A Commercial-Scale Aquaponic System Developed at the
University of the Virgin Islands
James E. Rakocy*, Donald S Bailey, R. Charlie Shultz, and
Jason J. Danaher
Agricultural Experiment Station
University of the Virgin Islands
RR 1, Box
10,000U.S.
Abstract
Aquaponics is the combined culture of fish and plants in
recirculating systems. Nutrients
generated by the fish, either by direct excretion or microbial breakdown of
organic wastes, are absorbed by plants cultured hydroponically. Fish provide most of the nutrients required
for plant nutrition. As the aquaculture effluent flows through the hydroponic
component of the recirculating system, fish waste metabolites are removed by
nitrification and direct uptake by plants, thereby treating the water, which
flows back to the fish rearing component for reuse.
The University of the Virgin Islands Aquaculture Program has
developed a commercial-scale aquaponic system.
The system consists of four fish rearing tanks (7.8 m3 each,
water volume), two cylindro-conical clarifiers (3.8 m3 each), four
filter tanks (0.7 m3 each), one degassing tank (0.7 m3),
six hydroponic tanks (11.3 m3 each, 214 m2 of plant
growing area), one sump (0.6 m3), and one base addition tank (0.2 m3). The system contains 110 m3 of
water and occupies a land area of 0.05 ha.
Major inputs are fish feed, water (1.5% of system volume daily on
average), electricity (2.21 kW), base [Ca(OH)2 and KOH] and
supplemental nutrients (Ca, K, Fe). The
system can produce nearly 5 mt of tilapia along with 1400 cases (24-30 heads
per case) of leaf lettuce or 5 mt of basil or a variety of other crops.
The UVI system represents an appropriate or intermediate
technology that can be applied outdoors under suitable growing conditions or in
an environmentally controlled greenhouse.
The system conserves and reuses water, recycles nutrients and requires
very little land. The system can be used
on a subsistence level or commercial scale.
Production is continuous and sustainable. The system is simple, reliable and robust.
The UVI aquaponic system does require a relatively high capital investment,
moderate energy inputs and skilled management, though management is easy if
production guidelines are followed.
Introduction
Aquaponics is the combined culture of fish and plants in
recirculating systems. Nutrients, which
are excreted directly by the fish or generated by the microbial breakdown of
organic wastes, are absorbed by plants cultured hydroponically (without
soil). Fish feed provides most of the
nutrients required for plant growth. As
the aquaculture effluent flows through the hydroponic component of the
recirculating system, fish waste metabolites are removed by nitrification and
direct uptake by the plants, thereby treating the water, which flows back to
the fish-rearing component for reuse.
Aquaponics has several advantages over other recirculating
aquaculture systems and hydroponic systems that use inorganic nutrient
solutions. The hydroponic component
serves as a biofilter, and therefore a separate biofilter is not needed as in
other recirculating systems. Aquaponic
systems have the only biofilter that generates income, which is obtained from
the sale of hydroponic produce such as vegetables, herbs and flowers. In the UVI system, which employs raft
hydroponics, only calcium, potassium and iron are supplemented. The nutrients provided by the fish would
normally be discharged and could contribute to pollution. Removal of nutrients by plants prolongs water
use and minimizes discharge. Aquaponic
systems require less water quality monitoring than individual recirculating
systems for fish or hydroponic plant production. Aquaponics increases profit potential due to
free nutrients for plants, lower water requirements, elimination of a separate
biofilter, less water quality monitoring and shared costs for operation and
infrastructure.
Design Evolution and
Operation
Aquaponic research at UVI began with six replicated systems
that consisted of a rearing tank (12.8 m3), a cylindro-conical
clarifier (1.9 m3), two hydroponic tanks (13.8 m2) and a
sump (1.4 m3) (Rakocy 1997).
The hydroponic tanks (6.1 m long by 1.22 m wide by 28 cm deep) were
initially filled with gravel supported by wire mesh above a false bottom (7.6
cm). The gravel bed, which served as a
biofilter, was alternately flooded with culture water and drained. Due to the
difficulty of working with gravel, the gravel was removed and a raft system,
consisting of floating sheets (2.44 m long x 1.22 m wide x 3.8 cm thick) of
polystyrene, was installed. A rotating
biological contactor (RBC) was then used for nitrification. Effluent from the clarifier was split into
two flows, one going to the hydroponic tanks and the other to the RBC. These flows merged in the sump, from which
the treated water was pumped back to the rearing tank.
