Warm Water System
Design
James M. Ebeling,
Ph.D.
Research Engineer
Aquaculture Systems Technologies, LLC
New Orleans, LA
M.B. Timmons, Ph.D.
Biological & Environmental Engineering
Cornell University
Ithaca, NY
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Overview of System Design
Aeration
Air/Oxygen
Carbon Dioxide
Removal
Monitoring &
System Control
Disinfection
Fish Culture Tank
Fine & Dissolved
Solids Removal
5%
Sludge
Biosecurity
Program
Biofiltration
Nitrification
95%
Settable
Solids
Suspended
Solids
Sludge
Sludge
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Design Requirements
The Following Unit Process are required in any design:
• Culture Tank Design
• Circulation
• Solids Removal
• Biofiltration / Nitrification
• Gas Transfer (Aeration / Oxygenation / CO2 Removal)
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Design Assumptions
For any design, some
assumptions need to be made,
hopefully based either on
actual experience or reputable
research.
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Design Assumptions
Assuming: 454,000 kg/yr production (1 million pounds/year)
• Mean feeding rate: rfeed = 1.2% BW/day
• Feed conversion rate: FCR = 1.3 kg feed/kg fish produced
• Culture Density : 80 kg fish/m3
• Oxygen Demand: 0.75 kg O2/ kg feed
(these rates are an average over entire year)
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System Biomass Estimation
Estimate of system’s average feeding biomass :
Biomass system

annual production   ( FCR)

rfeed
454,000 kg fish / yr 1.3 kg feed / kg fish 1yr


(0.012 kg feed / day ) / kg fish
365 day
 129,600 kg fish in system / day
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Total Oxygen Requirements
• Estimate the oxygen demand of system’s feeding fish:
• where:
• RDO = average DO consumption Rate
= kg DO consumed by fish per day)
• aDO = average DO consumption proportionality constant
= kg DO consumed per 1 kg feed
Ranges from 0.4 to 1.0 kg O2/kg feed – cold water to warm water
RDO  biomass system  r feed  a DO
0.012 kg feed 0.75 kg DO
 129,600 kg fish 

kg fish  day
kg feed
 11,66 kg O2 consumed / day
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Total Flow Requirement – Oxygen Load
• Estimate water flow (Q) required for fish’s O2 demand:
• Assuming oxygen:
• DOinlet = 18 mg/L
• DOeffluent= 4 mg/L (@ steady state)
QTotal
1
 rDO 
DOinlet  DOeffluent 
1166 kg O2 106 mg
L
1




18  4 mg 1440 min/ day
day
kg
 57.84 m / min (15,280 gal / min)
3
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Total Tank Volume Requirements
Assume an average fish density across all culture tanks in
the system:
• culture density = 80 kg fish/m3
VolumeTotal  biomass system / Culture Density
129,600 kg fish

3
80 kg fish / m
 1,620 m3 (428,000 gal )
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Check Culture Tank Exchange Rate
EXCHTANK  VolumeTotal / QTotal
min
 1,620 m 
3
57.84 m
 28 min
3
Rule of Thumb
a culture tank exchange every 30-60
minutes provides good flushing of
waste metabolites while maintaining
hydraulics within circular culture tanks
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Number of Tanks Required
Assuming 9 m (30 ft) dia
tanks
Assuming 15 m (50 ft) dia
tanks
• water depth
• water depth
• 2.3 m
• 7.5 ft
• 3.7 m
• 12 ft
• culture volume per tank
• 150 m3
• 40,000 gal
• 10-11 culture tanks required
• culture volume per tank
• 670 m3
• 177,000 gal
• 2-3 culture tanks required
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Tanks Design Summary
Ten Production Tanks
• Diameter
9.14 m ( 30 ft )
• Water depth
• Flow Rate (30 min exchange)
5,000 Lpm (1,320gpm)
• Biomass Density
86 kg/m3 (0.72 lbs/gal)
2.3 m (7.5 ft)
• Culture volume per tank
150 m3 (40,000 gal)
• Oxygen Demand
117 kg O2/day (257 lbs/day)
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Solids Capture
Options for Solids Capture:
• Dual-drain System
• Settling Basin
• Swirl Separator
• Microscreen Filter
• Propeller Washed Bead Filter
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Solids Capture
One Options for Solids Capture:
Dual-drain System (15% bottom Drain)
Bottom Drain ▬►To a Swirl Separator
Combine Flow (Swirl Separator & Side-wall Drain)
▬► To
Microscreen Filter
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Biofiltration/Nitrification
Terms Used To Describe Biofilters:
• Void Space / porosity
• Cross-sectional Area
• Hydraulic Loading Rate
• Specific Surface Area
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Biofilter Design – Step 1
Step 1: Calculate the dissolved oxygen requirement (RDO).
Assume a DO consumption of 1.0 kg/kg feed
Both the MBB and Trickling Tower provide O2 for Nitrification
or approximately 0.25 kg. Thus 0.75 kg O2 /kg feed.
RDO  biomassTANK  rfeed  aDO
0.012 kg feed 0.75 kg DO
 12,960 kg fish 

