Intensive Tank Culture of Tilapia in the UVI Biofloc System

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Intensive Tank Culture of Tilapia in the UVI
Biofloc System

• James Rakocy, Donald Bailey
• Charlie Shultz and Jason Danaher
• University of the Virgin Islands
• Agricultural Experiment Station
• St. Croix, U.S. Virgin Islands

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Objectives

• Evaluate the production of tilapia in a 200-m3
  tank employing aeration, solids removal, mixing,
  bacterial-based treatment in the water column,
  and denitrification.
• Modify and improve the system during the course
  of three production trials.

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Initial Tank Design

• Size 200 m3, 16 m diameter, 1 m mean water depth
• Surface area 200 m2 (0.02 ha or 1/20 acre)
• Bottom 3o slope to center
• Center clarifier 1 m3, 45o slope, fiberglass,
  10-cm drain
• Outside standpipe for solids removal
• Aeration three ¾-hp Kasco aerators
• Water movement one ¾-hp Kasco aerator angled

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Biofloc Tank
16 m
1.09 m
Total Culture Volume 200 m3
0.15 m Freeboard
3º Slope
Sludge Cone Volume 1.0 m3
Sludge Removal Line
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Biofloc Tank
Aeration device
Central cone
Base addition tank
Drain
Flow
Sludge collection and measurement
To storage lagoon
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Procedures

• Aeration continuously
• Mix continuously to maintain suspension of
  biofloc
• Remove settleable solid waste daily
• Feed twice daily with floating feed (32 protein)
• Feed ad libitum for 30 60 minutes
• Monitor pH daily, maintain pH 7-7.5 with Ca(OH)2
• Add CaCl2 to prevent nitrite toxicity
• Monitor important water quality parameters

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Aeration with vertical lift propeller pumps
Clear well water before stocking
Established with biofloc and algae
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Total Suspended Solids Settling Curve
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Clarifier Efficiency
Clarifier effluent Culture tank water Sludge from
clarifier
After 10 minutes of settling
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External Clarifier Efficiency
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Sludge Removal in Last 21 Days
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Total Suspended Solids Trial 2(with external
clarifier)
(1744)
(600)
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Total Suspended Solids
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Greenwater Tank Trial 3
Denitrification tanks
Base addition tank
Aeration devices
Pump
Flow
Clarifier
Horizontal mixer
Sludge removal to storage lagoon
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Denitrification

• 5 HOAc 8NO3- 4N2 10CO2 6H2O 8OH-
• Must have a carbon source e.g., acetate
• Denitrification recovers the alkalinity that is
  lost during nitrification.

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Production
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Major Inputs and Outputs
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TSS Trial 2 and 3
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Nitrate-Nitrogen Trial 1 - 3
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Biofloc Tank Culture Advantages

• Simple management
• Low water requirements
• Algal die-offs do not cause mortality
• Algae and bacteria supplement tilapia diet
• No off-flavor detected
• Production 30 times higher than ponds for
  tilapia
• No recruitment problem
• Wastewater used to irrigate and fertilize field
  crops

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Biofloc Tank Culture Disadvantages

• Requires a 6-week period to establish bacterial
  populations
• Suspended solids nitrification less stable than
  fixed-film nitrification
• Feeding response fluctuates
• Algal die-off reduces feeding response
  temporarily
• High energy input
• Reliance on continual aeration and mixing
  requires backup power

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Key Results

• Total tilapia production (3060 kg in 1/50-ha
  tank)
• Daily makeup water averaged 0.29 (0.59 m3) of
  total water volume
• Recovered approximately 36 (0.21 m3) of daily
  makeup water for irrigation and fertilization of
  field crops.

