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Bowling Green Satellite Aquaculture Center

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Bowling Green Satellite Aquaculture Center Introduction to Recirculating Aquaculture Workshop Critical Considerations in Recirculating Production Systems Definition ... – PowerPoint PPT presentation

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Title: Bowling Green Satellite Aquaculture Center


1
Bowling Green Satellite Aquaculture Center

Introduction to Recirculating Aquaculture
Workshop
2
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)

3
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

4
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!!!

5
Feed Effects on Water Quality
  • Feeds Impact On Water Quality Is Almost Always
    NEGATIVEInputs and Outputs Based on the Input
    of 1Kg of Feed

6
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

7
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

8
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

9
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

10
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!

11
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

12
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!!!!

13
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

14
  • Flow A 85-90 of flow
  • Flow B 15-20 of flow

15
So we have removed the solids from the tank ! Now
what?
  • Suspended Solids
  • One of the most effect methods
  • Drum Screen filtration

16
Drum Screen Operation
17
Settleable Solids
  • 15 of flow
  • Referred to as a swirl separator or hydrocyclone
  • Discharge from SS re-enters flow to drum screen
    filter

18
Lets look at it all together
19
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

20
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)

21
Nitrification Equation
  • Nitrosomonas
  • NH4 1.5 O2 ? 2 H NO2-
  • Nitrobacter
  • NO2- 0.5 O2 ? NO3

22
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

23
Lets Look at a Trickling Bio-filter
24
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

25
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

26
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!!!

27
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!!!!

28
Down Flow Bubble Contactors Speece Cones
29
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

30
Water Flow from Biosump to Culture Tank
31
Review The Whole Cycle
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