Aquaponics—a study into the effectiveness of the symbiotic relationship between aqua-farming and hydroponics under different climates and market conditions, supplemented by solar energy
Author: Darynne Lee
Peer Reviewer: Lauren Cho
Professional Reviewer: James Truncer
("1987: Brundtland," n.d.).
“Sustainability is the ability to meet the needs of the present without compromising the ability of the future generations to meet their own needs”
Over the years, conventional agri-farming and aqua-farming have led to many unsustainable practices. Conventional agri-farming has depleted about one-third of the soil globally (Arsenault, n.d.) and used up 38.6% of land and 70% of freshwater (Barbosa et al., 2015). Aqua-farming has been growing at a rate faster than population growth: an FAO report shows that, from 2004 to 2009, aqua-farming grew by 31.5% whereas world population only grew by 6.3% (2014 World, n.d.). This disproportionate increase in aqua-farming versus population growth has resulted in the destruction of ecosystems along coastlines, eutrophication of effluent water, and the introduction of artificial medication into food cycles.
Nevertheless, the demands on agri-farming and aqua-farming for food and employment are only growing with an increasing population. Over 3 billion people worldwide depend on seafood for 15% to 20% of their daily protein and over 1 billion people are employed in agriculture worldwide, in some cases, engaging more than 60% of the working population, especially in developing countries (2014 World, n.d.). Given our dependence on agri-farming and aqua-farming to feed the growing population, we have to devise new methods of farming that are more sustainable; otherwise, the harmful impacts on the environment will only exacerbate.
One solution to these challenges is aquaponics, a closed-loop system that combines aqua-farming and hydroponics in a symbiotic relationship that is carried out in greenhouses with fish tanks or ponds. Fish feed is digested by fish, and effluent water containing fish waste is pumped into grow beds with hydroponic plants. The root bacteria in these hydroponic plants break down the fish waste into nitrate, which is absorbed as plant food. In fact, the plants act as “biofilters,” cleaning the water, which is then pumped back into the fish tanks.
An aquaponic system is eco-friendly since crops are grown under controlled conditions and do not require soil or large land areas. This means that the harmful effects of soil depletion are reduced to zero. Furthermore, all water is reused and recycled, thereby reducing waste through surface water runoff and pollution of freshwater to zero. The root bacteria of hydroponic plants convert all fish waste containing toxic ammonia into nitrate, which is absorbed as plant food, replacing any need for artificial fertilizers. The greenhouse conditions and lack of soil substrate also reduce plant-eating insects and disease-causing pathogens (which like to live in soil), rendering pesticides redundant.
Overall, aquaponics is very effective in reducing environmental impacts while producing higher yields compared to conventional agri-farming and aqua-farming alone. However, the biggest downside is the amount of energy required to maintain greenhouse conditions and production all year round. Heating, lighting, water pumping and monitoring conditions with computerized systems all require energy. The amount of energy needed depends heavily on the climate and geographical location of the farms. After analyzing the design elements and commercial viability of aquaponic systems in detail, this paper argues that combining conventional agri-farming and aqua-farming in the practice of aquaponics, coupled with solar energy, is a viable solution for sustainable farming.
Section 1: How much do aquaponic systems reduce the environmental impact from agri-farming or aqua-farming alone?
The disadvantages of conventional agri-farming include “high and inefficient use of water, large land requirements, high concentrations of nutrients and pesticides in runoff of surface water, and soil degradation” (Barbosa et al., 2015). In particular, artificial fertilizers are harmful because they cannot completely replenish all the minerals and nutrients taken up by the crops. This leads to over-farming of the land and soil depletion while the runoff of excess chemicals pollute freshwater sources around the farms. Although pesticides can increase agricultural productivity, they are poisonous to human beings and animals when handled improperly.
