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Running head: AQUAPONICS

Aquaponics: The Creation of Liquid Ecosystems for Sustainable Food Production

K.P.B. April 15th, 2013

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Abstract

Aquaponics is a complex agricultural technology that has been in the process of

development over the last few decades. Recently, this modality has come into its own as

a viable method of sustainable food production. With respect to certain kinds of crops

and fish farming, aquaponics production yields can greatly exceed those of aquaculture,

hydroponics and field-grown agriculture by themselves. Most of the available literature

on this topic is from the 1990’s onward and describes both commercial and experimental,

do-it-yourself systems (Diver & Rinehart, 2010). In this literature, a trend can be seen, in

that aquaponics systems require a high level of maintenance and a nuanced understanding

of the complexities of a synthetically created miniature ecosystem. Yet, it also has been

shown that that if a consistent, balanced approach to this sort of agriculture is taken, the

output in terms of sheer production yields of both fish and crops, and the smaller amount

of resource input required to the system make the aquaponics method a favorable

alternative to aquaculture, hydroponics or field-grown agriculture by themselves.

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Aquaponics: The Creation of Liquid Ecosystems for Sustainable Food Production

This is a review of literature on the subject of aquaponics, its development over

the last couple of decades, and some material on the related fields of aquaculture and

hydroponics. It surveys research study reports and proposals conducted by scientists in

universities and government-funded organizations that were published in peer-reviewed

journals or official government reports. It focuses on the nature of aquaponics systems,

their components and the unique challenges in maintaining them. This review also

examines the efficiency of these systems in contrast to other agricultural methods such as

field-grown crops, standalone hydroponics systems and aquaculture fish farming. It

attempts to ascertain whether aquaponics might be a practical alternative to more

traditional agricultural methods.

Background

Aquaponics is a sustainable food production system that integrates recirculation

aquaculture with hydroponics in a symbiotic environment. Hydroponics is a type of

hydroculture that involves the growth of plants in water, without soil. Synthetic mineral

nutrient solutions are artificially added in as fertilizer, which allows nearly all kinds of

plants to grow in water alone. Sometimes an inert medium of perlite, gravel, clay or

another substance is also utilized at the root site of the plants (Diver & Rinehart, 2010).

Plants are able to absorb the essential mineral nutrients they need for growth as inorganic

ions in water.

In aquaculture, certain species of aquatic animals such as fish, snails, crayfish or

prawns are raised in tanks above ground. The fish or other aquatic species are fed some

kind of feed, either synthetic pellets or a more sustainable option, such as naturally grown

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insects or worms grown on restaurant and grocery store food waste (Huffman, 2011).

Waste products or effluents excreted from the fish accumulate in the water over time,

increasing toxicity in their environment. Standalone aquaculture requires frequent

manual removal of these effluents in order for the fish or other aquatic species to thrive.

Instead of removing this waste material manually, bypassing its utility value,

aquaponics systems route this waste water to a hydroponic system where the by-products

from the aquaculture are broken down by nitrogen fixing cultured bacteria, then filtered

out by the plants as vital nutrients, after which the cleansed water is recirculated back to

the fish. This is all accomplished by a system of rearing tanks, troughs, pipes, pumps,

valves, clarifiers, degassing tanks, filters, air diffusers and in some cases, base addition

tanks (Rakocy, Bailey, Shultz & Thoman, 2004),. Environmental factors such as

temperature, pH, total alkalinity, dissolved oxygen and solids, nitrogen and mineral levels

and microorganism infiltration are periodically monitored. Nitrification occurs at a more

base pH level, yet this can be harmful for the fish, plants and bacteria (Tyson, Simonne,

White & Lamb, 2004). This is not always the case, however. Mint plants in particular

thrive on an especially acidic pH (Mustafa, 2010). Sometimes, subtler aspects such as

electrical conductivity, turbidity, chemical oxygen demand, phosphorous levels and

overall water quality are also measured. In commercially scaled systems, calcium and

potassium hydroxide (Rakocy, et al., 2004), as well as chelated iron sometimes are

required as an added supplement (Roosta & Mohsenian, 2012). Floating raft hydroponics

or vegetable beds are used to house the growing plants.

