WATER RECIRCULATING SYSTEM IN FISH FARMING

In a recirculting or flowthrough system of fish farming, the cultured fish grows more faster and bigger. A recirculating aquaculture system is an enclosed system where the only water replacement is thewater lost to evaporation and cleaning. These systems are being deployed in developed countries such as the United States wher coastal land costs and labor costs are very high. The majority of tilapia grown in the US is from
these types of systems. There are several advantages in
using recirculating aquaculture
systems over traditional fish
farming systems: lower water requirements - a properly designed and operating RAS replaces lessthan 5% of the total water volume on a daily basis. lower land requirements - in locations where land costs
are very high, some sort of
RAS should always be
considered since they can
produce a large volume of
aquacultured product from a relatively small area. The
amount of land required is
less than 1/20th of the
amount required for
traditional pond farming. reduced labor requirements - a typical 100 metric ton per year RAS can
be run by as few as two
people, which is at least a
fivefold reduction in labor
usage versus traditional fish
farming methods. increased control over water quality parameters - having control over water temperature allows a RAS
producer to grow species
which could not normally be
raised in a given geographic
area. This can provide a key market advantage. The
traditional fish farmer
essentially has no control
over water temperature and
must grow a species suited to
the local environment or be a seasonal grower. Other
important water quality
parameters such as dissolved
oxygen can theoretically be
maintained at optimum
levels in RAS, which leads to higher growth rates. lower risk of negative impact from adverse
weather conditions - the risk of crop loss from a natural disaster can be eliminated in a properly sited and constructed RAS. The
traditional fish farmer is
more vulnerable to natural disasters and the effects of
natural weather patterns. By
rearing fish indoors, the RAS
producer is not limited by
inclimate weather. An early
season cold spell can spell disaster for a traditional fish
farmer who has waited a
week too long to harvest. lower risk of creating adverse environmental impacts - if left untreated, the discharge plume from traditional fish and shrimp
farms is essentially a source
of pollution of local water
bodies. Recirculating systems
treat and reuse the water and there is zero discharge
to the local environment.
RAS should be selected when
an environmentally friendly
solution to the growing
demand for seafood is required. increased biosecurity - a properly designed and managed RAS has complete control over biosecurity
concerns, whereas a traditional open system is open to attack. RAS Design RAS are typically run as intensive or super-intensive systems to compensate for the relatively high construction and operational costs.
Their design and operation are
varied. Circular tanks or raceways are the most common forms of
tank design. Round tanks funnel
wastes effectively, while raceways
are excellent for manipulation of
the stock and harvesting. Stocking
densities as high as 0.75 pounds per gallon have been deployed in
recirculating tilapia systems. Super-intensive and intensive RAS
have a high input demand for
quality aquaculture feeds. The
large inputs of feeds into the
system are of major concern in the design phase of a RAS. All RAS must utilize processes to remove solid wastes, oxidize ammonia and nitrite-nitrogen and oxygenate the water. Feeding rate, feed composition, fish metabolic rate and quantity of wasted feed can all have a major detrimental impact
on tank water quality and must be accounted for in the design and anagement of a RAS. Aquaculture feeds mainly consist of protein, carbohydrates, fat, ash and water. The portion of feed not utilized by the fish is excreted as an organic waste (fecal solids). These fecal solids, along with uneaten feed, are broken down by bacteria in the system. This process consumes oxygen and generates ammonia-
nitrogen and must be dealt with in design and operation. To minimize their impact on water quality, waste solids need to be removed from the system as quickly as possible. Waste solids can be classified into four categories: settleable suspended floating dissolved Settleable solids should be removed from the water in the tank as rapidly as possible. Settleable solids are those that will settle out of water within one hour under still conditions. Settleable solids can either be allowed to settle within round culture tanks, where they move towards the center drain, or they can be kept in suspension and then removed. Suspended solids are those that
will not settle out of the water
column under still conditions
within one hour. Fine suspended
solids smaller than 30 microns can
contribute more than 50% of the total suspended solids load in a
RAS. Dissolved organic solids
(proteins) can also contribute
significantly to the total oxygen
demand of RAS if left untreated.
Dissolved solids and fine suspended solids can be removed using a process called foam fractionation or protein skimming. Foam fractionation introduces air bubbles at the bottom of a closed column. As the bubbles rise through the water column, fine suspended solid particles attach to
the bubbles surface, creating a
protein-rich foam at the top of the column. The foam buildup is then channeled out of the fractionation unit to a waste collection tank. A properly designed foam fractionation unit can reduce water turbidity and oxygen demand in the culture tank. Another option is to use bioenergetics to advantage in managed bacterial floc systems
deploying active manipulation of
the C:N ratio and the aerobic and
anaerobic states of the RAS. Perhaps the most important water quality variable in RAS is unionized ammonia nitrogen (NH3). To maintain a safe concentration of NH3 in the culture environment the
rate of removal must equal the rate of production at the maximum sustainable capacity of the system.The efficiency with which the treatment system removes ammonia from the system, the ammonia production rate, and the desired concentration of ammonia
nitrogen within the tank will
determine the recirculating flow
rate. While there are a number of
different technologies available for removing ammonia-nitrogen from the water. CALL ON US FOR YOUR FLOW THROUGH POND CONSTRUCTION CALL 08032861326 FOR BETTER SERVICES

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