The disadvantages of aqua-farming alone include the destruction of natural ecosystems along the coastline, salinization and acidification of the soil, eutrophication and nitrification of effluent water, and the introduction of artificial medication into food chains. For example, preliminary calculations reveal that the waste produced by the intensive farming of three tons of freshwater fish is equivalent to the untreated waste produced by 240 land inhabitants (Avnimelech, 2015). Non-consumed fish feed (especially due to overfeeding measured by Feed Conversion Ratio (FCR), the mass of input divided by mass of output), lixiviation (the process of separating soluble from insoluble substances), and the decomposition of dead organisms, are the main causes of eutrophication of the water column. Only 20% to 50% of the total nitrogen supplemented to fish is retained as biomass, whereas the rest becomes sediment in the water column and is eventually discharged as effluent water into rivers (Martinez-Porchas & Martinez-Cordova, 2012). Eutrophication causes diverse impacts such as phytoplankton blooms and red-tide (Alonso-Rodriguez & Paez-Osuna, 2003).
To understand the advantages of aquaponics, we can refer to a study done in 2012 by University of Arizona Cooperative Extension on the hydroponic growing of lettuce. Lettuce is the second largest vegetable crop by weight grown in the United States. Arizona accounted for 29% of total U.S. lettuce production, and the state used up 69% of all freshwater withdrawal solely for agriculture (Barbosa et al., 2015). Thus, finding a sustainable alternative to conventional farming in Arizona is crucial. The study demonstrated that hydroponics offered much higher yields for lettuce compared to conventional farming. Greenhouse conditions allow plants to grow faster, shortening harvest times regardless of weather and increasing lettuce yields: yields from hydroponics were 11 times higher and used 12 times less water than conventional farming (Barbosa et al., 2015). However, the energy required for hydroponics was 80 times more than conventional farming because the climate in Arizona varied from 14°C in winter to 35°C in summer, which meant that heating and cooling systems were required to maintain greenhouse temperatures at a constant of 24°C (Barbosa et al., 2015). In water-scarce Arizona, aquaponics can be a huge water-saving alternative to conventional farming, but energy demands must be met using renewable sources, as discussed later in the paper.
If hydroponics is combined with a recirculating aquaculture system (RAS), all the wastewater is recycled, and less than 10% of the total water needs to be replenished each day for the loss due to evapotranspiration. Eutrophication and nitrification of effluent water is greatly reduced as the removal efficiencies are 85% to 98% for floating solids and organic matter, and 65% to 96% for phosphorus (Grozea & Blidariu, 2011). This means that the FCR for aquaponics can be reduced to between 1.25 and 0.9, depending on the factors chosen for the system (Wilson, 2004). Due to the greenhouse conditions, all natural methods can be used for growing both vegetables and fish. Artificial pesticides cannot be used for vegetables as they percolate quickly into the water and are toxic to fish and root bacteria, so physical barriers are used to keep insects out. Microscopic parasites such as cyclospora and cryptosporidium are biologically controlled by increasing the polyculture of fish, since diversity increases their resilience to disease (Barbosa et al., 2015). Furthermore, since vegetable crops are grown in a soilless culture, soil diseases are non-existent, and the destruction of coastal ecosystems and salinization/acidification of soil are no longer a concern. Additionally, artificial growth hormones are not used in aquaponics because fish growth rates recorded through numerous experiments are healthy and can be increased through natural methods. For example, switching to a rack (vertical) and raft (horizontal) system for growing vegetables not only increases vegetable crop yield, but also generates an increase in fish yields (Salam, Asadujjaman, & Rahman, 2013).
Therefore, combining RAS with hydroponics not only respects the principles of sustainable agriculture, but also gives the possibility of increased economic efficiency with higher crop yields. Hydroponics alone requires expensive nutrients for plants and periodic flushing of systems, leading to waste disposal issues, whereas the nutrient rich water of aqua-farming alone needs to be replenished with freshwater everyday. By combining both systems in a symbiotic relationship, the effluent water from aqua-farming is utilised as a food source for vegetables in hydroponics, which in turn acts as a biofilter, cleaning the influent water required for aqua-farming. This arrangement turns the negative aspects of both systems into strong positives.
