Transcript Biofilter Decisions - West Virginia University

Biofilter Decisions
Daniel Miller
[email protected]
Florida A&M University
Farmer to Farmer Program
Stellenbosch, South Africa
Feb. 2010
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.
Questions to determine biofilter size
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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?
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
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.
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.
Rotating biological contactor (RBC)
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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
Ammonia conversion rates are greatly
influenced by temp*.
Fluidized bed sand filter:
Volume of media (m³)
500 - 800 m²/m³
Trickle filter:
Surface area of media
100 - 300 m²/m³
• <20C = 0.65 kg/m³/day
• >25C = 1.25 kg/m³/day
• 15-20C 0.2-1.0 g/m²/day
• >25C 1.0- 2.0 g/m²/day
* Timmons and Ebling (2007) Recirculating Aquaculture
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
CALCULATIONS -1
• 4.0 kg NH3 will require how much nitrification
area?
• Divide by 0.0002 kg NH3/m²/day
• Result: 20,000 m² of surface area.
• Divide by 245 m²/m³ = 81.6 m³ of biofilter
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
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.
Production losses / Growth loss occurs
when:
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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.
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)
Wastewater Treatment Options
Tertiary (pathogen removal)
• Chlorine and sodium thiosulfate (removes Cl-)
• Ozone
• Ultraviolet radiation (UV)
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.
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.
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.
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!
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
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).
Denitrification in Recirculating systems
Removing nitrate (NO3) to N (gas)
Technology is improving
Consult a bio-engineer for
design limits.
Used for sensitive species