SLIDE 1 Intensive Tank Culture of Tilapia with a Suspended, Bacterial-Based, Treatment Process
James Rakocy, Donald Bailey, Eric Thoman and Charlie Shultz
University of the Virgin Islands Agricultural Experiment Station
- St. Croix, U.S. Virgin Islands
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Tank Dimensions and Characteristics
Size: 200 m3, 16 m diameter, 1 m mean water depth Block wall and 30 mil HDPE liner 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 vertical-lift aerators Water movement: one ¾-hp vertical-lift aerator tilted horizontally
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Tank Design
16 m Sludge Cone Volume = 1.0 m3 1.09 m 0.15 m Freeboard Total Culture Volume = 200 m3 Sludge Removal Line 3º Slope
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Tank Plan View
To storage lagoo Flow Base addition tank Central cone Drain Aeration device Sludge collection and measurement
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Treatment Processes and Production Management
Continuous aeration Mixing to maintain suspension of bacterial floc Nitrification in water column Settleable solid waste removal once daily Feed twice daily with floating feed (32% protein) Feed ad libitum for 30 – 60 minutes Monitor pH daily, maintain pH 7.5 with Ca(OH)2 Add CaCl2 to prevent nitrite toxicity
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Production
81.0 1.9 13.7 3.0 201 678 73.6 25 2 78.9 2.2 14.4 4.0 175 912 214 20 1 Surviva (%) FCR Final Biomass (kg/m3) Growth Rate (g/d) Culture Period (d) Final Size (g) Initial Size (g) Stocking Rate (#/m3) Trial
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Major Inputs and Outputs
2 1 Trial 52.8 1.5 25.4 470 880 200 23.0 Feed (kg/day) 52.8 1.7 366 401 200 Electricity (kWh/day) Base Addition (kg/day) Sludge (L/d) Makeup Water (L/day) Initial Water (m3)
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Water Quality
Trial 2 Mean Trial 1 Mean Parameter (mg/L) 204 7.8 2.7 1.8 28.5 7.9 224 Total Alkalinity 7.8 pH 1.5 NO2-N 1.2 NH3-N 26.8 Water Temp (C) 5.5 DO
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Water Quality
Trial 2 Mean Trial 1 Mean Parameter (mg/L) 317 19.2 855 48 363 924 301 Cl 16.9 Ortho-Phosphate 476 TSS 29 Settleable solids (ml/L) 353 COD 1895 Chlorophyll a (ug/L)
SLIDE 23 Total Ammonia Nitrogen – Trial 1 & 2
1 2 3 4 5 6 7 8 9 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 Week Concentration (mg/L) Trial 1 Trial 2
SLIDE 24 Nitrite Nitrogen – Trial 1 & 2
2 4 6 8 10 12 14 16 18 20 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 Week Concentration (mg/L) Trial 1 Trial 2
SLIDE 25 Nitrate Nitrogen – Trial 1 & 2
100 200 300 400 500 600 700 800 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 Week Concentration (mg/L) Trial 1 Trial 2
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SLIDE 27 Feed – Trial 1
10 20 30 40 50
14 28 42 56 70 84 98 112 126 140 154 168
Day Feed (kg) kg Feed
SLIDE 28 Feed – Trial 2
10 20 30 40 50 1 29 57 85 113 141 169 197 Date
Feed (kgs)
SLIDE 29 Sludge – Trial 1
1000 2000 3000 4000 5000 6000 7000 14 28 42 56 70 84 98 112 126 140 154 168 Day Liters (L)
Liters
SLIDE 30 Total Suspended Solids Settling Curve
500 1000 1500 2000 5 10 15 20 25 30 Time (min) TSS (mg/L) Trial 1 Trial 2
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Clarifier effluent Culture tank water Sludge from clarifier After 10 minutes of settling
Clarifier Efficiency
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88.5 Removal (%) 26,230 Sludge TSS (mg/L) 136 Effluent TSS (mg/L) 1178 Influent TSS (mg/L)
External Clarifier Efficiency
SLIDE 37 Sludge – Trial 2
500 1000 1500 2000 2500 3000 3500 4000 4500 1 29 57 85 113 141 169 197 Day Sludge removed (L) Sludge removed
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Day 7-21 Day 1-6 2.5 3.3 Cone (%) 97.5 96.7 Clarifier (%) Percentage 0.3 1.0 Mean (kg/d) 4.8 5.9 Total (kg) Cone 12.3 29.2 Mean (kg/d) 184.4 175.5 Total (kg) Clarifier
Sludge Removal
SLIDE 39 Total Suspended Solids
500 1000 1500 2000 2500 2 4 6 8 1 1 2 1 4 1 6 1 8 2 2 2 2 4 2 6 2 8 Week Concentration (mg/L) Trial2
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Advantages of Bacterial-Based Tank Culture
Simple management Low water requirements Seepage problems avoided Not affected by algal die-offs Algae and bacteria supplement tilapia diet No off-flavor detected Production ~ 30 times higher than ponds No recruitment problem Wastewater used to irrigate and fertilize field crops
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Disadvantages of Bacterial-Based Tank Culture
Feeding response fluctuates Suspended solids nitrification less stable than fixed-film nitrification High energy input
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Key Results
Total tilapia production: 2,740 – 2,880 kg in a 0.02-ha tank Daily makeup water averaged 0.20 - 0.43% of total volume: 0.40-0.86 m3 Recovered approximately 0.38 m3 of water daily for irrigation and fertilization of field crops.
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Future Research
Scale-up (1,000 m2?, 4,000 m2?) Aeration requirement Size and number of clarifiers Species Economics
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Conclusions
A simple tank construction method was developed The tank was nearly 30 times more productive than a standard earthen pond (13.7 and 14.4 vs. 0.5 kg/m3) External clarifier simplifies construction, improves solids removal and water quality and may increase production This production technology conserves water and recovers solids and nutrients