Section 2: Typical design of a modern aquaponic system
There are many factors that go into designing a successful aquaponic system. See Fig 1. The major ones are the type of fish, the composition and amount of fish feed, the type of vegetables grown, the medium for growing vegetables, the nitrification process, and the monitoring of water quality.
For the RAS portion of aquaponics, all proper fish husbandry practices apply, and the water quality and growth in fish stock have to be monitored periodically. Fish can be grown with a low stocking density (10kg per 1000L) or high stocking density (100kg per 1000L), depending on the type of fish and availability of water (Wilson, 2004; Purdue University, 2011). Types of edible fish suitable for aquaponics include tilapia, silver perch, jade perch, murray cod, barramundi and trout. Pangasius and tilapia are more prevalent in aquaponics as they have the ability to tolerate wide environmental parameters, are versatile in terms of fish feed, and have a fast growth rate. Fish feed varies by species of fish, but it needs to be of a floating variety. Whether by auto or demand feeding, intake needs to be regulated according to the growth cycle of the fish. Generally, more feed is needed at the beginning of the growth cycle and less later on. Each growth cycle is 90 to 110 days, with at least 3 cycles per year. If the amount of fish feed is not properly regulated, the FCR will rise, and the unconsumed fish feed accumulated at the bottom of fish tanks must be removed. Fish waste and unconsumed fish feed is pumped from the fish tank into a swirl filter (also called a settler), which is an upside-down cone shaped tank where lixiviation takes place. Water is dripped into the swirl filter so that it swirls around in one direction slowly, allowing heavier solids and sludge to sink as sediment and drain through a tap at the bottom of the tank. Sedimentation is also where anaerobic mineralization of waste occurs which, over time, breaks down waste and releases nutrients back into the influent water for the plants (Wilson, 2004). A percolate filter may be added to filter out any remaining solids from the water after it passes through the swirl filter. However, this filter is not strictly necessary if the swirl filter is designed correctly and overfeeding is minimised.
As the nutrient-filled water flows under the hydroponic grow bed, the process of nitrification takes place to cleanse the water. Natural bacteria from the roots of crops convert ammonia present in the water to nitrite and then into nitrate. An organic biofilter can be added before this stage to jump-start the process of nitrification, but it is not strictly necessary if the system is designed well. An organic biofilter uses beneficial microbes, bacteria and enzymes to break down ammonia before root bacteria accumulates sufficiently when the plants are still young (Aquaponics Training Academy, 2016). The nitrification process converts toxic fish waste into plant food.
Plant grow beds are a soilless environment involving a growing medium such as gravel, perlite, ceramic or stone, or floating rafts and vertical racks. The type of growing medium for an aquaponic system depends on the type of vegetables. At the preliminary stage of deep-water raft aquaponics, seedlings are first placed in net pots or flat seed tables with a planting medium such as coconut husk. After the seeds germinate into baby plants, they can be placed into either rafts or racks, which further maximize the space for higher crop yield. Types of vegetables include soybeans, lettuce, basil, parsley, red russian kale, okra and water spinach (Aquaponics Training Academy, 2016). Leafy greens like lettuce and herbs perform better in newly set up farms, whereas fruit-bearing plants like tomato and cucumber perform better in mature systems (Salam, Asadujjaman, & Rahman, 2013).
Aquaponics takes place in greenhouses, where all factors are controlled. Some elements of infrastructure include energy for cooling or heating, water and room temperature, and lighting. The amount of sunlight can be supplemented with artificial lights like high output fluorescents, light-emitting diode LED, red light, blue light, and metal halide light. Each type of light has different characteristics. For instance, red light is best for seedlings and budding plants, whereas metal halide light is best for large plants in cold climates because it is very intense, high in the blue spectrum, and produces heat. Below is an evaluation of the impact of various design aspects on the effectiveness of aquaponic systems.