The rearing tank in this design proved to be too large
relative to the plant growing surface area of the hydroponic tanks, or,
conversely, the hydroponic tanks were too small relative to the size of the
rearing tank. When the rearing tank was
stocked with Nile tilapia (Oreochromis
niloticus) at commercial rates, nutrients rapidly accumulated to levels
that exceeded the recommended upper limits for hydroponic nutrient solutions
[2,000 mg/L as total dissolved solids (TDS)] (Rakocy et al. 1993). Using Bibb lettuce, the optimum ratio between
the fish feeding rate and plant growing area was determined (Rakocy 1989). At this ratio (57 g of feed/m2 of
plant growing area/day) the nutrient accumulation rate decreased and the
hydroponic tanks were capable of providing sufficient nitrification. Therefore, the RBCs were removed and the fish
stocking rates were reduced to levels that allowed feed to be administered near
the optimum rate for good plant growth.
The experimental system has been scaled up three times. In the first scale-up, the length of each
hydroponic tank was increased from 6.1 m to 29.6 m. The optimum design ratio was used to allow
the rearing tank to be stocked with tilapia at commercial levels (for a
diffused aeration system) without excessive nutrient accumulation. In the second scale-up, the number of
hydroponic tanks (29.6 m in length) was increased to six; the number of fish rearing tanks was increased to four
(each with a water volume of 4.4 m3); the number of clarifiers was increased to two;
four filter tanks (0.7 m3 each) were added and the sump was reduced to 0.6 m3. This production unit, commercial aquaponics 1
(CA1), represented a realistic commercial scale, although there are many
possible size options and tank configurations.
The final scale-up, commercial aquaponics 2 (CA2), involved the
enlargement of the four fish rearing tanks (each with a water volume of 7.8 m3)
and the two clarifiers (each with a water volume of 3.8 m3) and the
addition of a 0.7-m3 degassing tank (Figure 1). The commercial-scale
units could be configured to occupy as little as 0.05 ha of land.
The rearing tanks and water treatment tanks were situated under
an opaque canopy, which inhibited algae growth, lowered water temperature,
which is beneficial for hydroponic plant production, and created more natural
lighting conditions for the fish.
The system used multiple fish rearing tanks to simplify
stock management. Tilapia production was
staggered in four rearing tanks so that one rearing tank was harvested every 6
weeks. The fish were not moved during
their 24-week growout cycle. In a
2.5-year production trial in CA 1 using sex-reversed Red tilapia, annual
production was 3,096 kg, based on the last 11 harvests out of 19 harvests
(Rakocy et al. 1997). Fingerlings,
stocked at 182 fish/m3, grew at an average rate of 2.85 g/day to a
size of 487 g. The final biomass
averaged 81.1 kg/m3. This was
equivalent to annual production of 175.7 kg/m3 of rearing tank
space. The average feed conversion and
survival were 1.76 and 91.6%
The stocking density appeared to be too high for maximum
growth and efficient feed conversion. Midway through each production cycle, ad libitum feeding leveled off at
approximately 5 kg per rearing tank. As
the fish grew in the last half of the production cycle, feed consumption did
not increase. Therefore more of the feed
was used for maintenance and less was used for growth, leading to a relatively
high feed conversion ratio for 487-g fish. In CA2 the stocking rate for red tilapia
has been lowered by 15% to 154 fish/ m3. The growth of Nile
tilapia was evaluated at a stocking rate of 77 fish/m3. With larger rearing tanks and higher growth
rates, it was anticipated that CA2 could produce 5 mt of tilapia annually.
Based on the results of 20 harvests (four for Red tilapia
and 16 for Nile tilapia) with the CA2 system,
Red tilapia grew to an average of 512.5 g (Rakocy et al. 2004a). The West Indian market prefers a colorful
whole fish that is served with its head on.
At this density production averaged 70.7 kg/m3, and the
growth rate averaged 2.69 g/day. Nile tilapia averaged 813.8 g, a preferable size for the
fillet market. At this density
production averaged 61.5 kg/m3, and the growth rate averaged 4.40
g/day. The stocking rates appeared to be
nearly optimal for the desired product size.
Nile tilapia attained a higher survival
rate (98.3%) and a lower feed conversion ratio (1.7) than Red tilapia (89.9%
and 1.8, respectively). Projected annual
production was 4.16 mt for Nile tilapia and
4.78 mt for Red tilapia.
