems Developed from wastewater treatment plants
Advantages
Greatest control
Flexible locations
Waste control
Minimal space / water
Efficient production
Disadvantages
Increased cost
Technical knowledge
Power required
Back up power needed
Must oxidize ammonia and nitrite to nontoxic form (nitrate).
Must remove CO2 and add O2.
Must concentrate / remove solid wastes from the system ASAP.
May remove fine solids (<30microns) and dissolved organics.
May disinfect to control disease.

4. WV Aqua’s Arctic char recirculating production farm

5. Cornell-type dual drain For rapid concentration and removal of solids
Low volume (10%)– High solids center drain
High volume (90%) – Low solids side drain

6. 10,000 gallon recirculating (200gpm) tropical fish
Fluidized bed sand filter
Guppy production area
Bead
Filter
UV filter
Return water basin
and pH adjustment area
10,000 gallon recirculating (200gpm) tropical fish
production system in Uniontown, PA (USA)

7. Recirculation Systems Required Components or Processes
Solid removal: double drains, sedimentation, drum filters, bead filters.
Biological Filter: fluidized bed, Rotating Biological Contacter, trickle.
Aeration: airstone, packed column, Low Head Oxygenator, U-tube
Dissolved organics/ fine particle removal: Foam fractionation, cartridge filters.
Disinfection: ozone, ultraviolet radiation (UV).
Production tanks: round or rectangular?…advantage round.
How much flow is needed? Rule: 41 liters / kg. of daily feed
Converting 1 gram of ammonia requires 4.5 gm oxygen and 7.1 gm alkalinity

8. Factors in Nitrification (ammonia conversion)
pH: 6 – 9 ; stability is important
Alkalinity: >50 ppm Regular additions of NaHCO3 or CaCO3 will maintain alkalinity.
Temperature: 100C decrease = 50%+ reduction in nitrification rate.
Oxygen: effluent from biofilter > 2 ppm
Ammonia is the energy source for bacteria
Available surface area for bacteria:
Conversion rate: 0.2 – 1.0 gm / m2 / day

9. Protein (N) in Feed is the Driving Force in ammonia production.
Every 100 kg of feed added to the system will result in 2.5 to 3 kg of ammonia.
Every gram of ammonia will result in 4.5 grams of oxygen use and 7.1 grams of alkalinity used.

10. Rotating Biological Contactor
Partially submerged discs rotate in system water
Nitrifying bacteria grow on surface of discs.
Outer edge moves at 15 meters per minute (2-4 rpm)
Increases oxygen
Reduces CO2
Self-cleaning
Expensive
Can become very heavy.

11. Bead Filter:
Removes solids
(>60 microns) and provides ammonia control (biofiltration).

12. Fluidized Bed Sand Filter
Cultivates bacteria, which
convert ammonia into
non-toxic nitrate.
Very efficient
Does not remove solids!

13. Rotating Drum Filter:
Self cleaning
High water volumes
60 micron particle removal
Compact and low water loss
Costly

14. Trickle Filters Provide aeration and CO2 removal
Can become clogged with suspended solids
Can become very heavy over time.
Are most successful with smaller systems
that have variable feeding rates.

15. Denitrification in Recirculating systems
Removing nitrate (NO3) to N (gas)
Technology is improving
Consult a bio-engineer for
design limits.
Used for sensitive species

17. Additional Resources A Fish Farmers Guide to
Understanding Water Quality:
Aquaculture Network Information Center:
WVU Aquaculture website:
Aquatic Eco-Systems –