The Relationship of FCR to Fish Feed
FCR of the fish is extremely important because it is a measure of the food intake required to create a specific amount of fish biomass. An FCR of 1.0 is more efficient than an FCR of 2.0 because it takes half as much food to achieve the same weight gain. A low FCR such as 1.0 would mean more of the nutrient in fish feed goes into building body mass and less goes into waste. Hence, a fish with lower FCR produces less nitrate nutrient waste than one with a higher FCR (Wilson, 2004). The amount of fish feed must be varied during the life cycle of the fish to reach an FCR of 1.0 but not less than 1.0. Otherwise, there will be no nutrients left for the plants.
The Impact of Fish Feed on Fish and Vegetable Yield
The protein content of fish feed has an impact on fish and vegetable yield. For example, murray cod requires 43% protein in its feed, whereas tilapia requires 37%. Studies indicate that a 50% protein content is ideal for improving vegetable yield, making murray cod a better choice than tilapia. This is because the amount of nitrate increases with the protein content of fish feed. Hence, the higher the percentage of protein in the fish’s diet, the more plant food available, optimizing the plant yield (Wilson, 2004).
Types of Vegetables and Fish
Selecting the types of vegetables and fish that best fit an aquaponic system depends on the climatic conditions of the farm—whether it is a native species and the availability of fish feed. For instance, farming barramundi would require high heating costs in cold climates as barramundi works best in warm temperatures. Another example is murray cod, which is new to tank culture and requires more space to grow. If the size of the farm is limited, murray cod would not be the best fish to farm (Desima, 2016). The combination of fish and vegetables is important for diversity, which will maximize the resilience of the system. If only one or two types of fish or vegetables are used, the system becomes overly specialized and vulnerable to shock events like diseases.
The Impact of Type of Vegetables on Fish Yield
A study in Bangladesh showed that different types of vegetables can affect fish yield. Fish production was significantly higher (>10kg/tank/cycle) when paired with water spinach as opposed to taro and tomato (about 7kg/tank/cycle). A reason for this outcome is the removal of ammonia from the influent water to fish tanks. Compared to taro and tomato, spinach has a faster rate in converting ammonia to nitrate. Achieving zero ammonia in the influent water for fish is crucial to the survival of the fish (Salam, Hashem, Asadujjaman, & Li, 2014).
The Impact of Quality and pH of Water
The level of nitrogenous compounds (ammonia, ammonium, nitrite and nitrate), phosphate, and dissolved oxygen should be monitored periodically to ensure optimal conditions for the growth of vegetables and fish (Salam, Asadujjaman, & Rahman, 2013). Plants require minerals like calcium and potassium to grow properly, and the recommended Ca:K (calcium to potassium) ratio for maximum plant production is between 2:1 and 6:1, depending on the vegetables grown (Savidov, Hutchings, & Rakocy, 2005). The pH value of water needs to be at a range of 7.0 to 8.5 (Salam, Asadujjaman, & Rahman, 2013). Mineral supplements can be added to lower the pH value of water, and oyster shells can be used as a natural alternative to artificial calcium buffers as they are a source of soluble calcium (Aquaponics Training Academy, 2016).
The Impact of Growing Medium on Fish Yield
The type of growing medium depends on both the type of vegetable chosen and its impact on fish yield. Nutrient Film Technique (NFT) is a traditional growing method used in hydroponics, whereas gravel, raft and rack are newly invented ones. Studies that investigated different growing mediums showed that NFT was 20% less efficient than gravel beds and floating rafts in terms of plant yield and nutrient removal. This is because plant roots in the gravel bed and raft system are 100% in contact with the water column. In comparison, the plant roots in NFT only have up to 50% contact with water, slowing down the process of plant growth and nitrification (Wilson, 2004). Overall, floating rafts create the most optimal combination of fish yield and plant yield. See Table 1.
Hence, the success of an aquaponic system depends on several factors. Each factor has its own set of parameters but combining them means that the factors must operate in tandem within the entire ecosystem as they are codependent. Aquaponics is an example of biomimicry in a controlled environment where physical, chemical and bacteriological environments are replicated. Ideally, sensors monitoring the different factors would be connected to computer programs that maximize the yield while correcting for potential systemic failures.