Tank Dimensions
|
Pipe Sizes
|
Rearing tanks: Diameter: 3 m, Height: 1.2 m, Water volume:
7,800 L
Clarifiers: Diameter:
1.8, Height of cylinder: 1.2 m, Depth of cone: 1.1 m, Slope: 45º, Water
volume: 3,785 L
Filter and degassing tanks: Length: 1.8 m, Width: 0.76 m,
Depth: 0.61 m, Water volume: 700 L
Hydroponic tanks: Length: 30.5 m, Width: 1.2 m, Depth: 41
cm, Water volume: 11,356 L
Sump: Diameter: 1.2 m, Height: 0.9 m, Water volume: 606 L
Base addition tank:
Diameter: 0.6 m, Height: 0.9 m, Water volume: 189 L
Total system water volume: 111,196 L
Flow rate: 378 L/min, Pump: 0.37 kW Blowers: 1.1 kW (fish)
and 0.74 kW (plants)
Total land area: 0.05 ha.
|
Pump to rearing tanks: 7.6 cm
Rearing tanks to clarifier: 10 cm
Clarifiers to filter tanks: 10 cm
Between filter tanks: 15 cm
Filter tank to degassing tank: 10 cm
Degassing to hydroponic tanks: 15 cm
Between hydroponic tanks: 15 cm
Hydroponic tanks to sump: 15 cm
Sump to pump: 7.6 cm
Pipe to base addition tank: 1.9 cm
Base addition tank to sump: 3.2 cm
|
Figure 1. Current design of the UVI commercial aquaponic
system (CA2).
To achieve production of 5 mt, more research is needed on
types of feed (e.g., higher protein levels) and the delivery of the feed. To achieve an annual harvest of 5 mt for Nile tilapia, the average harvest weight must be 978 g,
an increase of 164 g over the current harvest weight. In addition to better feed and feed delivery,
it may be necessary to stock larger fingerlings or increase the stocking rate
slightly.
Production trials with the CA1 system employed two methods
of ad libitum feeding. A demand feeder, used initially, was replaced
by belt feeders, utilizing variable quantities of feed adjusted to meet the
demand. Neither method proved to be
entirely satisfactory. With demand
feeders, high winds would shake the feeder, which then dispensed too much feed,
or clumps of feed would block the funnel opening of the demand feeder, which
then delivered too little feed. The belt
feeders periodically failed, not delivering any of the daily feed ration. Both devices were expensive and required
support structures. In CA2 the fish were fed ad libitum by manual feeding three times daily, which proved to be
much more satisfactory.
In a CA1 production trial, DO levels were maintained at a
mean of 6.2 mg/L by high DO in the incoming water and by diffused aeration with
air delivered through 10 air stones (22.9 cm x 3.8 cm x 3.8 cm) around the
perimeter of the tank. In the last 12
weeks of the growout period, a 40-watt vertical lift pump was placed in the
center of the tank for additional aeration.
The pump pushed the floating feed to the perimeter of the tank and some
feed pellets were splashed out of the tank during initial feeding frenzies. Vigorous
aeration vented carbon dioxide gas into the atmosphere and prevented its
buildup. A high water exchange rate quickly removed suspended solids and toxic
waste metabolites (ammonia and nitrite) from the rearing tank. A 0.74-kW in-line pump moved water at an
average rate of 378 L/min from the sump to the rearing tanks (mean retention
time, 0.8 h). Values of
ammonia-nitrogen and nitrite-nitrogen in the rearing tanks averaged 1.47 and
0.52 mg/L, respectively. A pH of 7.2 was
maintained by frequently adding equal amounts of calcium hydroxide and
potassium hydroxide. Total alkalinity
averaged 56.5 mg/L as calcium carbonate.
In CA2 the vertical lift pump was eliminated, and the number
of air stones around the rearing tank perimeter was increased to 22 (15.2 cm x
3.8 cm x 3.8 cm). The air stones pushed
feed to the center of the tank and no feed was lost due to feeding frenzy
splashing. With larger water volumes, the retention time increased to an
average of 1.37 hours. A 1.1 kW blower provided sufficient aeration for the
fish rearing tanks while a 0.74 kW blower was used for the hydroponic tanks.
Effluent from the fish rearing tanks flowed into two 1.9-m3
clarifiers in the CA1 production trial.