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Conclusions

• This biofloc tank process was nearly 30 times
  more productive than a standard earthen pond
  (15.3 vs. 0.5 kg/m3)
• External clarification simplifies tank
  construction, improves solids removal and water
  quality and increases production
• Simple open channels with solids accumulation can
  provide adequate denitrification
• This production technology conserves water and
  recovers solids and nutrients

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Design and Operation of the UVI Aquaponic System

• James Rakocy, Donald Bailey
• Charlie Shultz and Jason Danaher
• University of the Virgin Islands
• Agricultural Experiment Station
• St. Croix, U.S. Virgin Islands

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System Layout
Base addition
Hydroponic tanks
Effluent line
Degassing
Rearing tanks
Sump Clarifier Filter tanks
Return line
Total water volume, 110 m3 Land
area - 0.05 ha
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System Design

• Four fish rearing tanks, 7.8 m3 each
• Two cylindro-conical clarifiers, 3.8 m3 each
• Four filter tanks, 0.7 m3 each
• One degassing tank, 0.7 m3
• Six hydroponic tanks, 11.3 m3 each
• Total plant growing area, 214 m2
• One sump, 0.6 m3
• Base addition tank, 0.2 m3
• Total water volume, 110 m3
• Land area - 0.05 ha

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Treatment Processes

• Air stones, 22 per rearing tank, 24 per
  hydroponic tank
• Solids removal, three times daily from
  clarifier, filter tank cleaning one or two
  times weekly
• Denitrification in filter tanks
• Continuous degassing of methane, CO2 , H2S, N2
• Direct uptake of ammonia and other nutrient by
  plants
• Nitrification in hydroponic tank
• Retention time rearing tank, 1.37 h clarifier,
  20 min, hydroponic tanks, 3 h

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Treatment Characteristics

• Removal rates using romaine lettuce
  (g/m2/d)NH3-N, 0.56NO2-N, 0.62COD, 30.3Total
  nitrogen, 0.83Total phosphorous, 0.17

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Important Principles

• Optimum feeding rate, 60 - 100 g/m2 plant
  area/day prevents nutrient accumulation or
  deficiency
• Slow removal of solids increases mineralization
• Frequency of filter tank cleaning controls
  nitrate levels through denitrification
• Treatment capacity of hydroponic tanks is
  equivalent to 180 g of feed/day/m2 of plant area

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Production Management

• Feeding three times daily ad libitum 32
  protein, floating, complete diet
• Stagger fish production, 24 week cycle, harvest
  every 6 weeks
• Stagger plant production
• Use biological insect control
• Monitor pH daily, maintain pH 7.0 by
  alternate and equal additions Ca(OH)2 and KOH
• Add chelated iron (2 mg/L) every 3 weeks
• Add makeup water daily, about 1.5 of system
  volume
• Purge fish for 4-5 days before sale

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Energy Consumption

• One blower for fish and degassing, 1.5 hp
• One blower for hydroponics, 1 hp
• One water pump, ½ hp
• Total energy consumption 3.0 hp

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Production

• Tilapia - 5 mt annually , 580 kg every 6 weeks,
  160 kg/m3/yr
• Stocking rate Niles, 77 fish/m3 reds, 154
  fish/m3
• Leaf lettuce - 1,404 cases annually, 24-30
  heads/case, 27 cases/week
• Basil 5 mt annually
• Okra 2.9 mt annually

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Advantages of Aquaponics

• Fish provide most nutrients required by plants
• Plants use nutrients to produce a valuable
  by-product
• Hydroponic component serves as a biofilter
• Hydroponic plants extend water use and reduce
  discharge to the environment
• Integrated systems require less water quality
  monitoring than individual systems
• Profit potential increased due to free nutrients
  for plants, lower water requirement,
  elimination of separate biofilter, less water
  quality monitoring and shared costs for
  operation and infrastructure.

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Perspective on UVI Aquaponic System

• The system represents appropriate or intermediate
  technology
• It conserves water and reuses nutrients
• The technology can be applied at a subsistence
  level or commercial scale
• Production is continuous and sustainable
• The system is simple, reliable and robust
• Management is easy if guidelines are followed

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