The hydroponics component also achieves an efficiency benefit, in that its

nutrients are supplied naturally from the fish effluent that has been processed and filtered

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by the bacteria and plant roots, instead of being added synthetically at extra financial cost

and effort (Diver & Rinehart, 2010). This cycle of water and nutrient flow is a sort of

synthetic ecosystem, comprised of bacteria, plants and fish living next to or near each

other, depending on the system design. The type of bacteria used also vary the quality of

overall production quite a bit (Tokuyama, Mine, Kamiyama, Yabe, Satoh, Matsumoto,

Takahashi & Itonaga, 2004). Existing hydroponic and aquaculture farming techniques

form the basis for all aquaponics systems. Therefore, the size, complexity, and kinds of

foods grown in an aquaponics system can vary equally as much as any system found in

either distinct farming discipline.

Summary of Literature

Aquaponics

The National Renewable Energy Laboratory, under direction of the EPA and

DOE, recently produced an exhaustive report on sustainable development projects. The

intent of the research contained within revolves around economic redevelopment of the

former Brunswick Air Naval Base. A section of this document contains analysis of

potential greenhouses that utilize aquaculture systems in tandem with thin-film

hydroponics arrays to grow lettuce. The roots of the lettuce plants are submerged

between two layers of plastic that allow for liquid nutrient flow. Nutrients are provided

not from synthetic additive fertilizers as in normal hydroponics systems, but from fish

effluent that is cultured by the same variety of bacteria present in yogurt.

This culturing process improves the usability of the nitrogen present in the fish

waste, and lettuce can be grown in a staggered fashion throughout the year, which

provides full-time employment for workers and yields ~130,000 lbs of lettuce and

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$110,000 in revenue. According to the United States Department of Agriculture, the

average American eats 34.5 lbs of lettuce per year, and 93% of this lettuce is grown in a

portion of land shared between Arizona and California. In shipment across the country to

Brunswick, the fuel cost of this field-grown, non-greenhouse lettuce averages $153,000 a

year, which could be essentially eliminated with local aquaponics lettuce production.

Water use would also decrease by 90% via the use of the hydroponics component. It is

unclear whether this government study was merely theoretical or practically carried out,

however (Huffman, 2011).

Similar large-scale aquaponics systems were empirically investigated by the

University of the Virgin Islands from 2000 to 2004. Red and Nile tilapia were produced

in combination with cultivation of basil and different types of okra. Nile tilapia proved to

be the heartier species of the two fish, yet a substantial annual yield of a few metric tons

of each was obtained. Annual production of basil and okra was dramatically higher than

field production, with aquaponics-produced basil yielding over three times as much as

field-grown basil, as well as providing a high potential for profitability. One variety of

okra grown using the aquaponics system yielded eighty times more than field production;

the other species yielded almost twenty times that of field-grown okra. Batch production

of both kinds of crops yielded the most volume, however nutrient deficiencies became an

issue when production exceeded nutrient generating capacity of the system, making

staggered cultivation the best overall method. A Pythium infection also occurred in the

basil roots at one point. Some issues with snails being accidentally introduced into the

system were managed with red ear sunfish fingerlings to control the snail population. A

pesticide was also used on the crops to control caterpillars. The aquaponics system was

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highly efficient overall, if maintenance intensive, with produce generating $110,210

annually compared to field production at $36,808 per year. With including the fish in

that projection, income would rise to $134,245 per year (Rakocy, et al., 2004). This

system would become a sort of standard for commercial systems and go on to influence

other endeavors (Linky, Janes, & Cavazzoni, 2005).

Small scale do-it-yourself systems are actually quite common with aquaponics

systems. Steve Bird points out that pieces of the system can be assembled from recycled

or common materials. Emphasized in his article is their versatility, that they have been

utilized in places as diverse as Antarctica, the deserts of the Middle East and the jungles

of Thailand, and that this is possible via the different means of protective housing that

one can install (2010). A system based in the Negev desert was even successful utilizing

tilapia in brackish water (Kotzen, 2010). Places like Pakistan may need to rely on this

technology or hydroponics in order to not have a severe population crash in the future

(Sheik, 2006). In an entirely different kind of environment in Thailand, the Asian

Institute of Technology experimented with artificially filtering pond water housing

catfish. They discovered that in growing lettuce, a much higher yield could be had this

way (Sikawa & Yakupitiyage, 2010).

