Recirculating Aquaculture Systems Short Course Coldwater Biofilter Design Examples M.B. Timmons,...

Recirculating Aquaculture Systems Short Course

Coldwater Biofilter Coldwater Biofilter Design ExamplesDesign Examples

M.B. Timmons, M.B. Timmons, Ph.D.Ph.D.

Biological & Environmental Biological & Environmental EngineeringEngineering

Cornell UniversityCornell UniversityIthaca, NY Ithaca, NY


Coldwater Design Example

Production Goal: 1.0 million lb/yr (454 mton/yr)Arctic char


Large Operations Dominate Commercial Trout & Salmon Culture

Both culture technologies face tough environmental challenges.

There are few large water resources available for aquaculture development.

1,000-20,000 m3 per cage

6 m3/s flows to some farms


Large Production Systems are More Cost Effective

Economies of ScaleReduce fixed costs per MTON producedReduce variable costs per MTON produced


Design Assumptions

Assuming for the growout system:Mean feeding rate: F = 1.2% BW/day; Feed conversion rate: FCR = 1.3 kg feed/kg fish produced;

(these rates are an average over entire year)


System Biomass Estimation Estimate of system’s average feeding biomass :

systeminfishkg600,129

day365yr

feedkg2.1daysysteminfishkg100

producedfishkgfeedkg3.1

yrproducedkg000,454

r)FCR(productionannual

Biomassfeed

system


Oxygen Requirements Estimate the oxygen demand of system’s feeding fish:

where: RDO = average DO consumption rate

= kg DO consumed by fish per day (about 0.4)

aDO = average DO consumption proportionality constant

= kg DO consumed per 100 kg feed

day /consumed DO kg 622

feedkg 1DO kg 4.0

dayfish kg 100feed kg 2.1

fishkg600,129

arbiomassR DOfeedsystemDO


Oxygen Requirements Estimate the mass and volume of oxygen required:

Account for oxygen transfer efficiency

pliedsupOmin/L465 GasOofVolume 22

day /pliedsupgas O kg 890

%70100

dayconsumed DO kg 622

efficiencytransferO100

dayconsumed DO kg 622

GasOMass

2

22


Flow Requirements Estimate water flow (Q) required to meet fish O2 demand:

Assuming culture tank: DOinlet = 16 mg/L

DOeffluent= 9 mg/L (@ steady state)

DOsaturation = 10 mg/L

min)/gal320,16(min/L 700,61

min 1440day

mg 916L

kgmg 10

dayDO kg 622

DODO1

rQ

6effluentinlet

DO


Flow Requirement

traditional trout culture rule of thumb50 lb/yr production in 1 gpm of water flow (correct water

temp.) 76,000 L/min for 454 MTON/yr production 20,000 gal/min for 1 million lb (500 TON) annual production


Tank Volume Requirements Assume an average fish density across all culture

tanks in the system:culture density = 60 kg fish/m3

)gal000,570(m 160,2

fishkg60m1

fishkg600,129

DensityCultureBiomassVolumeCulture

3

3

system


Culture Tank Exchange Rate At a Q of 61.7 m3/min, the culture tank volume of 2160 m3

would be exchanged on average every 35 minutes .

Assuming ideal tank mixing.

min35m 7.61

minm160,2EXCH

33

ktan


Tank Requirements

Assuming 30 ft dia tankswater depth

2.3 m 7.5 ft

culture volume per tank 150 m3

40,000 gal

14-15 culture tanks required

Assuming 50 ft dia tankswater depth

3.7 m 12 ft

culture volume per tank 670 m3

177,000 gal

3-4 culture tanks required


Ammonia Production Estimate Calculate TAN production in system

where: RTAN = TAN production rate

= kg TAN produced by fish per day

aTAN = TAN production proportionality constant

= kg TAN produced per 100 kg feed

systemfeedTANTAN biomassraR

)%32(

/Produced 7.46

600,129 100

2.1

032.0

feedPAssumes

dayTANkg

fishkgdayfishkg

feedkg

feedkg

TANkgRTAN


Assume a Fully-Recirculating System (no water exchange)

Size biofilter to remove all of daily TAN production

Example 1: Fluidized-bed biofilters with fine sand, i.e., D10 = 0.2-0.25 m.


