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BMPs for Aquaculture Production Lori Marsh, Associate Professor, Biological Systems Engineering, Virginia Tech September 19, 2005
Aquatic Animal Production (CAAP/AAP) Systems: • • • Flow-through Recirculating Net pen and cages Ponds Lobster pounds, Crawfish, Shellfish, Aquariums, and Alligators
Flow-through Systems • • • Constantly flowing culture water Commonly use raceways or tanks Found throughout US Require consistent volume of water Most use well, spring or stream water as source • Primary method to grow salmonid species such as rainbow trout.
Recirculating Systems • Highly intensive culture • Actively filter and reuse water • Water treatment including – Ammonia removal – Solids removal – Oxygenation – Temperature control…. • Capital intensive at startup
Net Pens and Cages • Suspended or floating holding systems • Located along a shoreline or pier or anchored off shore • Rely on natural water movement to assure water exchange/quality for fish
What’s the Problem with CAAPs? • 4, 200 commercial facilities (1998 USDA census) • Water quality concerns include – Suspended solids, P, NH 3, BOD – Drugs (e. g. oxytetracycline or formalin) – Chemicals (e. g. copper-containing pesticides) – Pathogens (primarily a concern for native biota)
BMPs for Feed Management • • • Applicable to all systems Avoid overfeeding Match feeding to feed requirements Direct feed to fish Use quality feed, and store to reserve nutrient quality • Handle feed to minimize fines • Active feed monitoring (net pens): detects when feed pellets are passing below fish.
BMP for Removal of Solids in a Flow-through System • Quiescent Zones typically constructed with wire mesh to exclude fish from last 10% of raceway. • Designed to insure that overflow rate is smaller than particle settling velocity. • Solids typically removed by suction through a vacuum head.
Other BMPs for Solids Removal • Sedimentation basins – Off-line settling (OLS) basins receive water and solids slurry from Quiescent Zone (QZ). • Note: QZ + OLS are most common settling system for flowthrough systems. – Full-flow settling (FFS) systems stand alone and collect water flow from entire facility (need 2 operating in parallel for solids removal). • Secondary Settling – Microscreens – Vegetated ditches – Constructed wetlands
Solids Disposal • Dewatering – Natural evaporation – Mechanical assistance • • • Filtration Squeezing Capillary action Vacuum withdrawal Centrifugal – Chemicals are often added to assist with the dewatering process
Solids Composting • Dewatered sludge mixed with bulking agent to add carbon, reduce moisture, increase aeration • Must be aerated (turned or by adding air) • Often screened to remove bulking agent – Advantages: reduces volume, stabilizes material, heating destroys pathogens, value added product
Vermicomposting of solids VERMICOMPOST WORMS Vermicomposting uses earthworms to transform organic wastes and results in two saleable products: vermicompost and worms.
WHY CONSIDER VERMICOMPOSTING? Two saleable products Possibility of worms as fish feed Worm composting faster than microbial Worms turn the material so machines/people don’t have to Vermicomposting suitable for highmoisture waste
HYDROCLONE After settling, the contents were run through a hydroclone.
WORM BINS The bins in operation
WORM SEPARATOR Material from beds was run through a trommel screen resulting in screened material, unscreened compost, and worms.
CONCLUSIONS Processing rate very slow during extreme temperature conditions >29 C or < 10 C; therefore an unconditioned greenhouse does not appear suitable for this process. During more optimum temperature conditions, worms processed 2. 3 kg dry sludge/m 2 -week. For the estimated sludge production at BRA, a 30. 5 m x 91. 5 m (100’x 300’) structure would be required to house sufficient worm beds.
Land Application of Solids • Can land apply without dewatering – Hydraulic limitations not nutrient • Need provisions for times of frozen ground • BMPs for land application of animal wastes would apply, e. g. site conditions, weather, crop nutrient uptake, application rates, land availability, setbacks, slopes, neighbors, etc.
Waste Treatment Options for Effluent • POTW • Lagoons: BMPs for lagoons apply, e. g. site selection, design, start up, maintenance, record keeping, clean water diversion, etc.
Mortality Management • Avoid disease outbreaks • Inspect daily, remove mortality promptly • Proper disposal—composting, rendering
BMPs for Ponds • Avoid discharges e. g. seine harvest rather than draining; maintain freeboard for storm volume, drain from top when necessary. • Implement erosion control for pond ( protection from waves, aerators, vehicles, etc. ) and watershed. • Manage rainwater: divert excess runoff, • Maintain good vegetation and avoid livestock production in watershed. • Use drugs and chemicals only as needed, use only FDAand EPA-approved water quality enhancers and follow label directions carefully.
Constituents of concern • Nutrients • Bacteria (? ) – Carr, O. J. and R. Goulder. 1993. Directly counted bacteria in a trout farm and its effluent. Aquacult. Fish. Manage. Vol 24, no. 1, pp. 19 -27. • Pharmaceuticals (? ) – Halling-Sorensen, B. et al. 1998. Occurrence, fate and effects of pharmaceutical substances in the environment—A review. Chemosphere. Vol 36, no. 2, pp. 357 -393. Jan. (Nice abstract. Unfortunately, article is in German. )
References • Claude E. Boyd. Guidelines for aquaculture effluent management at the farm-level. Aquaculture. Vol 226 Issues 14, Oct. 2003. pp 101 -112. • USEPA. BMPs for CAAP Facilities. www. epa. gov/guide/aquaculture.