Recently very popular Recirculating Aquaculture System ( RAS): How to operate it ?
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Note:
During my work in UK I have cultured prawn(M.rosenbergii) using RAS. I have also operated M. rosenbergii hatchery for several years using RAS.
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Recirculating aquaculture systems (RAS) are used in home aquaria, for fish and shrimp production where water exchange is limited or impossible due nonavailability of required salt or fresh water. Here same water has to repeatedly use through biofiltration to reduce ammonia toxicity. The main benefit of RAS is the ability to reduce the need for fresh, clean water while still maintaining a healthy environment for fish and shrimp. To operate RAS economically RAS must have high fish stocking densities.
Water treatment processes needed in a recirculating aquaculture system:
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A series of treatment processes is utilized to maintain water quality in intensive fish farming operations. These steps are often done in order or sometimes in tandem. After leaving the tanks holding fish/shrimp water is first treated for solids before entering a biofilter to convert ammonia to NO3.Then degassing and oxygenation is done often followed by heating/cooling and sterilization. Each of these processes can be completed by using a variety of different methods and equipment.
Biofiltration :
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All RAS relies on biofiltration to convert ammonia (NH4+ and NH3) excreted by the fish into nitrate. Ammonia is a waste product of fish metabolism and high concentrations (>.02 mg/L) are toxic to most finfish. Nitrifying bacteria are chemoautotrophs that convert ammonia into nitrite then nitrate. A biofilter provides a substrate for the bacterial community, which results in thick biofilm growing within the filter. Water is pumped through the filter, and ammonia is utilized by the bacteria for energy. Nitrate is less toxic than ammonia (>100 mg/L), and can be removed by a denitrifying biofilter or by water replacement. Stable environmental conditions and regular maintenance are required to ensure the biofilter is operating efficiently.
Solids removal:
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In addition to treating the liquid waste excreted by fishes solid waste must also be treated. This is done by concentrating and flushing the solids out of the system. The simplest method for removing solids is the creation of settling basin where the relative velocity of the water is slow and particles can settle at the bottom of the tank. then these are either flushed out or vacuumed out manually using a siphon. Typical RAS solids removal involves a sand filter or particle filter where solids become lodged and can be periodically backflushed out of the filter. Another common method is the use of a mechanical drum filter where water is run over a rotating drum screen that is periodically cleaned by pressurized spray nozzles. In order to remove extremely fine particles or colloidal solids a protein fractionator may be used with or without the addition of ozone (O3).
Oxygenation:
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Reoxygenating the system water is a crucial part to obtaining high production densities. . Dissolved oxygen levels can be increased through aeration or oxygenation.
pH control :
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In all RAS pH must be carefully monitored and controlled. The first step of nitrification in the biofilter consumes alkalinity and lowers the pH of the system. Keeping the pH in a suitable range (6.0-9.0) is crucial to maintain the health of both the fish and biofilter. pH is typically controlled by the addition of alkalinity in the form of lime (CaCO3) or sodium hydroxide (NaOH).
Temperature control:
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All fish species have a preferred temperature range. Temperature is controlled through the use of submerged heaters, heat pumps, chillers, and heat exchangers.
Biosecurity:
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Disease outbreaks occur more readily when dealing with the high fish stocking densities typically employed in intensive RAS. Outbreaks can be reduced by operating multiple independent systems with the same building and isolating water to water contact between systems by cleaning equipment and personnel that move between systems. The use of a Ultra Violet (UV) or ozone water treatment system also reduces the number of free floating virus and bacteria in the system water.
Writer M kabir Ahamed Sir
-----------------------------
Note:
During my work in UK I have cultured prawn(M.rosenbergii) using RAS. I have also operated M. rosenbergii hatchery for several years using RAS.
--------------------------------------------------------------------
Recirculating aquaculture systems (RAS) are used in home aquaria, for fish and shrimp production where water exchange is limited or impossible due nonavailability of required salt or fresh water. Here same water has to repeatedly use through biofiltration to reduce ammonia toxicity. The main benefit of RAS is the ability to reduce the need for fresh, clean water while still maintaining a healthy environment for fish and shrimp. To operate RAS economically RAS must have high fish stocking densities.
Water treatment processes needed in a recirculating aquaculture system:
-----
A series of treatment processes is utilized to maintain water quality in intensive fish farming operations. These steps are often done in order or sometimes in tandem. After leaving the tanks holding fish/shrimp water is first treated for solids before entering a biofilter to convert ammonia to NO3.Then degassing and oxygenation is done often followed by heating/cooling and sterilization. Each of these processes can be completed by using a variety of different methods and equipment.
Biofiltration :
------
All RAS relies on biofiltration to convert ammonia (NH4+ and NH3) excreted by the fish into nitrate. Ammonia is a waste product of fish metabolism and high concentrations (>.02 mg/L) are toxic to most finfish. Nitrifying bacteria are chemoautotrophs that convert ammonia into nitrite then nitrate. A biofilter provides a substrate for the bacterial community, which results in thick biofilm growing within the filter. Water is pumped through the filter, and ammonia is utilized by the bacteria for energy. Nitrate is less toxic than ammonia (>100 mg/L), and can be removed by a denitrifying biofilter or by water replacement. Stable environmental conditions and regular maintenance are required to ensure the biofilter is operating efficiently.
Solids removal:
---------
In addition to treating the liquid waste excreted by fishes solid waste must also be treated. This is done by concentrating and flushing the solids out of the system. The simplest method for removing solids is the creation of settling basin where the relative velocity of the water is slow and particles can settle at the bottom of the tank. then these are either flushed out or vacuumed out manually using a siphon. Typical RAS solids removal involves a sand filter or particle filter where solids become lodged and can be periodically backflushed out of the filter. Another common method is the use of a mechanical drum filter where water is run over a rotating drum screen that is periodically cleaned by pressurized spray nozzles. In order to remove extremely fine particles or colloidal solids a protein fractionator may be used with or without the addition of ozone (O3).
Oxygenation:
---------
Reoxygenating the system water is a crucial part to obtaining high production densities. . Dissolved oxygen levels can be increased through aeration or oxygenation.
pH control :
-------
In all RAS pH must be carefully monitored and controlled. The first step of nitrification in the biofilter consumes alkalinity and lowers the pH of the system. Keeping the pH in a suitable range (6.0-9.0) is crucial to maintain the health of both the fish and biofilter. pH is typically controlled by the addition of alkalinity in the form of lime (CaCO3) or sodium hydroxide (NaOH).
Temperature control:
--------
All fish species have a preferred temperature range. Temperature is controlled through the use of submerged heaters, heat pumps, chillers, and heat exchangers.
Biosecurity:
---------
Disease outbreaks occur more readily when dealing with the high fish stocking densities typically employed in intensive RAS. Outbreaks can be reduced by operating multiple independent systems with the same building and isolating water to water contact between systems by cleaning equipment and personnel that move between systems. The use of a Ultra Violet (UV) or ozone water treatment system also reduces the number of free floating virus and bacteria in the system water.
Writer M kabir Ahamed Sir
: How to operate it ?){kind=link}
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