Transcript Slide 1

Function and Maintenance of Recirculating Aquaculture System (RAS) Components
Daniel Miller, Research Associate - Davis College of Agriculture Forestry and Consumer Sciences - West Virginia University
Introduction
Small scale recirculating aquaculture systems (RAS) have been employed in
many educational programs. This poster is designed to provide basic
information on the set-up, operation and maintenance of the components
that keep the water quality suitable for the fish in the system.
All fish consume oxygen and feed. The consumption of oxygen and feed
result in the production of carbon dioxide, ammonia, and solid waste. Each
of the components in a recirculating system are helping to keep the level of
these chemicals in a balance that will allow the fish to grow in a low stress
environment. Intensive recirculating aquaculture systems typically can
sustain up to 0.5 pounds of fish per gallon. Maintaining the proper water
level (make-up water) is critical for all components.
The Biofilter = The Kidney
A healthy brain remains connected to and helps control all of the organs in
the body. Good management practices will include routine checks of all
the components in a recirculating aquaculture system on a regular
basis. Good record keeping is essential to good management. With
higher feeding rates the management level must increase. Adding feed
to the system will drive the following reactions:
1) Increase oxygen use in the system (1 lb. feed will use +/- 0.5 lb. oxygen)
One of the most common problems with recirculating systems is the
inability of the biofilter to convert ammonia fast enough to keep the water
non-toxic for the fish. This can be managed from the start by filling the
system with water, adding about 5 mg/l of ammonia (high nitrogen
fertilizer) and monitoring the rate that the ammonia level drops.
Proper development of the bacteria in the biofilter is critical to the health
of the fish when stocked into the system. Typically it will take 8 to 10
weeks for a biofilter to be conditioned enough for stocking fish. To
reduce risk of failure, stock a well conditioned system with 1-2 grams of
fish per gallon of system water and check NH3 and NO2 daily. Remember
that the protein in the fish feed is what controls the production of toxic
ammonia in the system. So it is wise not to increase the feed inputs too
rapidly. Monitoring the ammonia and nitrite levels is good management.
Typically 100 lbs. of feed will produce 3 lbs. of ammonia. Two types of low
maintenance biofilters are seen in photos below.
Critical Components
Management = The Brain
Much like the kidney cleans toxins from the blood, in a recirculating
aquaculture system the biofilter converts toxic ammonia (excreted by the
fish gills) into non-toxic nitrate, in a two step process that uses natural
(nitrifying) bacteria. The biofilter is a chamber that cultivates nitrifying
bacteria by providing a large surface area where the bacteria will attach.
By converting ammonia into nitrate the biofilter uses oxygen and
alkalinity. Solid waste should be minimized in the water or it will
encourage non-nitrifying bacteria (undesirable) to develop and compete
with the nitrifying (good) bacteria.
Fluidized bed sand filter
Moving bed bioreactor
2) Increase solid waste generation (1 lb. feed → +/- 0.3 lb. solid waste)
3) Increase carbon dioxide production
4) Decrease system pH
5) Decrease alkalinity (1 lb. feed will use +/- 0.3 lb. of alkalinity)
On-line references are available from the aquanic.org web site. Specific
information on RAS components can be found at:
http://srac.tamu.edu/index.cfm?catid=24
A wide variety of general fact sheets are found at: http://srac.tamu.edu/
Solid settling tank with airlifts
Aeration = The Lungs
Hydroponics / Aquaponics
Just like lungs, aeration will increase the oxygen levels in the water as well
as remove the carbon dioxide produced from respiration. Aeration can be
used to return the water to the circular tanks (using an airlift) and create a
circular flow that draws solids to the center of the tank just like tea leaves
go to the center of a tea cup when stirred with a spoon. What causes this
to happen?
Raising plants without the use of soil is called hydroponics. Plants can be
introduced into any recirculating aquaculture system to utilize the
dissolved nutrients that build up in the water. Phosphorus (P) and
nitrogen (N) are typically discarded from fish farms in the effluent. P and
N are used by the plants for growth. The combination of growing fish and
plants in the same water is called aquaponics.
The two airlifts seen at the front of the solid settling tank in the above
photo are moving water and solid waste from the center of two production
tanks (not seen) into the settling area where solids are removed. Intensive
production systems need to design for rapid concentration and removal of
the solids in order to maintain good water quality.
Selecting the proper plants to grow will depend on water temperature and
local markets. Keeping available nutrients in balance can be a challenge
in aquaponics.
When aeration is used in multiple areas to move or aerate water (red
valves on left of above photo) it is important to check all outlets after
adjusting the air flow in one area. By increasing the flow in one area a
reduction of flow in another area can result in problems.
Water Chemistry and Record Keeping
The Pump = The Heart
The pump is the heart of the operation. Air pumps are used to circulate
and lift water (air lift) up to 10 inches by introducing air at the bottom of a
narrow pipe. Air lifts are common in educational and small commercial
tank systems because they use much less electricity than water pumps so
they can reduce the cost of production. An additional advantage is that air
pumps also remove unwanted carbon dioxide and add needed oxygen.
Water pumps are used to circulate and lift water as high as needed. They
will break-up solid waste which allows nutrients to be leached into the
water (not good) . Smaller waste particles are more difficult to settle and
remove from the system, which is important to good water quality. It is best
to place the pump above the water level to avoid siphon water damage. A
one-way valve on the outflow line will reduce back flow to the pump.
A well managed system will have a well maintained record book that
indicates the date that actions were taken, whether it is the amount of feed
fed or water analysis results using the test kit. During the first months of
operation, and after any addition of fish to the system, ammonia and nitrite
tests should be done regularly.
Alkalinity is a buffer for keeping the pH in a pond from going too high on a
sunny afternoon, or too low before sunrise. The level of alkalinity in the
water should be maintained between 100 and 300 mg/l. A bicarbonate
(calcium or sodium) should be added to the system water whenever the
alkalinity drops below 100 mg/l. How often that is needed will depend on the
feeding rate.
If ammonia is causing problems (>2 mg/l depending on the pH) the quickest
fix is to flush with clean water and stop feeding until levels are reduced.
High levels of nitrite often follow ammonia spikes and can cause problems
by interfering with oxygen uptake at the gills. This usually results in a
brownish coloration of gill tissue. Salt can be added (1 lb. NaCl / 50 gallons)
to reduce the toxic effect of nitrites in an unbalanced system. Ammonia
production can be reduced with rapid (5-10 min.) removal of solid waste.
Biosecurity = The Skin
The largest organ of the body, skin provides a layer of protection against
many diseases. A biosecurity plan should be a written updatable
document that describes the actions taken to avoid disease as well as the
actions taken to minimize the spread of disease. The biosecurity plan
becomes valuable when it is implemented by training all of the workers
about these actions. This includes ways to reduce stress in fish culture
and handling. Careful observation of changes in fish behavior is one
small part of monitoring potential diseases.
References for aquatic diseases can be found on the web at:
http://srac.tamu.edu/index.cfm?catid=26
Harvest of healthy fish – note the normal color of gills