Bowling Green Satellite Aquaculture Center

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Bowling Green Satellite Aquaculture Center

Introduction to Recirculating Aquaculture
Workshop
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Critical Considerations in Recirculating
Production Systems

• Definition
• An aquaculture
• production system
• that recycles and
• renovates water for
• the culture of aquatic
• organisms

• Categories of Recirc. Systems
• Semi- closed system
• 5 exchange per pass
• 120 exchange per day
• Closed system
• 0-20 volume change per day (typical of systems
  being designed today)

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Recirculating System Pros and Cons

• PROS
• Less water needed
• Less land needed
• Temperature Control
• Water Quality Control
• Waste Retention
• Better feed Conversion
• Product Isolation
• Inventory Control

• CONS
• High Initial Investment
• compared to other technologies
• No existing standard protocols
• Short Response time
• THINGS GO WRONG FAST !
• No track record

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The Recirc. Golden Rule

• Do Not Be Impressed By Fish Held at High
  Densities.
• Fish can be held at high densities, in even
  poorly designed systems, if they are not fed .
• Be Impressed By High Feed Rates per Day
• Remember it takes Feed to Raise Fish
• Daily Weight Gain Daily Feed Rate / Feed
  Conversion Ratio
• ITS THAT EASY!!!

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Feed Effects on Water Quality

• Feeds Impact On Water Quality Is Almost Always
  NEGATIVEInputs and Outputs Based on the Input
  of 1Kg of Feed

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But Why Mention Feed Now?

• Feed is needed to grow fish (no brainer)
• Feed will determine the inputs required to
  maintain proper water quality
• Feed will also determine the amount of waste
  products that also need to be dealt with to
  maintain water quality
• So lets look at the general water quality
  parameters we need to meet to insure a healthy
  environment

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General Water Quality Parameters

• Dissolved Oxygen (O2) (mg/l) gt 6.0
• Carbon Dioxide ( CO2 )(mg/l) lt 20
• pH
  6.5-8.0
• Alkalinity (mg/l)
  100-300
• Ammonia (NH3) (mg/l) 0.02-0.05
• Nitrite (NO2)(mg/l) 0.2-5.0
• Nitrate (NO3) lt1000
• Suggested average for culture tank, O2 should
  not fall below 4 mg/l anywhere within the system

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Feed and Water Contin.

• Inputs
• 0.25-1kg Oxygen
• 0.18-0.4 Kg Alkalinity
• (usually Sodium Bicarbonate)

• Outputs
• 0.35-1.38 Kg CO2
• 0.25-0.5 Kg Waste Solids (dry weight)
• 0.025-0.055 Kg NH3 NH4

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Water Treatment

• Solids Removal (Round Tank Hydraulics and
  Filtration)
• First, as always, definitions!
• Settleable Solids Under quiet conditions these
  solids will settle from the water column in 1
  hour
• Suspended Solids Solids that will not settle out
  in one hour under quiet conditions

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Water Treatment Continued

• Hydraulic Retention Time (HRT) Tank Volume
  Divided by Inflow Rate (Qin)
• EXAMPLE 20,000 liter (5,283 gal) / 333lpm (88
  gpm) 60 minutes
• In actuality this HRT is a mean or average
• To turn the entire volume of the tank over would
  take 1.6 hours!

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How Do Round Tanks Work For us?

• Simple to maintain
• Provide uniform water quality
• Allow operation over a wide range of water
  velocities to optimize health and condition
• Settable solids can be rapidly flushed to the
  center drain

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Hydraulics

• First lets look at water in flow and tank
  dimensions
• The optimum tank should have a diameter to depth
  ratio of 31
• With this ratio we also utilize a vertical
  manifold to deliver water to the culture vessel
• This combination allows for what is called a tea
  cup effect
• The friction between the tanks walls and water
  form a secondary rotation which will rapidly move
  settable solids to the center drain
• Now if we couple this effect with a double drain
  we can de-couple the HRT for suspended and
  settleable solids!!!!

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Vertical Manifold

• The vertical manifold extends to the bottom of
  the tank as shown right
• This allows for better mixing within the tank as
  well as assisting in the tea cup effect
• Velocity should not exceed Vs
• Vs Safe swimming velocity in body lengths per
  second
• Vslt 5.25 L 0.37

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• Flow A 85-90 of flow
• Flow B 15-20 of flow

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So we have removed the solids from the tank ! Now
what?

• Suspended Solids
• One of the most effect methods
• Drum Screen filtration

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Drum Screen Operation
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Settleable Solids

• 15 of flow
• Referred to as a swirl separator or hydrocyclone
• Discharge from SS re-enters flow to drum screen
  filter

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Lets look at it all together
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Bio-filtration

• The term bio-filtration refers to using a
  biological process to remove or convert a
  targeted substance
• In the case of Recirc. systems we use bacteria to
  deal with NH3 NH4 and convert them to nitrate
  NO3

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The Nitrification Process

• Nitrification is a two step process
• Nitrosomonas bacteria convert ammonia (NH3) to
  Nitrite (toxic)
• Nitrobacter bacteria convert nitrite (NO2-)
• to nitrate (NO3) (virtually non-toxic)

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Nitrification Equation

• Nitrosomonas
• NH4 1.5 O2 ? 2 H NO2-
• Nitrobacter
• NO2- 0.5 O2 ? NO3

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The Take Home Message

• Bio-filtration is all about
• Surface area
• Living space for the bacteria
• Competition for that space
• Food (ammonia or nitrite
• Good living conditions
• O2 (enough), proper pH (6.8-7.5) and not to
  much CO2

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Lets Look at a Trickling Bio-filter
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The Filtration Done, Now Lets Renovate

• CO2 stripping
• CO2 is problematic in that it interferes with the
  biological processes of both fish and nitrifying
  bacteria
• CO2 is very volatile in water and can be stripped
  by mechanical agitation
• In the case of a trickling bio-filter the falling
  of
• water through the substrate, as well as, air
• diffusers in the bio-sump drive off unwanted CO2

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Aeration (addition of O2 to the system)

• Any type of aeration attempts to increase the
  surface contact area between the water and the
  gas
• The actual transfer occurs in a very thin area
  known as the water/ gas interface
• By increasing the surface area of that interface
  we can increase the amount of gas transfered

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Aeration Continued

• For a given volume of gas the smaller the bubble
  the better the exchange
• EXAMPLE
• A gas bubble with a diameter of 20 mm has a
  surface area of 12.6 cm3 and a volume of 4.19 cm3
  
• 296 3 mm bubbles could be made from the same 20
  mm bubble. The total surface area of these
  bubbles would be 83.6 cm resulting in an increase
  of almost 7 times the surface area!!!

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Oxygen Vs Air (with air stones)

• Airstones are very inefficient
• With air only 3-4 actually goes into solution
• Pure Oxygen with the best of airstones in 1m of
  water is better but only 30-40 efficient
• But we can do even better!!!!

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Down Flow Bubble Contactors Speece Cones
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How They Work

• Water is flows into the top of the contactor/
  cone
• Oxygen in injected near the top as well
• Water attempts to force the 02 down while the 02
  attempts to rise
• The result is a continuous contact between the
  gas and liquid with no loss to the atmosphere
• Oxygen Absorption efficiency 80-90!!!!
• Oxygen Transfer Efficiency 3.9 kg O2 / Kwh

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Water Flow from Biosump to Culture Tank
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Review The Whole Cycle