Recirculation cultivation systems ( RAS ) are used in home aquariums and for fish production where limited water exchange and biofiltration use are needed to reduce toxicity of ammonia. Other types of filtering and environmental controls are often also needed to maintain clean water and provide suitable habitats for fish. The main benefit of RAS is the ability to reduce the need for clean and fresh water while maintaining a healthy environment for fish. To operate economically, commercial RAS must have high fish density, and many researchers are currently conducting research to determine whether RAS is an intensive, intensive cultivation form.
Video Recirculating aquaculture system
Proses pengolahan air RAS
A series of treatment processes are used to maintain water quality in intensive fish cultivation operations. These steps are often performed sequentially or sometimes simultaneously. After leaving the mother ship the water fish is first treated for solids before entering the biofilter to convert ammonia, subsequent degassing and oxygenation occurs, often followed by heating/cooling and sterilization. Each of these processes can be solved using a variety of different methods and tools, but not all should be done to ensure a healthy environment that maximizes the growth and health of the fish.
Biofiltration
All RASs depend on biofiltration to alter the ammonia (NH 4 and NH 3 ) excreted by the fish to nitrate. Ammonia is a fish waste product of metabolism and high concentrations (& gt;.02, mg/L) are toxic to most fish. Nitrifying bacteria are chemoautotrophs that convert ammonia to nitrites and nitrates. Biofilter provides a substrate for the bacterial community, which produces thick biofilms that grow inside the filter. Water is pumped through filters, and ammonia is used by bacteria for energy. Nitrate is less toxic than ammonia (100 mg/L), and can be removed by denitrification biofilter or by water replacement. Stable environmental conditions and routine maintenance are needed to ensure the biofilter operates efficiently.
Solid Removal
In addition to treating liquid waste disposed of by fish, solid waste must also be treated, this is done by concentrating and watering solids from the system. Eliminating solids reduces bacterial growth, oxygen demand, and disease proliferation. The simplest method to remove solids is the creation of deposition basins where the relative speed of slow water and particles can settle at the bottom of the tank where they are removed or emptied manually using siphon. However, this method is not feasible for RAS operations where small traces are desirable. The typical removal of RAS solids involves sand filters or particle filters in which solids become stuck and can be periodically rinsed from the filter. Another common method is the use of a mechanical drum filter in which water flows over a rotating drum screen that is periodically cleaned with a pressurized spray nozzle, and the resulting slurry is treated or sent to the drain. To remove very fine particles or colloidal solids, protein fractionators can be used with or without ozone addition (O 3 ).
Oxygenation
System water reoxygenation is an important part of achieving high production density. Fish need oxygen to metabolize food and grow, just like the bacterial community in biofilter. The level of dissolved oxygen can be increased through two methods of aeration and oxygenation. In air aeration is pumped through aerial stones or similar devices that create small bubbles in the water column, this results in a high surface area where oxygen can dissolve into water. In general, due to the slow gas dissolution rate and the high air pressure required to make small bubbles, this method is considered inefficient and the water is even oxygenated by pumping pure oxygen. Various methods are used to ensure that during oxygenation all the oxygen dissolves into the water column. Careful calculations and considerations should be given to the oxygen requirements of the given system, and that demand should be met with oxygenation or aeration equipment.
pH control
In all RAS pH should be carefully monitored and controlled. The first step of nitrification in biofilter consumes alkalinity and lowers the pH of the system. Keeping pH within the appropriate range (5.0-9.0 for freshwater systems) is very important to maintain the health of fish and biofilter. The pH is usually controlled by the addition of alkalinity in the form of lime (CaCO 3 ) or sodium hydroxide (NaOH). Low pH will cause high levels of dissolved carbon dioxide (CO 2 ), which may prove toxic to fish. pH can also be controlled by degassing CO 2 in packed columns or with aerators, this is necessary in intensive systems especially where non-aerated oxygenation is used in the tank to maintain O 2 levels.
Temperature control
All fish species have preferred temperatures above and below which fish will experience negative health effects and eventually death. Warm water species like Tilapia and Barramundi prefer water 24 Â ° C or warmer, while cold water species such as trout and salmon prefer water temperatures below 16 Â ° C. Temperature also plays an important role in dissolved oxygen concentration (DO) , with higher water temperatures having lower values ​​for DO saturation. Temperatures are controlled through the use of submerged heaters, heat pumps, coolers, and heat exchangers. All four can be used to keep the system operating at optimal temperatures to maximize fish production.
Biosecurity
Outbreaks of disease are more likely to occur when confronted with the high fish stocking densities typically used in intensive RAS. Epidemics can be reduced by operating several independent systems with the same building and isolating water into water contact between systems by cleaning equipment and personnel moving between systems. Also the use of Ultra Violet (UV) or ozone water treatment systems reduces the number of free-floating viruses and bacteria in the water system. This treatment system reduces the loading of diseases occurring in distressed fish and thus reduces the possibility of outbreaks.
Maps Recirculating aquaculture system
Benefits
- Reduce water requirements compared to raceway cultivation systems or ponds.
- Land requirements are reduced due to high stocking density
- Flexibility of site selection and independence of a large water source.
- Reduce the volume of liquid waste.
- Improve biosecurity and ease in treating disease outbreaks.
- Ability to monitor and control environmental conditions to maximize production efficiency. Similarly, independence from weather and variable environmental conditions.
Loss
- High initial investment in materials and infrastructure.
- High operating costs are mostly due to electricity, and system maintenance.
- The need for highly trained staff to monitor and operate the system.
Custom type RAS
Aquaponics
Combining plants and fish in RAS is called an aquaponic. In this type of ammonia system produced by fish is not only converted to nitrate but also disposed of by plants from water. In an aquaponic system, fish effectively fertilize plants, this creates a closed loop system in which very little waste is generated and inputs are minimized. Aquaponik provides benefits for being able to harvest and sell many plants.
Aquarium
Commercial aquariums and commercial aquariums inland are forms of RAS where water quality is controlled with extreme caution and dense stocking of fish is relatively low. In this system the goal is to display fish rather than produce food. However, biofilter and other forms of water treatment are still used to reduce the need to exchange water and maintain water clarity. Just as in traditional RAS water should be removed periodically to prevent nitrates and other toxic chemicals from building inside the system. Beach aquariums often have high water exchange rates and are usually not operated as RAS because of their proximity to large bodies of clean water.
References
External links
- Circulating the Design Design of a Aquaculture System
- Circulating Aquaculture Considerations, Design, and Management
- Water Reuse System Engineering Design
Source of the article : Wikipedia
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