kg fish  day
kg feed
 117 kg O2 consumed / day
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Biofilter Design – Step 2
Step 2: Calculate water flow requirement (Qtank) required for fish DO demand.
Assume:
DOinlet = 18 mg/L(pure oxygen aeration system)
DOtank = 4 mg/L (warm water 24 Deg. C, Tilapia!!)
QTANK
1
 rDO 
DOinlet  DOeffluent 
117 kg O2 106 mg
L
1




day
kg 18  4 mg 1440 min/ day
 5,800 L / min (1,530 gal / min)
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Biofilter Design – Step 2 (cont)
Step 2: Check the Exchange rate (2-4 exchanges/hr)
EXCHTANK  VolumeTANK / QTANK
150 m3

3
5.8 m / min
 26 min
A tank exchange rate of 2 exchanges per hour is OK!
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Biofilter Design – Step 3
Step 3: Calculate TAN production by fish (PTAN)
(Note: Feed is 35% protein)
PTAN = F * PC * 0.092 = F * 0.35 *0.092 = 0.032
where: PTAN = Production rate of total ammonia nitrogen, (kg/day)
F = Feed rate (kg/day)
PC = protein concentration in feed (decimal value)
PTAN  aTAN  Biomass TANK  rfeed
 0.032kg TAN / kg feed 12,960kg fish  0.012kg feed / kg fish
 5.0kg TAN
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Ammonia Assimilation Rates
Media Type
TAN Conversion
Basis
TAN Conversion
Rate
(15 to 20 Deg. C)
TAN Conversion
Rate
(25 to 30 Deg. C)
Trickling or RBC
(100 – 300 m2/m3)
Surface area of media
0.2 to 1.0 g/m2 day
1.0 to 2.0 g/m2 day
Granular
(bead/sand)
(> 500 m2/m3)
Volume of media
0.6 to 0.7 kg/m3 day
1.0 to 1.5 kg/m3 day
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Biofilter Design – Step 4 (MBB)
Step 4: Calculate volume of media, Vmedia based on the Volumetric
nitrification rate (VTR)
Consider a Moving Bed BioReactor (MBB)
Curler Advance X-1 has a 605 g TAN/m3 (17.14 g TAN/ft3).
PTAN
Vmedia 
VTR
5.0kg TAN

 8.23m 3
kg TAN
0.605
m3
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Biofilter Design – Step 4 (MBB)
Step 4: Calculate volume of biofilter, Vbiofiler based on a fill ratio of 65%.
Vmedia
Vbiofilter 
Fill %
8.23m3

 12.66m3
0.65
This would require a tank (3200 gal): 7 ft in diameter and 11 ft tall.
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Biofilter Design – Step 4 (Trickling Tower)
Step 4: Calculate the surface area (Amedia) required to remove PTAN from
the Areal TAN removal rate (ATR) (0.45 g TAN/m2 day)
PTAN
Amedia 
ATR
kg
1,000 g
5.0 TAN 
day
kg

 11,100m 2
0.45 gTAN
m 2 day
2
10
.
76
ft
2
11,100m 2 

120,000
ft
m2
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Biofilter Design – Step 5 (Trickling Tower)
Step 5: Calculate volume of media based on the specific surface area
(SSA), example BioBlock = 200 m2/m3 (61 ft2/ft3)
Amedia
Vmedia 
SSA
11,100 m 2
3