Biofilter Sizing The volume of static sand required to remove the

PTAN can be estimated using either volumetric or areal TAN removal rates:0.7 kg TAN removed per day per m3 static sand volume

3

3

sand static

m 67

TAN kg 7.0mday

dayTAN kg 7.46

V


Biofilter Sizing The volume of static sand required to remove the

PTAN can be estimated using either volumetric or areal TAN removal rates:0.06 g TAN removed per day per m2 bed surface area

(Sb) and Sb=11,500 m2/m3

3

2

323

sand static

m 67

m 500,11

mTAN g 06.0mday

kgg 10

dayTAN kg 7.46

V


Selecting a Sand for FSB

Select a fine graded filter sand that expands 50-100% at a velocity of 0.7-1.0 cm/s (10-15 gpm/ft2). a sand with D10=0.23 mm and a uniformity coefficient of

1.3-1.5 would expand about 50% at v = 1.0 cm/s.


Biofilter Sizing Biofilter cross-sectional area can be calculated from

the required flow rate (Q) and water velocity (v):

2

3biofilterbiofilter

m103

L 1000m

mcm100

cm 0.1sec

sec60min

minL700,61

v/QA

Twelve biofilters that are each 11 ft dia(or other geometries could be used)


Static Sand Depth Static sand depth can be calculated from the biofilter

cross-sectional area (Q) and sand volume requirement:

biofiltereachinsandstaticm

m

biofilersm

AreaVDepthSandStatic biofiltersand

0.1

8.8

12103

/

2

3


Assume a Fully-Recirculating System (no water exchange)

Size biofilter to remove all of daily TAN production

Example 2: Trickling Filter


Trickling Filter Sizing The volume of packing required to remove the PTAN can be

estimated using an areal TAN removal rate.T

AN

rem

ova

l ra

te, g

/d/m

2

(Nitrification data at 15°C from Bovendeur. 1989.)


Trickling Filter Sizing

The volume of packing required to remove the PTAN can be estimated using 0.25 g TAN removed per day per m2 bed surface area (Sb); Sb=200 m2/m3

3

2

323

packing

m 934

m 200

m

TAN g 25.0

mday

kg

g 10

day

TAN kg 7.46V

(approximately $170,000 of ACCUPAC structured packing)


Trickling Filter Biofilter cross-sectional area can be calculated from the

required flow rate (Q) and hydraulic loading rate (HLR=300 m3/day per m2):

2

3

23biofilterbiofilter

m296

m300

daym

day

min1440

min

m7.61

v/QA

Six biofilters that are each 7.0 m x 7.0 m (23 ft x 23 ft) square(or other geometries could be used)


Trickling Filter Packing depth can be calculated from the biofilter

cross-sectional area (Abiof) and packing volume (Vpacking) requirement:

biofiltereachindepthpackingm2.3

m296

m934

Area/VDepthPacking

2

3

biofilterpacking


Trickling Filter

Must also design:flow distribution manifold above packingpacking support structuresump basin below packing to provide cleanouts and

overflow back to pump sumpair inlet and outlet structures

Select air handler/fan to provide G:L = 5:1 (vol:vol)


Stripping Column Design Design criteria used for the forced-ventilation

cascade column:hydraulic fall of about 1.0-1.5 mhydraulic loading of 1.0-1.4 m3/min per m2

2

3

3

2

m 44

L 000,1m

m4.1

mminmin

L 700,61areaplan

Six stripping columns each with diameter = 3.0 m = 10 ft


Stripping Column Design Design criteria used for the forced-ventilation

cascade column:volumetric G:L of 5:1 to 10:1

scfm800,21min/m617

L 000,1m

waterL1airL10

minwaterL 700,61

flowair

3

3

Each stripping columns will ventilate 3,630 scfm


Ozone Requirements Estimate the ozone requirement of system’s

feeding fish:where:

aozone = kg ozone added per 100 kg feed

day /pliedsupozone kg 31

feedkg 100ozone kg 2

dayfish kg 100feed kg 2.1

fishkg600,129

arbiomassozonemass ozonefeedsystem


Overall Conclusions

Use appropriate level of intensification. Risk of failure higher for commercial reuse systems. Trends towards larger and more intensive reuse systems

for smolts and coldwater food-fish production: reduced capital costs per MTon produced reduced variable costs per MTon produced

especially labor and electric cost savings.

Technologies must scale functionally and cost effectively:certain technologies are better suited than others at large scales

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