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