Section 3: Waste Production and Removal
The process of nitrification is central to bioproductivity in both natural and artificial ecosystems. Ammonia, which is toxic to fish, is a main component of fish excrement that is released when fish waste is broken down. The process of nitrification takes place in the roots of plants and involves nitrifying bacteria oxidizing ammonia in a two-step process (Savidov, Hutchings, & Rakocy, 2005). The process reduces the level of ammonia in the water and converts fish waste into nitrite and then into nitrate for plant food, connecting the output from fish farming with the input required in agri-farming (Purdue University, 2011). Therefore, the nitrogen cycle not only eliminates the toxicity of the influent water to fish tanks, but also recycles organic fish waste into plant food. This increases the growth rate of vegetable crops and removes the need for artificial fertilizers. Trace minerals like potassium, calcium and iron may need to be added to supplement fish feed as these are absorbed by plants and removed from the system when plants are harvested for sale. See Fig 2.
During the two-step oxidation reactions, energy is released. Nitrifying bacteria are chemoautotrophs, which are organisms that obtain energy from the oxidation of electron donors. The energy released is used to synthesize organic compounds for plant food (like nitrate) from inorganic compounds (like ammonia). Chemosynthesis is similar to photosynthesis, in which photoautotrophs like chlorophyll in plants synthesize organic compounds (like glucose) from inorganic compounds (like carbon dioxide, water and sunlight). Photosynthesis provides plants with carbohydrates required for energy, whereas nitrification provides plants with organic compounds required to form protein and chlorophyll ("Why a Plant," n.d.).
The two-step process takes place with nitrifying bacteria acting as catalysts. The first step is the breakdown of ionized ammonia (NH4+) into nitrite (NO2-), catalysed by Nitrosomonas bacteria present in the roots of plants.
2NH4+ + 3O2
-> 2NO2- + 4H+ + 2H2O
The second step is the conversion of nitrite (NO2-) into nitrate (NO3-), which is catalysed by Nitrobacter bacteria.
2NO2- + O2
The relative levels of ammonia, nitrite and nitrate produced by nitrification fluctuate over time in an aquaponic system. See Fig 3.
To achieve the optimum state of bacteria growth for chemosynthesis and nitrification, the temperature, water pH, chlorine and dissolved oxygen (DO) levels must be controlled. Nitrifying bacteria die at under 0°C and over 49°C, and the preferred temperature range is 25°C to 30°C (Baliga, n.d.). The water pH range can fluctuate from 6.5 to 8.5, but the optimal range is 7.1 to 7.8 for Nitrosomonas bacteria and 7.6 to 8.0 for Nitrobacter bacteria (American Water Works Association, 2002).
The chlorine level in aquaponics must be zero because chlorine kills nitrifying bacteria and fish. Urban tap water is often sterilized with chlorine, so tap water must be left in an open container for more than 48 hours to allow the chlorine to evaporate completely (Baliga, n.d.). There also needs to be sufficient DO levels, as four oxygen gas molecules are needed to break down two ammonia cations into two nitrate anions. A rack and raft system is superior to raft alone in terms of DO because water flowing down through the racks absorbs more oxygen from the atmosphere. Furthermore, the type of vegetable affects the effectiveness of the nitrogen cycle as different root systems encourage different levels of bacterial growth. The rate and impact of ammonia removal was tested on water spinach, taro and tomato in Bangladesh. Although all three plants removed nitrogenous-compounds from water, the water spinach had the fastest rate of removal, as the root system was more conductive to Nitrobacter growth. This produced better conditions for fish, leading to a higher weight gain and a survival rate exceeding 90% (Salam, Hashem, Asadujjaman, & Li, 2014). Results clearly demonstrate the importance of nitrification to the symbiotic relationships in aquaponics: healthy nitrifying bacteria growth leads to greater nutrient removal, resulting in higher vegetable yields. This in return leads to cleaner water, which raises the biomass gain and survival rates for fish, resulting in higher fish yields.
