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Freshwater recirculation systems
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Recirculating system - 60%
• System components– solids filter– tanks– aeration
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Recirculating system 90%
• System components– solids filter– tanks– Aeration– Degasser (CO2)– biological filter– buffering systems
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Recirculating system 98%
• System components– solids filter– tanks– Aeration– Degasser (CO2)– biological filter– buffering systems– Anaerobic biofiltration– disinfection
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System Components
• Primary– Tanks– Solids filter– Biofilter– Aeration– Tanks
• Secondary – Pumps– Lighting– Disinfection
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Components of a Recirculating Aquaculture System continued
2. Biofiltration continued
Engineered forms:• Submerged•Fluidized beds• Emerged•Trickling/RBC•Combinations
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Solids Filtration
• Sources– Fish wastes– Uneaten food
• Types– Settable– Suspended– Fine and dissolved
Pressurized downflow sand filter
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Solids Filtration
• Settable solids (gravity removal)– Sediment trap– Settling tank– Hydrocyclone
(swirl separator)
Gravity SumpGravity Sump
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Solids Removal
• Suspended Solids (non-gravity)– Screen filtration– Expandable granular media
• Downflow (fine sand)• Upflow (course sand)
Screen filtersScreen filters
Screen
Suction
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Solids Filtration
• Fine and dissolved solids– Foam Fractionation
• Principle– Particles attach
to bubbles thatrise throughtube.
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Biological Filtration• Sources
– Fish metabolism
• Function– Nitrification
• Oxidizes ammonia and nitrite to nitrate
NONO33-- NHNH33
1½ O1½ O22
nitrosomonasnitrosomonas nitrobacternitrobacter
1½ O1½ O22 NONO22
--
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Types of Bio-filters
• Submerged filters– Simple– Inefficient
• Trickling filters– Simple– Aerates
Submerged filterSubmerged filter
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Oxygenation• Non-pressurized
• Downflow bubble contactor (DBC)• Counter current diffusion
column• U-tube diffusers
U-tubeU-tubeDBCDBC
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Degassing
• spray tower
• packed column
packed column
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Bicarbonate Drip• Rational
– CO2 removal (<20 mg/L)• from respiration
– Buffering• nitrification is an acidifying process
• Purpose– Adds alkalinity to water
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Recirculating Aquaculture System Components continued
2. Biofiltration continuedIdeal characteristics:• Large surface area: volume ratios•Long-lasting• Cheap•Light
KaldnesB-cell
198 m2/m3 152 m2/m3
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Recirculating Aquaculture System Components continued
2. Biofiltration continued
TAN
NO2
NO3
time (days)
mg
l- 1
0 40
15
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Particulate removal
Removal by:• Gravity separation•Filtration•Flotation
0.001 0.01 0.1 1 10 100 1000
supra colloidal
settleable
colloidal
dissolved
Particle size
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Particulate removal
10 25 50 75 100
fractionation
sedimentation
granular filters
microscreens
Particle size
cartridge filter
Optional treatment Main treatment Pretreatment
coarse screen
Most effective solids removal processes and particle range
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Recirculation systems
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Biological filtration
• Biological filtration is the use bacteria to removal of waste metabolites that accumulate from keeping, feeding and growing fish in a closed recirculating system.
• After oxygen, it is the accumulation of ammonia - the waste metabolite from protein digestion - that is probably the most limiting factor affecting the success of operating closed recirculation systems.
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Biological filtration• The removal of ammonia (NH3) by
oxidation to nitrite (NO2) and finally nitrate (NO3) is carried out by the bacteria Nitrosomonas sp. and Nitrobacter sp. respectively. This process is known as nitrification.
• Un-ionised ammonia and nitrite are both toxic to fish at relatively low concentrations whereas nitrate, the end product of nitrification, is relatively non-toxic at even quite high concentrations.
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Biological filtration
• The rate of nitrification is optimal around 30°C.
• The particular size and type of filtration equipment needed will depend on a number of factors including,
• the type of fish,
• the biomass of fish,
• the amount of food fed
• the temperature of the water.