1. Biofilter Decisions Daniel Miller dmille31@wvu.edu
Florida A&M University
Farmer to Farmer Program
Stellenbosch, South Africa
Feb. 2010

2. Objectives After participating in this discussion you will be able to:
Determine the amount of biofiltration (size) required for a given recirculating system.
Predict daily ammonia production.
Speak the language (of engineers)
List and describe 3 types of waste
List and describe 3 types of water treatment
Describe 3 types of biofilters
Discuss how to minimize waste.

3. Questions to determine biofilter size
How much high quality commercial feed / day?
What is the protein level of the feed?
How much surface area is needed for biofilter?
How much volume is available?
What is the operating temperature (max/min)?
What type of media will be used?
What is the daily NH4 conversion rate of the media?

4. Biofilter Terminology
Specific surface area: (m²/m³) is the area the nitrifying bacteria has available per unit of volume.
Hydraulic loading rate: (m³/m²/day) is the volume of water moving through a biofilter per unit of cross-sectional area per day.
Void space: is the % volume of biofilter not occupied by media

5. Fluidized bed sand filter
Fluidized bed sand filter: Fluidized bed biofilters are simple, extremely compact, self-cleaning, quiet and easy to use. very high surface area : volume ratio (good)
TIP: Should be designed by an engineer.
Requires careful selection of sand size to avoid blowout of particles, which become lighter with biofloc attachment.

6. Trickle filter Removes carbon dioxide Increases oxygen
Specific Surface area:
100 to 300 m²/m³
Low efficiency in cool water
Open at top & bottom
Works well in low loads with variable feeding rates.

7. Rotating biological contactor (RBC)
Air or water can rotate the media
Self cleaning
Minimal hydraulic head to operate
Specific Surface area: 250 m²/m³
Can become very heavy with time.
Rotation: 1.5 to 2.0 per minute
Adds oxygen and removes CO2

8. Ammonia conversion rates are greatly influenced by temp*.
Fluidized bed sand filter: Volume of media (m³)
m²/m³
<20C = 0.65 kg/m³/day
>25C = 1.25 kg/m³/day
Trickle filter:
Surface area of media
m²/m³
15-20C g/m²/day
>25C g/m²/day
* Timmons and Ebling (2007) Recirculating Aquaculture

9. EXAMPLE - 1
Water temp: 15C Max. feeding rate 172 kg/day (42p/20f : high quality pellet) Biofilter : Trickle filter Biomedia: 245 m²/m³ Conversion rate: 0.20 g/m²/day* 172 kg feed/day (x 3%) = 5.16 kg NH3 1 exchange per 4 days (new water) = 4 kg NH3

10. CALCULATIONS -1 4.0 kg NH3 will require how much nitrification area?
Divide by kg NH3/m²/day
Result: 20,000 m² of surface area.
Divide by 245 m²/m³ = 81.6 m³ of biofilter

11. EXAMPLE - 2
Water temp: 15C Max. feeding rate 172 kg/day (42p/20f : high quality pellet) Biofilter : Fluidized bed sand filter Biomedia: sand (graded) Conversion rate: 0.6 kg/m³/day 172 kg feed/day (x 3%) = 5.16 kg NH3 1 exchange per 4 days (new water) = 4 kg NH3

12. CALCULATIONS - 2 4.0 kg NH3 will require how much volume?
Divide by 0.6 kg/m³/day = 6.6 m³ of sand
Compare efficiencies per volume:
81.6 m³ versus 6.6 m³ shows that the fluidized bed sand filter is 12.3 times more efficient per unit area than the trickle filter at 15 degrees C.

13. Production losses / Growth loss occurs when:
Oxygen levels drop below 5 mg/l (ppm)
CO2 levels exceed 25 mg/l (ppm)
Ammonia levels exceed 0.03 mg/l (ppm)
Solids are not removed from system quickly
Biofilter media becomes clogged.

14. Wastewater Treatment Options
Primary (settleable solid removal)
Settling ponds (large particles)
Sediment traps
Microscreens (>60 microns)
Filters: drum, bead, sand ,
Secondary (suspended / dissolved waste removal)
Foam Fractionators (<30 microns)
Constructed wetlands
Hydroponics (SRAC # 454)

15. Wastewater Treatment Options
Tertiary (pathogen removal)
Chlorine and sodium thiosulfate (removes Cl-)
Ozone
Ultraviolet radiation (UV)

16. Waste Minimization in Aquaculture is critical and economical
Choose high energy extruded formulas for feed.
Good Feed handling and feeding practices.
Design factors – for rapid concentration and removal of solid waste.
Hand feed and other methods work well.

17. How do you minimize waste?
Research shows that high energy feeds (42% protein, 20% fat) can reduce solid waste versus the standard ration (38:12).
The “extrusion” process pre-cooks the feed to allow for higher absorption and lower amounts of solid waste, buy high energy extruded feeds.
Routinely check feeders for proper adjustment. Hand feed carefully, record daily feed used.
Design for best water flow (settle-concentrate-remove solids)
Handle feed bags with care.

18. Forms of Waste Metabolic Waste (solid and dissolved)
Chemical Waste (dissolved)
Pathogenic Waste (biological)
Dissolved Waste: phosphorus, BOD, COD, nitrogenous waste is toxic to fish (NH3, N02) Each of these are a result of feed inputs.
Solid Waste: fish, feces, algae, & bacteria will contribute to dissolved waste. By reducing solid waste, dissolved waste will also be reduced.

19. Metabolic Waste: dissolved /suspended
Approximately 30% of the feed will become solid waste. Avoid pumping solid waste!
Quick concentration and removal from system is required (design, flow control).
Good feed handling, storage, and routine on farm will reduce “dust particles”.
Size of waste matters: fragmentation causes leaching of nutrients and increases settling rate. Avoid pumping solid waste!

20. Cornell-type dual drain For rapid concentration and removal of solids
Low volume (5%)– High solids center drain
High volume (95%) – Low solids side drain

22. How to Dispose of Waste? Permitted Land Application
Composting: Combine with wood chips or saw dust to attain a C:N ratio of 30:1
Requires aeration, layering, monitoring with thermometer (60 C for 3-4 days)
Constructed Wetlands (dissolved waste)
Neutralize pathogens with ozone, chlorine, or ultraviolet radiation (UV).

23. Denitrification in Recirculating systems
Removing nitrate (NO3) to N (gas)
Technology is improving
Consult a bio-engineer for
design limits.
Used for sensitive species