Biofilter Decisions Daniel Miller dmille31@wvu.edu 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 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) 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 <20C = 0.65 kg/m³/day >25C = 1.25 kg/m³/day Trickle filter: Surface area of media 100 - 300 m²/m³ 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: 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