Nitrification and Disease Prevention
Healthy bacteria growth is also important to disease prevention and improving resilience to crop failure. Results from studies in hydroponic systems show that the systems can be made less susceptible to infections through increasing different types of bacteria in the nitrogen cycle and adjusting the temperature of the water. Common plant diseases in aquaponics include Phytophthora, Pythium and Fusarium. Since horticulture cannot be performed in a sterile environment on a commercial scale, insights into the population dynamics of pathogens and plants’ resilience under natural conditions is essential. A study from the Netherlands used next generation sequencing (NGS) to identify different types of bacteria and their impact on population dynamics by measuring the weight of chrysanthemum grown in deep flow systems (Beerens, Blok, Eveleens, Vermeulen, & Streminska, 2017).
It was observed that water left in the open will naturally be colonized by highly diverse bacterial populations, some of which are harmful to plants. On the other hand, inoculation of the water from a deep flow pond results in uniform populations of healthy bacteria in the long run, which ultimately increases the resilience of plants to disease. Since NGS is now faster and cheaper, ongoing research in this field has made it easier to isolate and identify new species of bacteria and understand their functions within the nitrogen cycle.
In conclusion, the healthy growth of nitrifying bacteria is extremely important in aquaponics. Much is already understood regarding the role bacteria play in converting ammonia to plant food, but more research is needed to understand how they prevent disease and improve resilience to crop failure (Beerens, Blok, Eveleens, Vermeulen, & Streminska, 2017).
Section 4: Aquaponics and Solar Energy
In aquaponics, the biggest impact on the environment is the energy consumption for maintaining greenhouse conditions and pumping water.
Energy requirements for aquaponics are extremely similar to those for hydroponics, so we can refer to the Arizona study to draw some parallels. Figure 4 part (a) shows the energy use per kg of lettuce using hydroponics versus conventional means. Part (b) is a pie chart breaking down the energy use of hydroponics. Part (b) shows that hydroponic energy requirements consist of heating and cooling (74,000kJ, 82%), lighting (16,000kJ, 17%) and pumping water (640kJ, 0.7%). Part (c) is the breakdown of the energy use of conventional agri-farming (Barbosa et al., 2015).
If solar energy is adopted, one single solar panel can generate 300 to 350 watts per hour. In desert regions such as Arizona, average direct sunshine is 8 hours (Aggarwal, 2019), generating 2.4 to 2.8 kWh of solar energy per panel per day (approx. 1,000 kWh/y). The energy use in growing lettuce was 90,000kJ/kg/y (25.2 kWh/y, where 1kJ = 2.8*10-4 kWh), which means that 1 solar panel can support 40kg/year of lettuce yield. In Arizona, the average lettuce yield was 40kg/m2/year, so each solar panel (measuring about 1.5m2 in the area) is sufficient to support one square meter of lettuce production.
In arid regions such as Northern Mexico, average temperatures range from 20 to 30°C, so heating and cooling are not required and electricity is only needed for lighting and pumping water (16,000kJ/kg/y plus 640kJ/kg/y = 16,640kJ/kg/y (4.68 kWh)). In addition, the average sunlight hours are 11 hours per day, so 3.3-3.9 kWh (approx. 1,400 kWh/y) of solar energy can be generated per panel per day. Compounding more energy produced from sunlight with less energy consumed by aquaponics implies that 1 solar panel can support over 300 kg/y of lettuce.
The cost of solar panels (USD100 per panel) and batteries (USD25 per battery) for storing power at night should be factored in, but solar panels and batteries have a useful life of 25 years and 10 years respectively. Amortising the cost results in an extra expense of USD6 per year on average. Supported by income generated from selling 300kg of lettuce, the cost efficiencies should be obvious after deducting all other production costs, which vary from farm to farm.
Solar energy in different climatic conditions
We now turn to the feasibility and commercial viability of aquaponic systems in different locations. To achieve maximum profit for farmers, the types of vegetables and fish have to be adapted for local market conditions and running costs must be kept low. Below is an examination of the feasibility of solar-powered aquaponics in two different scenarios: temperate climate and tropical climate.