Aquaculture

An aquaculture-only ‘biofloc’ system was also experimented with by Rakocy and

his colleagues. A much larger tank was used than with the aquaponics system they

created, yet fish production levels of Nile tilapia were only about one third to one half

that of the aquaponics system. This is partially due to the more frequent manual removal

and replacement of fish inherent in the aquaponics system structure, making for more

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continuous yields and profit in its case. The reduced yield is also due to the need for

artificial nitrification and denitrification and periodic removal of solid wastes. The

feeding rate and thus the production capacity in aquaculture is limited by the rate at

which microbes can break down ammonia and solid waste. Aeration and water exchange

can speed up production somewhat. This system produced high-density yields for what it

was, and in contrast to the aquaponics system, was easy to manage. Survival rates for the

fish were lower, however this was likely due to the open-air design, which allowed birds

of prey to pester and reduce the fish population. Denitrification tanks and large clarifiers

are extra elements required in aquaculture not necessary in an aquaponics system. Water

exchange is also a built-in feature of aquaponics that is not feasible in all aquaculture

system designs (Rakocy, Bailey, Shultz, Danaher & Thoman, 2002).

One downside of aquaculture is its generation of nitrous oxide, a greenhouse gas.

Interestingly, one of the best ways to minimize this problem is to incorporate aquaculture

with hydroponics, since this recycles nutrients and reduces ammonia and nitrite contents

(Hu, Jae, Chandran, Kim, & Khanal 2012). Ammonia and nitrite create toxicity in

excess, and since aquaponics systems allow for nitrifying bacteria to flourish, they can

convert these other compounds to nitrate (Golz, 1995). At the very least, recirculating

aquaculture systems are superior to regular aquaculture designs in that they save money

on electricity, reduce water usage, and thus give greater return on investment than

traditional systems. The main drawbacks to recirculating aquaculture and aquaponics are

the accumulation of contaminants that cause disease and greater fish mortality. Even

still, such systems have a similarly greater yield than traditional aquaculture (Klinger &

Naylor, 2012).

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Hydroponics

Hydroponics systems are as versatile as they are delicate. The right mix of

mineral nutrient ingredients for the specific plants being cultivated are absolutely crucial.

This kind of agriculture has been around a lot longer than its combination with

aquaculture, and many of these specific mineral prescriptions and other ingredients have

been figured out over the last few decades. In the use of hydroponics in calcerous gravel

present in desert areas, acid and water washes can counteract the effect of lime chlorosis

on cucumber, lettuce, eggplant, tomato and bean plants (Schwarz & Vaadia, 1969). In

lettuce cultivation, the use of tricontanol as a foliar spray nearly doubled leaf weight, and

it tripled growth rate of the plants (Knight & Mitchell, 1987). Australian scientist D.O.

Huett came up with a commercial mineral solution that contained the optimal calcium to

potassium ratio, which he measured with electrical conductivity. The solution increased

calcium content in the plants that he used, as well as increased their leaf weight (1994).

A group of scientists in China discovered that adding selenium to the nutrient solution

enhanced nitrogen and phosphorous absorbtion, as well as reduced sugar content in

lettuce (Qingmao, Lihong & Shijun, 1998). In terms of productivity of hydroponics

measured against aquaponics systems, respectable yields can be had. Elio Jovicich found

with “Spanish” pepper that a range of 3.5 kg· m-2 (1.5 plant/m2) to 7.4 kg· m-2 (3.8

plant/m2) could be produced (2000). According to Dimitrios Savvas, hydroponics has no

adverse effects on quality of fruits and flowers, and the precise control of nutrition allows

for accuracy. An added benefit is that it requires fewer pesticides and other toxic

