Introduction to Recirculating Aquaculture Systems (RAS) Daniel Miller dmille31@wvu.edu Florida A&M University Farmer to Farmer Program Stellenbosch, South Africa February, 2010

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.

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.

WV Aqua’s Arctic char recirculating production farm

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

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)

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

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

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.

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.

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

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

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

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.

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

Additional Resources A Fish Farmers Guide to Understanding Water Quality: http://darc.cms.udel.edu/AquaPrimer/wqualityas-503.pdf Aquaculture Network Information Center: www.aquanic.org/oindex.htm WVU Aquaculture website: www.wvu.edu/~agexten/aquaculture/index.htm Aquatic Eco-Systems – www.aquaticeco.com