Aq2010 0875 tilapia

Research on Biofloc Tank Culture of Tilapia James Rakocy, Donald Bailey, Charlie Shultz and Jason Danaher University of the Virgin Islands Agricultural Experiment Station

Objectives the production of tilapia in a 200-m3 tank employing aeration, solids removal, mixing, bacterial-based treatment in the water column, and denitrification. ď ľ Modify and improve the system during the course of four production trials. ď ľ Evaluate

Initial Tank Design 200 m3, 16 m diameter, 1 m mean water depth  Surface area: 200 m2 (0.02 ha or 1/20 acre)  Bottom: 3o slope to center  Center clarifier: 1 m3, 45o slope, fiberglass, 10-cm drain  Outside standpipe for solids removal  Aeration: three ¾-hp Kasco aerators  Water movement: one ¾-hp Kasco aerator angled  Size:

Biofloc Tank

16 m 1.09 m

Total Culture Volume = 200 m3

0.15 m Freeboard

3ยบ Slope Sludge Cone Volume = 1.0 m3 Sludge Removal Line

Biofloc Tank Aeration device Central cone

Base addition tank

Drain Flow

Sludge collection and measurement To storage lagoon

Procedures  Aeration

continuously  Mix continuously to maintain suspension of biofloc  Remove settleable solid waste daily  Feed twice daily with floating feed (32% protein)  Feed ad libitum for 30 – 40 minutes  Monitor pH, maintain pH 7.5 with Ca(OH)2  Add CaCl2 to prevent nitrite toxicity  Monitor important water quality parameters

Trial 1 rate: 20 fish/m3 ď ľ Solids removed from central cone ď ľ Stocking

Production Trial

1 2 3 4

Stocking Initial Size (g) Rate (#/m3) 20

214

Final Size (g) 912

Culture Growth Final FCR Survival Period Rate Biomass (%) (d) (g/d) (kg/m3) 175

4.0

14.4

2.2

78.9

Trial 2 rate: 25 fish/m3  Solids removed from central cone  In last 3 weeks solids also removed by external clarifier  Stocking

Clarifier Efficiency

Clarifier effluent Culture tank water Sludge from clarifier

After 10 minutes of settling

Total Suspended Solids 2000 1500 Trial2 1000 500

Week

28

26

24

22

20

18

16

14

12

10

8

6

4

2

0

0

Concentration (mg/L)

2500

Production Trial

Stocking Initial Size (g) Rate (#/m3)

Final Size (g)

Culture Growth Final FCR Survival Period Rate Biomass (%) (d) (g/d) (kg/m3)

1

20

214

912

175

4.0

14.4

2.2

78.9

2

25

73.6

678

201

3.0

13.7

1.9

81.0

3 4

Trial 3  Solids

removed solely by external claifier  Denitrification tank employed  Bird netting at edge of tank

Biofloc Tank Trial 3

Aeration devices

Base addition tank Pump

Flow Horizontal mixer

Clarifier

Sludge removal to storage lagoon

Nitrate-Nitrogen – Trial 1 - 3 800 Trial 1 Trial 2 Trial 3

Concentration (mg/L)

700 600 500 400 300 200 100 0 1

3

5

7

9

11

13

15 Week

17

19

21

23

25

27

29

TSS – Trial 2 and 3 2500 Trial 2

2000

mg/L

Trial 3 1500 1000 500 0 0

5

10

15 Week

20

25

30

Production Trial

Stocking Initial Size (g) Rate (#/m3)

Final Size (g)

Culture Growth Final FCR Survival Period Rate Biomass (%) (d) (g/d) (kg/m3)

1

20

214

912

175

4.0

14.4

2.2

78.9

2

25

73.6

678

201

3.0

13.7

1.9

81.0

3

25

70.0

707

182

3.5

15.3

1.8

86.0

4

Trial 4 ď ľ Complete

bird netting barrier

Production Trial

Stocking Initial Size (g) Rate (#/m3)

Final Size (g)

Culture Growth Final FCR Survival Period Rate Biomass (%) (d) (g/d) (kg/m3)

1

20

214

912

175

4.0

14.4

2.2

78.9

2

25

73.6

678

201

3.0

13.7

1.9

81.0

3

25

70.0

707

182

3.5

15.3

1.8

86.0

4

25

154

745

183

3.2

18.6

2.0

99.7

Major Inputs and Outputs Trial

Initial Water (m3)

Makeup Water (L/day)

Sludge (L/d)

Feed (kg/day)

Base Addition (kg/day)

Electricity (kWh/day)

1

200

880

470

25.4

1.5

52.8

2

200

401

366

23.0

1.7

52.8

3

200

588

213

27.3

0.9

58.9

4

200

577

240

33.0

1.3

71.7

Water Quality Parameter (mg/L)

Trial 1 Mean 5.5

Trial 2 Mean 7.9

Trial 3 Mean 5.3

Trial 4 Mean 5.3

Water Temp (C)

26.8

28.5

26.1

26.4

NH3-N

1.2

1.8

2.0

2.3

NO2-N

1.5

2.7

1.9

5.6

pH

7.8

7.8

7.7

7.5

Total Alkalinity

224

204

247

211

DO

Water Quality Parameter (mg/L) Chlorophyll a (ug/L) COD Settleable solids (ml/L) TSS Ortho-Phosphate Cl

Trial 1 Mean 1895 353 29 476 16.9 301

Trial 2 Mean 924 363 48 855 19.2 317

Trial 3 Mean 820 292 23 317 34 95

Trial 4 Mean 937 315 10 368 32 370

Concentration (mg/L)

Total Ammonia-Nitrogen – Trial 1 - 4 10 9 8 7 6 5 4 3 2 1 0

Trial 1 Trial 2 Trial 3 Trial 4

0

5

10

15 Week

20

25

30

concentration (mg/L)

Nitrite-Nitrogen – Trial 1 - 4 20 18 16 14 12 10 8 6 4 2 0

Trial 1 Trial 2 Trial 3 Trial 4

0

5

10

15 Week

20

25

30

Biofloc Culture Advantages  Simple

management  Low water requirements  Algal die-offs do not cause mortality  Algae and bacteria supplement tilapia diet  No off-flavor detected  Production ~ 37 times higher than ponds for tilapia  No recruitment problem  Wastewater used to irrigate and fertilize field crops or return to the system  Solid waste used as soil amendment and potting mix

Biofloc Culture Disadvantages  Requires

a 6-week period to establish bacterial populations  Suspended solids nitrification less stable than fixedfilm nitrification  Feeding response fluctuates  Algal die-off reduces feeding response temporarily  High energy input  Reliance on continual aeration and mixing requires backup power

Key Results  Total

tilapia production: (3711 kg in 1/50-ha tank) or (8,163 lbs in 1/20-acre tank)  Potential from trial 4 of 16,326 lbs per year in 1/20-acre tank  Daily makeup water averaged 0.29% (0.58 m3) of total water volume  Recovered approximately 40% (0.23 m3) of daily makeup water.

Conclusions  This

biofloc system was 37 times more productive than a standard earthen pond (18.6 vs. 0.5 kg/m3)  External clarification simplifies tank construction, improves solids removal and water quality and increases production  Simple open channels with solids accumulation can provide adequate denitrification  This production technology conserves water and land by 97% and recovers solids and nutrients.  All waste products of system can be reused.

Future Research (1,000 m2?, 4,000 m2?)  Aeration requirement  Mixing technique  Reduce energy costs  Solids removal  Return Geotube® filtrate to system  Species  Economics  Scaleup