Introduction to Recirculating Aquaculture Systems (RAS)

Daniel Miller [email protected]

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 recirculating system.

components in a Discuss the important nitrification systems.

factors in efficient Explain why Identify the rapid solids removal is important 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

Guppy production area UV filter

Return water basin and pH adjustment area

Fluidized bed sand filter Bead Filter 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 NaHCO 3 CaCO 3 will maintain alkalinity.

Temperature: 10 0 C decrease = 50%+ reduction in nitrification rate.

or 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 / m 2 / 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