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Bowling Green Satellite Aquaculture Center

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 pass120% exchange per day Closed system0-20% volume change per day (typical of systems being designed today).

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Bowling Green Satellite Aquaculture Center

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    1. Bowling Green Satellite Aquaculture Center

    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 PRO’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 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) <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 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 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: 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 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 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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