In Canada, temperatures are cold and sunlight is scarce, but consumers are willing to pay more for organic foods. Tilapia growth trials were carried out at the Brooks aquaponics facility in Alberta, Canada, to test out the feasibility and commercial viability of different types of vegetables with various conductivity factor (CF) levels. CF levels measure the vegetables’ ability to extract nitrogen and their tolerance to different mineral concentrations. The group with medium CF (10 to 20) performed the best: lettuce, basil, chives, water spinach, swiss chard and parsley, as they were grown at an air temperature of 22 to 25°C with a 16 to 8 hour day-to-night ratio. On the other hand, cucumber and tomato, traditionally grown in hot sunny climates, did not grow well, as temperatures were still too cold and sunlight was insufficient, resulting in root rot. Overall, 60 different crops were tested in this temperate climate, with swiss chard and water spinach producing the highest yield and high value herbs like basil the most profitable. However, energy costs were not factored into the study. Canada receives only 4 to 6 hours of sunshine per day on average and even less in the winter, when the most energy is required for heating. Unless another source of renewable energy can be found, solar powered aquaponic systems will struggle to be commercially viable in temperate regions like Canada (Savidov, Hutchings, & Rakocy, 2005).
Bangladesh has a tropical climate, with plenty of sunshine (on average 10 hours a day) and hot temperatures (25 to 33°C all year). However, unlike customers in Canada, consumers in this developing country are too poor to pay a premium price for organic vegetables, so more emphasis should be put on improving fish yields. A study was made involving three separate experiments on taro, tomato and water spinach grown with pudina fish and tilapia fish. Since lighting, heating and cooling are not required, total energy requirements are 1% of those in temperate regions and can be easily met with solar energy. Economic analysis of an experimental aquaponic system indicates that farming pudina fish and water spinach under a raft and rack system produces the highest benefit to cost ratio and is the most profitable. Fish and vegetable yields are three times greater due to higher planting densities, and the revenue from pudina fish is thirteen times more than the revenue from vegetables (Salam, Asadujjaman, & Rahman, 2013). Meeting the energy requirements with solar power would only add marginal costs similar to those for arid regions like Northern Mexico and would thus be commercially viable.
A working aquaponics system powered completely by solar energy has been built in Togo, West Africa. ABWE International, Christians for Worldwide Evangelism, and Morningstar Fishermen partnered to construct a solar-powered aquaponics facility in the village of Bodje. Bodje has no running water or electricity and has a population of approximately 1,000. The Togolese received education on the factors and techniques of aquaponics, and can now feed their own population independently. The system became financially profitable during its first year of operation and proves that aquaponics coupled with solar energy can be commercially viable even where there are challenges such as water shortage and low income ("Agricultural," n.d.; ECHO Community, n.d.).
Combining aquaponics with clean solar power would solve food security issues, conserve water, reduce carbon emissions, and produce extra income for farmers. Solar powered aquaponics has a greater energy return on investment than conventional agri-farming and aqua-farming alone and greatly reduces the harm on the environment.
Overall, aquaponics is a very effective biomimicry that combines the benefits of hydroponics and aquaculture, creating a symbiotic environment for fish and vegetable crops. It is a closed-loop system in which fish feed is digested into fish waste, fish waste is broken down through nitrification into plant nutrients, and plants and fish are sold for commercial profits. Aquaponic systems attempt to minimize their environmental impacts to zero as they are carried out in controlled greenhouse environments. Wastewater discharge is reduced to zero. The use of chemical fertilizers, insecticides and pesticides, and growth hormones are reduced to zero. The only shortcoming is that the energy required to maintain greenhouse conditions is higher than in conventional agri-farming. The amount of energy required is highly dependent on the climatic conditions of the location; tropical climates and arid regions require much less energy than temperate climates. However, renewable energy sources such as solar power can be combined with aquaponic systems to further improve the environmental benefits and reduce the overall costs to farmers and consumers.