Separate drains from two of the rearing tanks were connected to each
clarifier [see Rakocy (1997) for a detailed description]. The clarifiers removed settleable solids, but the amount of solids collected was
not as great with the 9.5-minute retention time in the production trial as it
had been in previous trials with longer retention times (>20 minutes). Therefore, in CA2 the clarifiers were
increased in size to 3.8 m3 and the retention time increased to 19
minutes. The bottom slope of the new
clarifiers was 45º as compared to 60º slopes in the 1.9-m3
clarifiers. Sludge was removed from the
clarifiers three times daily.
Settleable solids in the clarifiers adhered to the sides of
the cones and did not slide to the bottom where they could be removed by
opening the drain line. It was necessary to stock about 20 male tilapia in the
each clarifier. They were not fed. As these fish fed on organisms growing on
the clarifier walls, solids rolled to the cone bottom and were easily removed
by opening the drain line. The tilapia also swam into the rearing tank drain
lines and kept them free of biofouling organisms. Tilapia in the clarifiers
grew rapidly and needed to be replaced every 12 weeks with smaller (~ 50 g)
fingerlings. If they became too large, their swimming activity stirred up the
settled solids, which was counterproductive to clarification.
Suspended solids levels, which decline slightly on passage
through the clarifier, were reduced further before the effluent entered the
hydroponic tanks. Excessive solids were
detrimental to plant growth. Solids
adhered to plant roots, created anaerobic conditions and blocked nutrient
uptake. Two filter tanks in series, each
with a volume of 0.7 m3 and filled with orchard netting (1.9 cm
mesh), received effluent from the clarifier and removed considerable amounts of
suspended solids, which adhered to the orchard netting. In the CA1 production trial, total suspended
solids averaged 9.0 mg/L in the rearing tanks, 8.2 mg/L in the effluent from
the clarifiers (a 9% reduction) and 4.5 mg/L in the effluent from the filter
tanks (a 45% reduction). The filter
tanks were drained and the orchard netting was washed with a high-pressure
sprayer once or twice per week. Solids
from the filter tanks and clarifiers were discharged through drain lines into
two 16-m3, lined ponds, which were continuously aerated using air
stones. As one pond was being filled
over a 2 to 4-week period, water from the other pond was used to irrigate and
fertilize field crops.
A separate study showed that of the total amount of solids
removed from the system the clarifiers removed approximately 50% (primarily
settleable solids) while the filter tanks removed the remaining 50% (primarily
suspended solids).
The relatively slow removal of solids from the system (three
times daily from the clarifiers and 1-2 times weekly from the filter tanks) was
an important design feature. While
solids remained in the system, they were mineralized. The generation of dissolved inorganic
nutrients promoted vigorous plant growth.
In addition, filter-tank solids created anaerobic zones where
denitrification occurred. As water
flowed through the accumulated organic matter on the orchard netting, nitrate
ions were reduced to nitrogen gas.
Nitrate was the predominant nutrient in the aquaponic systems. High nitrate levels promoted vegetative
growth but inhibited fruiting. With
fruiting plants such as tomatoes, low nitrate concentrations maximized fruit production. Nitrate levels were controlled by regulating
the cleaning frequency of the filter tanks.
If the filter tanks were cleaned twice per week, there was less solids
accumulation, less denitrification and higher nitrate levels. If the filter tanks were cleaned once per
week, there was more solids accumulation, more denitrification and lower
nitrate levels.
Alkalinity is produced during denitrification and by plants which
excrete alkaline ions though their roots. There were periods when the pH did
not decline for weeks at a time, which was detrimental to plant growth since
calcium and potassium could not be supplemented through the addition of base.
To prevent periods of stable pH, the filter tanks were cleaned more frequently
(twice per week) and any accumulation of solids on the bottom of the hydroponic
tanks, which could be anaerobic, were removed.
Organic decomposition in the filter tanks produced carbon
dioxide, methane, hydrogen sulfide, nitrogen and other gases. If filter-tank effluent entered the hydroponic
tanks directly, it retarded the growth of plants near the inlet. Therefore, a 0.7-m3 degassing tank
was added to the CA2 system. Filter-tank
effluent entered the degassing tank and was vigorously aerated, venting
potentially harmful gasses into the atmosphere.
Degassing-tank effluent was split into three equal portions, each of
which passed through a set of two hydroponic tanks. In each set of tanks, water flowed 59.2 m
before returning to the sump and being pumped back to the fish rearing
tanks.
