Coldwater Biofilter Design Examples

1. Coldwater Biofilter Design Examples M.B. Timmons, Ph.D. Biological & Environmental Engineering Cornell University Ithaca, NY

2. Coldwater Design Example • Production Goal: 1.0 million lb/yr (454 mton/yr) • Arctic char

3. Large Operations Dominate Commercial Trout & Salmon Culture • Both culture technologies face tough environmental challenges. 6 m3/s flows to some farms 1,000-20,000 m3 per cage • There are few large water resources available for aquaculture development.

4. Large Production Systems are More Cost Effective • Economies of Scale • Reduce fixed costs per MTON produced • Reduce variable costs per MTON produced

5. 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)

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

7. 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

8. Oxygen Requirements • Estimate the mass and volume of oxygen required: • Account for oxygen transfer efficiency

9. 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

10. Flow Requirement • traditional trout culture rule of thumb • 50 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

11. Tank Volume Requirements • Assume an average fish density across all culture tanks in the system: • culture density = 60 kg fish/m3

12. 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.

13. Assuming 30 ft dia tanks water 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 tanks water depth 3.7 m 12 ft culture volume per tank 670 m3 177,000 gal 3-4 culture tanks required Tank Requirements

14. 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

15. 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.

16. 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

17. 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

18. 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.

19. Biofilter Sizing • Biofilter cross-sectional area can be calculated from the required flow rate (Q) and water velocity (v): Twelve biofilters that are each 11 ft dia (or other geometries could be used)

20. Static Sand Depth • Static sand depth can be calculated from the biofilter cross-sectional area (Q) and sand volume requirement:

21. Assume a Fully-Recirculating System (no water exchange) • Size biofilter to remove all of daily TAN production Example 2: Trickling Filter

22. Trickling Filter Sizing • The volume of packing required to remove the PTAN can be estimated using an areal TAN removal rate. TAN removal rate, g/d/m2 (Nitrification data at 15°C from Bovendeur. 1989.)

23. 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 (approximately $170,000 of ACCUPAC structured packing)

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

25. Trickling Filter • Packing depth can be calculated from the biofilter cross-sectional area (Abiof) and packing volume (Vpacking) requirement:

26. Trickling Filter • Must also design: • flow distribution manifold above packing • packing support structure • sump basin below packing to provide cleanouts and overflow back to pump sump • air inlet and outlet structures • Select air handler/fan to provide G:L = 5:1 (vol:vol)

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

28. Stripping Column Design • Design criteria used for the forced-ventilation cascade column: • volumetric G:L of 5:1 to 10:1 Each stripping columns will ventilate 3,630 scfm

29. Ozone Requirements • Estimate the ozone requirement of system’s feeding fish: • where: • aozone = kg ozone added per 100 kg feed

30. 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