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 Pro’s and Con’s
Less water needed
Less land needed
Temperature Control
Water Quality Control
Waste Retention
Better feed Conversion
Product Isolation
Inventory Control
CON’S
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
Feed’s Impact On Water Quality Is Almost Always NEGATIVE Inputs 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) > 6.0*
Carbon Dioxide ( CO2 )(mg/l) < 20 pH
Alkalinity (mg/l)
Ammonia (NH3) (mg/l)
Nitrite (NO2)(mg/l)
Nitrate (NO3) <1000
*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
Kg CO2
Kg Waste Solids (dry weight)
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 3:1
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
Vs< 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:
NH O2  2 H+ + NO2-
Nitrobacter:
NO 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 ( ) and not to much CO2

23. Lets Look at a Trickling Bio-filter

24. The Filtration Done, Now Let’s 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 % 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