The hydroponic tanks retained the fish culture water for an
average of three hours before it returned to the fish rearing tanks. Each set of hydroponic tanks contained 48 air
stones (7.6 cm x 2.5 cm x 2.5 cm), located 1.22 m apart along the central axis
of the tank, which re-aerated and mixed the water, exposing it to a film of nitrifying
bacteria that grew on the tank surface areas, especially the underside of the
polystyrene sheets. In the CA1
production trial, DO increased from 4.0 to 6.9 mg/L on passage through the
hydroponic tanks (Rakocy et al. 1997).
Through direct nutrient uptake by plants or bacterial oxidation, Gloger
et al. (1995) found that the UVI raft hydroponic tanks removed an average of
0.56 g of total ammonia-nitrogen, 0.62 g of nitrite-nitrogen, 30.29 g of
chemical oxygen demand, 0.83 g of total nitrogen and 0.17 g of total
phosphorous per m2 of plant growing area per day using romaine
lettuce. The maximum sustainable wastewater
treatment capacity of raft hydroponics was found to be equivalent to a feeding
rate of 180 g/m2 of plant growing area/day. Therefore raft
hydroponics exhibited excess treatment capacity.
The optimum feeding rate ratio of 57 g of feed/m2
of plant growing area/day, needed to reduce nutrient accumulation, was
determined using the initial small-scale systems. Nutrient levels increased but
at a lower rate, and there was no filter tank. As the system design evolved to
the final commercial size (CA2), up to 5,600 L of water were dumped weekly (5%
of the system water volume) during the filter tank cleaning process, which
resulted in nutrient concentrations remaining in a steady state at feeding rate
ratios of 60 to 100 g/m2/day. This range of feeding rate ratios was
well within the wastewater treatment capacity of 180 g/m2/day. Therefore,
after an initial acclimation period of one month, it was not necessary to
monitor ammonia or nitrite values in the commercial-scale system provided that
the film on nitrifying bacteria on the underside of the rafts remained intact.
Several materials were used to construct the hydroponic
tanks. The best construction materials
consisted of poured concrete walls (40 cm high and 10 cm wide) and a 23-mil
high-density polyethylene tank liner.
The black liners used for CA1 absorbed considerable heat along the top
of the tank walls. For CA2 the portion
of the liners above the water level was painted white to reflect heat. Subsequently
UV-resistant, white liners were used.
The polystyrene sheets were painted white with a potable grade latex
paint to reflect heat and prevent the deterioration that results if it is
exposed to direct sunlight.
There were several advantages to raft culture. There was no
limitation on tank size. Rafts provided
maximum exposure of the roots to the culture water and avoided clogging. The sheets shielded the water from direct
sunlight and maintained lower than ambient water temperatures, which was
beneficial to plant growth. A disruption
in pumping did not affect the plant’s water supply. The sheets were easily moved along the
channel to a harvesting point, where they were lifted out of the water and
placed on supports at an elevation that was comfortable for workers.
A disadvantage of raft culture was that the plant roots were
vulnerable to damage caused by zooplankton, snails, leeches and other aquatic
organisms. Biological methods have been
successful in controlling these invasive organisms. Ornamental fish, particularly tetras (Gymnocorymbus ternetzi), were effective
in controlling zooplankton, and red ear sunfish (shellcrackers, Lepomis microlophus) were effective in
controlling snails. Shellcrackers also prey on leeches.
During the 2.5-year production trial for tilapia and lettuce
in CA1, total annual lettuce production averaged 1,404 cases (Rakocy et al
1997). Lettuce production cycles from
transplanting seedlings to harvest were 4 weeks. In 112 lettuce harvests,
marketable production averaged 27 cases per week and ranged from 13-38 cases
(24-30 heads/case). Average harvest
weight was 269 g for Sierra (red leaf), 327 g for Parris Island (romaine), 314
g for Jericho (romaine) and 265 g for Nevada (green
leaf). The plants were weighed after the
lower leaves were trimmed. Production
was always greater during the cooler winter months when water temperature
averaged 25.1ºC than in the summer months when water temperature averaged 27.5ºC.
Fish feed provided adequate levels of 10 of the 13 nutrients
required for plant growth. The nutrients
requiring supplementation were K, Ca and Fe.
During the production trial, 168.5 kg of KOH, 34.5 kg of CaO, 142.9 kg
of Ca(OH)2 and 62.7 kg of iron chelate (10%) were added to the
system, which was equivalent to the addition of 16.1, 3.3, 13.7 and 6.0 g,
respectively, for every kilogram of feed added to the system. The amount of Ca and K added was the result
of the quantity of base required to maintain pH at 7.2. The optimum pH value
for the UVI aquaponic system has been revised to 7.0. Rainwater was used in all the aquaponic
systems at UVI because the NaCl content of groundwater in the Virgin
Islands was too high.
