Fish in the Loop: Exploring RAS - Julie Hansen Bergstedt
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Fish in the Loop: Exploring RAS Julie Hansen Bergstedt, DTU Aqua, Denmark
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Fish in the Loop: Exploring RAS - Julie Hansen Bergstedt
- 1. Fish in the loop: Exploring RAS Julie Hansen Bergstedt & Carlos Octavio Letelier-Gordo Section for Aquaculture Technical University of Denmark DTU Aqua National Institute of Aquatic Resources
- 2. Challenges of the 21st century 2 Challenges: o Climate change o Population growth o Biodiversity o Water availability Actions Reduce: o Emissions o Water utilization o Land use
- 3. Global water availability 3 40% gap in water supply compared to demand in 2030 3% is freshwater, of which 1 % is easily accessible * 400 l in RAS
- 4. Aquaculture Consumption Ornamental Conservation 4 425 species of animals, plants, and algae cultivated worldwide 22 species account for >75% of global production
- 5. Global aquaculture production 5 The largest volume (89%) of fish is produced in Asia SHARE OF AQUACULTURE IN TOTAL FISHERIES AND AQUACULTURE PRODUCTION BY MAJOR SPECIES GROUP, 2020 WORLD AQUACULTURE PRODUCTION, 19912020
- 6. Production systems Cages and pens Open flow Recirculating systems 6 Land-based
- 7. Resource utilization 7 The degree of recirculating is based on make up- water (MUW) pr. kg feed Less CO2 emission, and water and land used System m3/kg feed Flow through >50 Re-use RAS 1-50 Conventional RAS 0.1-1 Next gen RAS <0.1 Martins et al. 2010 Increased energy consumption due to additional components
- 8. Selection of species 8 Seawater Cubes RAS Unit, 120 m2, 8 tonnes of fish Danish salmon, RAS in construction, 7500 m2, 1200 tonnes of fish Matching production cost with demand Assessing the market and project profitability Geographical location: - Availability of electricity, water supply and work force - Ecology of selected species (cooling systems are expensive)
- 9. 9 Requirement of the fish Water flow Temperature Salinity pH Light conditions Dissolved gasses Stocking density Feed composition Feeding rate Noise Tank design Chemical stressors Physical/perceived stressors Overall animal health Growth Disease resistance Reproduction Ineffective utilization of nutrients Environment Feed Water quality
- 10. Recirculating aquaculture system 10 Gas control (O2 and CO2) Ammonia (NH3) Removal of solids Control of pathogens End-of-pipe- treatment Feed and O2 Solids and metabolic byproducts /Ozone
- 11. Feed 11 Standard growth rate (SGR) Feed conversion ratio (FCR) Digestibility The majority of the cost is due to feed (46%) Feed input Biomass produced 1 kg feed 0.9 kg 0.45 kg 0.34 kg 0.24 kg Feed Egestion (faeces) Ingestion Growth= Assimilation-Respiration Assimilation Excretion (NH3) Respiration A large fraction of the animal can be eaten ( 60%)
- 12. Metabolism of fish Metabolic rate Energy expenditure during a specific period Oxygen consumption (MO2): Standard metabolic rate (SMR) Maximum metabolic rate (MMR/ MO2max) Aerobic scope (AS) 12 0 50 100 150 200 250 300 350 400 450 0 2 4 6 8 10 12 14 16 18 20 22 24 MO 2 (mg O 2 kg -1 h -1 ) Time (h) MMR SMR AS Increase in O2 demand after feeding while the fish are digesting + during increased activity levels Automatization of oxygen supply !
- 13. Controlling gasses Oxygen and carbon dioxide consumed and produced by fish and microbes (biofilter) Dissolved oxygen (DO) conc: 80-100% - Aeration (90-100% of air sat) - Pure oxygen for supersaturation 0.5 kg O2 pr kg feed CO2: >15 mg/L 1.4 g pr g O2 consumed 13 200-300% saturation Unfed Tench/doctor fish (Tinca tinca) O2 added CO2 removed O2 consumption
- 14. 14 Toxic ammonia absent at pH < 7 TAN produced 35g/kg feed TAN = total ammonia nitrogen = NH4-N + NH3-N Ammonia and biofilters Langenfeld et al. 2021 Nitrifying bacteria pH Addition of bicarbonate to maintain alkalinity and buffering capacity of the system pH of 6.5-8 NH3: >0.2 mg/L NO2: >0.5 mg/L NO3: >300 mg/L Summerfelt et al. 2015
- 15. Tank design: Meet species demand (pelagic of bottom dwelling) Circular, square, and octagonal utilization of space and strength of design Particle residence time Self-cleaning effect 15 Solids removal and tank design Egestion + feed waste Excretion (NH3) Respiration Feed Solids Protein, fat, carbohydrate Mechanical filtration Volume, numbers, life- stages to accommodate? 1 kg feed produces 8 L of waste (sludge) Total suspended solids (TSS) TSS= 0.25 * kg feed fed (DM)
- 16. 16 Control of pathogens UV Safe for the fish Turbidity of water affects efficiency supplement with proper filtration Ozone Efficient oxidation of organic matter Flocculation properties of suspended solids Hazardous to fish and people Chemical NaCl, H2O2, formalin, chlorine based compounds, NaOH, iodine solutions, No use of antibiotics Inlet water Staff Eggs Between batches Outbreaks Disease in one part of the system will spread to others ! Dose vs effect Treating the fish without harming the biofilter
- 17. Components of RAS 17 Control of pathogens Gas control (O2 and CO2) Removal of metabolic by products (NH3) Removal of solids Ozone + Control of environment (temp, gasses) Reduced use of water No escapes/effect on wild populations Waste treatment - High investment cost Technological knowledge Complex system Flow is key! End-of-pipe- treatment In Out
- 18. 18 Thank you Julie Hansen Bergstedt juhala@aqua.dtu.dk