55
.
5
m
m2
200 3
m
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Biofilter Design – Step 6 (Trickling Tower)
Step 6: Calculate the biofilter cross-sectional area from required flow for
the fish oxygen demand (Qtank) and the hydraulic loading rate, HLR of
250 m3/m2 day (4.4 gpm/ft2).
Qtank
Abed 
HLR
L
1m3
1
1,440 min
 5800



3
min 1,000 L 250m
day
2
m
2
2
 33.4 m  360 ft
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Biofilter Design – Step 7 (Trickling Tower)
From high school math class:
area =  (Dia)2 / 4
diameter = [ 4 * area / ]1/2
The diameter of a two trickling towers, Dbiofilter, with this cross sectional area is:
4  Abed
4 16.7m 2
Dbiofilter 

 4.61m  15 ft

3.14
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Biofilter Design – Step 8 (Trickling Tower)
Step 8: Calculate the biofilter depth (Depthmedia) from
the biofilter cross-sectional area (Amedia) and volume (Vmedia).
Vmedia 16.7m3
Depthmedia 

 3.62m  11.9 ft
2
Amedia 4.61m
The final Trickling Tower is
15 ft in diameter
and 12 ft tall
plus distribution plate, etc.
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Aeration / Oxygenation Options
Multi-staged low head oxygenators (LHO)
Packed or spray columns
Pressurized columns
Enclosed mechanical surface mixers
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Tank Oxygen Requirements
• Estimate the oxygen demand of system:
• where:
• RDO = average DO consumption Rate
•
= kg DO consumed by fish per day)
• aDO = average DO consumption proportionality constant
•
= kg DO consumed per 1 kg feed
• Ranges from 0.4 to 1.0 kg O2/kg feed – cold water to warm water
RDO  biomassTANK  rfeed  a DO
0.012 kg feed 0.75 kg DO
 12,960 kg fish 

kg fish  day
kg feed
 117 kg O2 consumed / day
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Tank Oxygen - Speece Cones
(Design Requirement: 117 kg O2 / day or 4.88 kg / hr)
From Aquatic Eco-Systems, Inc. Catalog:
A single Speece Cone:
OY140F is rated at: 4.5 kg O2 /hr @ 10 psi, 600 gpm, 40 mg/L
Or two Speece Cones:
OY60F is rated at 2.3 kg O2 /hr @ 15 psi, 260 gpm, 46 mg/L
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CO2 PRODUCTION
• Molar basis
• 1 mole of CO2 is produced for every
1 mole O2 consumed
• Mass basis
• 1.38 g of CO2 is produced for every
1 g O2 consumed
RCO2  biomassTANK  rfeed  aDO 1.38 g CO2 / g O2
0.012 kg feed 0.75 kg DO
 12,960 kg fish 

1.38 g CO2 / g O2
kg fish  day
kg feed
 161.5 kg CO2 produced / day
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CO2 Control Options
•
•
•
•
•
•
•
Packed Tower Stripping
Sodium Hydroxide Addition
Water Exchange
In-tank Surface Aeration
Side-stream Surface Aeration
In-tank Diffused Aeration
Side-stream Diffused Aeration
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Stripping Column Design
• Design criteria used for the forced-ventilation
cascade column:
• hydraulic fall of about 1.0-1.5 m
• hydraulic loading of 1.0-1.4 m3/min per m2
plan area
5,000 L min  m 2
m3



3
min
1.4 m 1,000 L

3.6 m 2  38.4 ft 2
one stripping columns with diameter = 2.0 m = 6.6 ft
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Stripping Column Design
• Design criteria used for the forced-ventilation
cascade column:
• volumetric G:L of 5:1 to 10:1
air flow
5,000 L water 10 L air
m3



min
1 L water 1,000 L

50 m3 / min  1,770 scfm
Fan requirement: 1770 scfm
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Ozone Requirements
• Estimate the ozone requirement of system’s
feeding fish:
• where:
• aozone = kg ozone added per 100 kg feed
mass ozone  biomass system  rfeed  aozone
1.2 kg feed
2 kg ozone
 12,900 kg fish 

100 kg fish  day 100 kg feed
 3.1 kg ozone supplied / day
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Putting It All Together
Aeration
Air/Oxygen
Carbon Dioxide
Removal
Disinfection
Fish Culture Tank
Fine & Dissolved
Solids Removal
Biofiltration
Nitrification
Sludge
Monitoring &
System Control
Waste Solids
Removal
Sludge
Recirculating Aquaculture Systems Short Course