Two species of pathogenic root fungi (Pythium myriotylum and P.
dissoticum) caused production to decline during the warmer months. Pythium
myriotylum caused root death while P.
dissoticum caused general retardation in the maturation rate of the
plant. CA2 was designed to lower water
temperature, through shading, reflective paint and heat dissipation manifolds
(attached to the blowers), in an effort to minimize the effects of Pythium.
A plant potting media containing coconut fibers (coir) was used to
produce transplants for CA2 instead of the peat-based potting media used for
CA1 because some peat products contain Pythium
spores. The use of resistant varieties
and antagonistic organisms also offer potential for Pythium control in aquaponic systems.
The only significant insect problem with lettuce was caused
by caterpillars of the fall armyworm and corn earworm. These caterpillars were controlled by twice
weekly sprays with Bacillus thuringiensis,
a bacterial pathogen that is specific to caterpillars.
Using the final design of system CA2 for production of basil
was evaluated (Rakocy et al. 2004b). Annual production was projected to be 5.0 mt
(Figure 2).
Figure 2. Basil production in the UVI aquaponic system (CA2).
Economics
The economics of the UVI aquaponic system is very site
specific. The cost of construction materials, labor and inputs such as feed,
chemicals and electricity vary widely from one country to another. In the Virgin Islands the current sales price for live tilapia is
US$6.60 per kg. Assuming that a commercial scale system can produce 5 mt of
tilapia annually, total annual income from fish sales will be $33,000.
The income from crop production depends on the production
level and commercial value of the crop. A number of crop production trials have
been conducted. Each crop requires a different planting density and length of production
cycle. The greatest annual income for the commercial-scale UVI system is
obtained by herbs such as chives and basil (Table 1). These production levels exceed
the market size on small islands. Intermediate income levels are obtained from
lettuce while fruiting crops such as cantaloupe and okra produce very low income
(Table 1).
It is recommended that a commercial operation consists of
six production units (systems). With a total of 24 fish rearing tanks, one fish
rearing tank can be harvested weekly, yielding 574 kg of fish. A consistent
amount of fish on a weekly basis facilitates market development. Based on
experience, this amount of tilapia can be sold weekly on a small island.
The best marketing strategy is direct sales to customers
either by delivering fish to restaurants and stores or by establishing a sales
outlet at the production site. With the latter strategy it is important to
select a location that is highly visible and convenient to customers. Selling
fish as a commodity will substantially reduce the sales price.
Table 1. Production parameters and income levels for
vegetables grown in the commercial-scale UVI aquaponic system.
Vegetable
|
Planting Density
(#/m2)
|
Production Cycle Length (weeks)
|
Sales Price
(US$)
|
Annual Income
(US$/m2)
|
Annual System Income (US$)
|
Leaf lettuce
|
20
|
4
|
1.50 each
|
292
|
62,595
|
Romaine lettuce
|
16
|
4
|
1.50 each
|
234
|
50,076
|
Basil
|
16
|
4
|
26.40/kg
|
515
|
110,210
|
Okra
|
3.7
|
12
|
1.10/kg
|
15
|
3,210
|
Cantaloupe
|
0.67
|
13
|
2.99/kg
|
46
|
9,844
|
Chives
|
80.7
|
6
|
1.00/bunch
|
700
|
149,800
|
Conclusion
The UVI aquaponic system represents an appropriate or
intermediate technology that can be applied outdoors under suitable growing
conditions or in an environmentally controlled greenhouse. It is ideal for areas that have limited
resources such as water or level land.
The system is highly productive and intense but operates well within the
limits of risk. It conserves and reuses water, recycles nutrients and requires
very little land. With its small land
requirement it is economically feasible to locate systems close to urban
markets, thereby reducing transportation costs. The system can be used on a
subsistence level or a commercial scale.
The system is simple, reliable and robust. Production is continuous and sustainable as
demonstrated by nearly 10 years of continuous operation in its current
configuration. The UVI aquaponic system does require a relatively high capital
investment, moderate energy inputs and skilled management, though management is
easy if production guidelines are followed.
References
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recirculating fish culture system.
University
of the Virgin Islands, Agricultural Experiment Station, Island
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Rakocy, J.E., J.A. Hargreaves and D.S. Bailey. 1993.
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