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agrochemicals than field-grown plants (2003). Aquaponics systems do not have the same

precise level of nutrient control that hydroponic systems possess. Realistically, because

of this, a greater variety of species of plants can be more easily grown with hydroponics

(Cantliffe, D.J., Shaw, N., Jovicich, E., Rodriguez, J.C., Secker, I., Karchi, Z., 2000). An

example of this is the tomato, which is a demanding plant. In one study, no discernable

difference in yield between aquaponics and hydroponics systems was noted (Roosta &

Hamidpour, 2011). Interestingly though, an aquaponics system incorporating tomato

plants was used fairly successfully to reclaim and restore domestic wastewater (Rana,

Bag, Golder, Roy, Pradhan & Jana, 2011).

Conclusion

Aquaponics systems present a unique, resourceful way of generating both produce

and protein. The high-density yield that is possible with commercial scale aquaponics is

promising, and once implemented, it could lead to the solving of food shortages in areas

of the world that are less privileged or more strained for resources. Even small scale

systems proliferated in abundance could make a profound impact on the means through

which people obtain their food. In comparison to aquaculture or hydroponics systems by

themselves, aquaponics has some clear advantages over both, if managed with care and

diligence. The replication of natural processes with additional artificial measures in both

aquaculture and hydroponics put them at a disadvantage in certain respects over

aquaponics designs. That being said, to obtain an efficient and predictable yield of both

fish and produce from aquaponics requires a nuanced and experienced touch. Getting the

balance right with the nutritional input for plants from effluents and management of

nitrifying bacteria appears to be especially challenging.

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Since the aquaponics modality attempts to replicate a miniature form of

ecosystem, it is naturally more complex than aquaculture or hydroponics alone. These

two respective systems are slightly easier to manage, because in one case, waste is being

dealt with somewhat artificially and manually; in the other, the nutritional component is

entirely synthetic. Also, upon reviewing the available literature, it is challenging to

discern concrete one-to-one comparisons of produce and fish yields in terms of kilograms

per meter or metric tons; very little of the material surveyed yielded obvious conclusions

about such things. Anyone can experiment with a small aquaponics system and learn by

trial and error, but a great deal of education, forethought and repeated empirical

experience seem to be key in being successful in the long run with this kind of

agriculture. Aquaponics has not been implemented on a wide scale; only time will tell

whether it can become a pragmatic replacement for a portion of agricultural production.

Questions for Further Research

Of interest is the efficiency of aquaponics systems as an agricultural technology

for consistent generation of produce and protein in the long-term, potentially replacing at

least a part of the highly industrialized, tightly controlled food industry. The literature

has shown that these systems have potential as a sufficiently sustainable and abundant

method for partial supplementation of food production, if managed correctly. Since

aquaculture requires extra time and equipment in some cases and hydroponics requires a

lot of nutritional input at extra cost, perhaps aquaponics would be a better solution for

some, especially if some sort of widespread educational agenda was put forth. Might this

technology be worthwhile of implementation within local communities, in order to make

them more stable and self-reliant, less dependent on the centralized food industry? Could

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low-income communities especially benefit from relatively small-footprint aquaponics

systems as a way to decrease problems of nutritional deficiency from poverty?

Mercury content in fish is also a health risk that many consumers consider in their

consumption levels of fish. It seems that aquaponics could be a pragmatic way to work

around that problem. Also, as ocean acidification increases, making fish populations

more vulnerable to endangerment or extinction, could aquaponics systems ‘bring certain

species out of the ocean and onto land’ so to speak, preserving them in a sense? These

are important questions for the future, yet the most fundamental aspect of whether or not

aquaponics stands against conventional field agriculture and different types of

aquaculture and hydroponics in terms of raw efficiency has not been entirely answered.

Obviously, several aspects of each kind of cultivation are unique to their method and

therefore cannot be objectively compared. Yet, a multifactorial research study design

that independently compared all of these systems against each other, utilizing identical

components in size and makeup amongst their respective corresponding elements might

be warranted. That way, variables would be reduced, and the data obtained could be

interpreted within a smaller paradigm of confounds. Perhaps this kind of study should be

conducted on both small and commercial scales as well.

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